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Statistical Accuracy of Internet Weather Forecasts

CowboyNeal posted more than 7 years ago | from the betting-men dept.

Math 189

markmcb writes "Brandon Hansen considers the statistical accuracy of popular on-line weather forecast sources and shows who's on target, and on who you probably shouldn't rely. Motivated by a trip to a water park that was spoiled with hail despite a 'clear sky' forecast, he does a nice job of depicting deviations, averages, and overall accuracy in a manner that stats junkies are sure to love."

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The more the merrier? (4, Interesting)

Reverse Gear (891207) | more than 7 years ago | (#17946446)

What a nice piece of work.

I can't help but smile a bit that MSN weather in this test turns out to be the absolutely worst when it comes to accuracy in almost all categories.

I would think there is a lot of difference on how the forecasts are made in the different channels, some of them probably do get a lot of their information from meteorologist working on their own stations. I wouldn't wonder if MSN doesn't have a meteorologist (or maybe only one) working to provide their forecasts.
Computers and simulations play a big role in predicting the weather today, but human eyes are worth a lot still.

I don't myself live in the USA, so my primary use of these are to check on when there is severe weather in areas where I know someone.
I have gotten used to check on weather underground for this information, I haven't checked on many other weather channel, but I feel quite well capable of following what is going on in the USA with tornadoes and such here from Denmark.

For a long time we only had one weather forecast service here in Denmark, a national institute. Since a primarily private TV station (TV2) a few years ago started their own weather forecast service, I really feel the national institute have been pulling themselves together and have provided many services that they didn't provide until now. So even though some of the services provides terrible accuracy they might still serve a good purpose in giving the other services competition and thereby forcing them to improve also.

When I am really dependent on the forecast I tend to study the information behind the simple prediction of the given weather, that way I am also much better prepared for possible scenarios, knowing which front move where and can better "read the skies".

Re:The more the merrier? (4, Interesting)

Gabrill (556503) | more than 7 years ago | (#17946518)

It seams odd to me that he started the project because of rain, and then completely ignored rain in his observations. Otherwise, the study was very cool.

Re:The more the merrier? (-1, Troll)

Anonymous Coward | more than 7 years ago | (#17947158)

But many open source projects can't even predict a release date accurately. Take the X.org project. X11R7.2 was scheduled for release on December 11, 2006 [x.org] . Of course, it's now nearly half-way through February of 2007, and we have yet to see this release. Does anyone know when this will actually be released?

Keep in mind that the open source developers basically have some control over when they release their software. Contrast this to the weather, which in many instances is quite unpredictable, even with years of data to work with.

Re:The more the merrier? (1)

Reliant-1864 (530256) | more than 7 years ago | (#17947388)

you're looking at a prediction that was made months in advance. How accurate are weather forecasts at predicting the weather on a specific day 6 months in the future?

Re:The more the merrier? (1)

Krakhan (784021) | more than 7 years ago | (#17947508)

And how is this different amongst proprietary software vendors, such as Microsoft? *Cough* Vista *Cough*

Re:The more the merrier? (1)

chrismcdirty (677039) | more than 7 years ago | (#17947446)

The absolute most reliable place to go for weather prediction (and emergency information) in the US is the Nation Weather Service. [noaa.gov]

Re:The more the merrier? (3, Informative)

Hoi Polloi (522990) | more than 7 years ago | (#17948434)

That's where I go for my weather online. Let's face it, all of the other weather services depend on NOAA for their base data anyway so you might as well go to the source. I do find that the NOAA predictions tend to err on the conservative side though (always predicting a chance of precipitation on dry weeks, etc).

NOAA/NWS (4, Interesting)

zoward (188110) | more than 7 years ago | (#17946476)

I use the NWS website, mostly because I hate all the annoying flash ads on most of the other sites. I was also under the impression that most of these sites get their information from the NWS and pass it along to you (along with a bucket of ads). There was a lot of complaining amongst the popular weather sites when the NWS opened its own web site.

Re:NOAA/NWS (1)

senatorpjt (709879) | more than 7 years ago | (#17946636)

Yeah, I was surprised. Apparently, all the sites are different.

Re:NOAA/NWS (3, Informative)

limecat4eva (1055464) | more than 7 years ago | (#17946666)

I'll second that. Personally, I love the 48 hour graphs [noaa.gov] for being clean, simple, and easy to understand. And quick to load.

Re:NOAA/NWS (2, Interesting)

smokin_juan (469699) | more than 7 years ago | (#17947312)

Absolutely! Even if the graph is "wrong" you still get an approximate idea of what's supposed to happen. Hope you like the daylight indicating shading... it was my idea ;). Too bad they didn't implement the suggestion to change "48 hour period" to a drop menu that'd let you show 48, 72, 96 hours or the whole 5 days.

Anyway, I'm surprised this is the first time I've seen (would've seen if the site weren't 'dotted) forecast accuracy data. With everyone claiming their weather is the most accurate, you'd think someone would've tried to prove it before now.

Re:NOAA/NWS (3, Informative)

istartedi (132515) | more than 7 years ago | (#17946756)

Amen to that. NWS is one example where a government funded program actuallly WORKS. Clean, simple, Flash-free. It's been reliable enough for me. I was able to successfully plan for an outside project almost a week in advance with their long-range forecasts. You have to learn how to use these things a bit, based on your area. For example, here in DC during Summer, it may or may not rain in the afternoon, and nobody can predict if it will actually rain on a particular spot. That's because most of the rain comes from brief thunderstorms that pop up. In winter, they can tell you if a snowstorm will be nearby, but not if it will actually snow or how much. OTOH, sunny vs. rainy and general temperature predictions work pretty well. As an experienced user, I've learned to recognize which types of weather systems are predictable, and which aren't (e.g., Alberta Clipper -- easily predictable temperature drop vs. Gulf low snowstorm--extremely difficult to get the snow total in advance). Other areas have their own peculiarities too I'm sure.

Senator wanted to halt NWS website. (2, Informative)

Radon360 (951529) | more than 7 years ago | (#17947660)

FWIW, former senator Rick Santorum (R-Pa) was gunning to prohibit the NWS from providing forecast information directly to the public. Why? AccuWeather, a Pennsylvania-based company was lobbying him to do so on the basis that the government should not be undermining private corporations business interest. In other words, Accuweather wanted to continue to sell their forecast products without the free competition from the NWS forecast products.

As someone who relies upon information from the NWS, I'm glad it went nowhere, and also glad to see that he didn't get re-elected so he doesn't have the chance to reintroduce such a stupid idea.

Re:NOAA/NWS (3, Interesting)

knightri (841297) | more than 7 years ago | (#17947684)

In the US today, two major organizations release weather forecasts, the National Weather Service and AccuWeather which is based in central PA. However, both of these services get their information from the same source, the satellites, and base their forecasts on the runs of the various computer models. The major computers are the GFS, the NAM, the UKMET and the ECMWF. There are many more though and each is fed the satellite data/ground observations etc to help make a forecast. Some computers, like the NAM only go out 96 hours, while others like the GFS go out 15 days. I live in NJ, and currently, most of the major computers have a serious snow storm headed our way for next week. One area where I find the computers lacking is that they don't know how to respond to new snow falling on the ground. For example if a major snowstorm were to cover a large portion of the country with snow, the temperature in those areas would be 15 degrees lower than expected just because of the snow. The computers don't always account for this. I could talk forever about this so I'll stop here. Most of the time I find going outside and looking is the best way to see whats going on. Just a few of my cents. -Alex

Re:NOAA/NWS (1)

maxume (22995) | more than 7 years ago | (#17948370)

Going outside and looking? Ask at your local home center about 'windows', they'll know. Hint: not the operating system.

Summary (1)

DraconPern (521756) | more than 7 years ago | (#17946492)

Only trust 6 days forcast. Avoid MSN Weather.

Conclusion: Microsoft Sucks (How Intuitive!) (-1, Troll)

curmudgeon99 (1040054) | more than 7 years ago | (#17946532)

Slogging through this guy's admirable grasp of statistics, it appears that the intuitive solution is that MSN (Microsoft) is far and away the least accurate. Why does this not surprise? The company that brought us the blue screen of death, that brought us Hacker Heaven (AKA Windows) is wildly inaccurate.

What is your source? (5, Informative)

Lord Satri (609291) | more than 7 years ago | (#17946546)

(I work at the Canadian Meteorological Centre, but I am not a meteorologist myself)

One thing that struck me is the 'abnormal diversity' of weather information sources. In Canada, weather models are computed in one place, a ~1000 processors computer in a basement which does only one thing: forecasting weather (the constant real-world observations that are ingested are used to adjust the models). Only one 'real' source (of course, there's the american, british, french, etc. official forecasting models to which we compare 'scores' on a daily basis). However, there's plenty of other canadian websites which will give you weather forecasts (one example [meteomedia.com] ). From what I know, these "other websites" have a significantly smaller workforce of meteorologists to interpret the models results than the Meteorological Service of Canada [ec.gc.ca] (the CMC is part of the MSC). That's why I would favor the 'original' source instead of a 'second-hand' source. I must however admit, commercial online sources of weather forecasting sometimes offer value-added products, such as the number of ski trails opened, offer general weather information capsules, etc.

And by the way, the official Environment Canada weather website [ec.gc.ca] is the most visited website in Canada (or at least, that's what they tell us, the employees! :-).

Additional comments... (1)

Lord Satri (609291) | more than 7 years ago | (#17946608)

(the fact that you must post quick at Slashdot or your comment will be buried really lowers post quality since people (or at least I) sometimes rush their comments uselessly... ;-) Additional comments (after reading parts of TFA).

We must not forget online forecasting websites often offer a trend for a whole day, but (in Canada's weather office case, see parent) it is worthed to read the accompanying text to know how the weather will evolve throughout the day. If you need close to real-time observations, use radar information, such as this one for Toronto [ec.gc.ca] .

Also, one must be aware that global-scale models are computed at a "low" spatial resolution (one point every kilometer 33 km in Canada) (don't forget, those models run in real 3D, not in 2.5D, thus adding several points in the vertical axis). There are various higher resolution models which are also ran: in Canada (IIRC), the 'regional' model runs at a 15km horizontal spatial resolution. I underline this only because it is important to know that models at this time can't tell you the weather for your own neighborhood specifically. (I am however working on weather projects at the city-scale, 5m spatial resolution!!! but those models are run over an urban area on a need-to-run basis, computers aren't fast enough for meteorologists ;-).

Re:What is your source? (1)

mgblst (80109) | more than 7 years ago | (#17946746)

It always seems a bit odd to me, that when you model the weather, you need to model the entire world, and all the different models get their data from the same sources. Why then, don't we have a world weather computer? What I mean, is combining all these different computer resources into one huge model? I know that each nation does its own little tweaks to produce the "best" model, but surely the ability to throw even more machines at such a problem would produce better results? Are we heading this way, or is their just too much prestige for a country to work out its own weather?

(And surely in Canada, you could just steal the results from the USA equivalent)

Source Integrity (3, Informative)

wasted (94866) | more than 7 years ago | (#17947052)

It always seems a bit odd to me, that when you model the weather, you need to model the entire world, and all the different models get their data from the same sources. Why then, don't we have a world weather computer? What I mean, is combining all these different computer resources into one huge model? I know that each nation does its own little tweaks to produce the "best" model, but surely the ability to throw even more machines at such a problem would produce better results? Are we heading this way, or is their just too much prestige for a country to work out its own weather?


One reason for countries to maintain their own weather forecast agency is to ensure the integrity of the data. This ensures that a country isn't receiving tainted data, or denied data. Models could be skewed to favor accuracy in one country over another, giving that country agricultural and energy trading competitive advantages. During many conflicts, countries where the conflicts occur cease dissemination of weather data so that the opposing force can't use the data. The US DoD maintains its own weather forecasting computers to ensure that access can't be denied, even if there is an NWS outage. If a country maintains its own systems, data integrity isn't in question.

A reason to use multiple models is that each model has different strengths. One model may tend toward forecasting precipitation over the midwest more often than it is likely to occur, and another may tend to forecast precipitation less often then actual. By using both models, we can get a better idea of the actual weather. In this case, if both forecast dry, it would likely be dry, and if both forecast precipitation, we would expect precipitation, and if they split, the forecasters would have to go back to old time forecasting techniques and get the coin and dartboard out. (Just kidding about the coin and dartboard. They'd really have to unfold their broaches, hats, and Pterodactyls, and start using the charts for what they were intended.)

Re:Source Integrity (1)

mgblst (80109) | more than 7 years ago | (#17947434)

I spoke to someone about this last year, and I was led to understand that their was a huge pool of data, colleceted by all the weather agencies around the world, and everyone had access to it. It is not like Canada has weather recording stations spread throught the world, in case they don't get data from somewhere.

Re:What is your source? (1)

Lord Satri (609291) | more than 7 years ago | (#17947106)

"Why then, don't we have a world weather computer?"

Read my other comment [slashdot.org] . There are several reasons. One is that models runs at higher resolutions for specific regions. i.e. Canada runs higher resolution models over Canada, a thing which, obviously, France or Britain won't do. There are also numerous products (e.g. marine, aviation, emergencies, etc.) which are more or less region-specific (or that no one wants to produce for the whole world).

There are countries, Australia is an example, which decided to partner with another 'big' country for their weather forecasting products instead of having to run their own at a great cost.

That said, maybe I'm too much an optimist, but things are being more and more interoperable and there is more and more collaboration between international weather centres. There will be a need for multiple 'weather computers' for a long time, but general efficiency/collaboration is definitely going up.

Re:What is your source? (1)

FuzzyDaddy (584528) | more than 7 years ago | (#17947344)

"climate [aesto.or.jp] is what you expect. Weather is what you get."

-Mark Twain

Re:What is your source? (1)

cheater512 (783349) | more than 7 years ago | (#17947430)

Dont you mean the USA could steal the results from Canada?

Re:What is your source? (2, Interesting)

Anonymous Coward | more than 7 years ago | (#17947146)

The fun part.... My personal weather station is only lacking radar, I do have old slow scan satellite imaging from a ham radio receiver. and I can predict weather at my location far more accurate than the NWS and the local stations.

By looking at the rate of barometric pressure drop and the rise in humidity and wind changes I can tell you within a 1/2 hour when it will rain or storm and typically how badly.

What blows my mind is why does the National weather service not install a crap load of cellular connected mini weather stations across the country in the military grid coordinates? it would give them a ton more data to parse to increase the accuracy of the predictions.

The fun part is when I go to some of the local media functions and start talking to local weather experts with their PHD in weather science I talk about my observations and what I notice in trends and they crap their pants when I tell them MY pc is running software I wrote to do most ofthe work for me and no I do not have a degree in weather science.

Re:What is your source? (3, Funny)

CmdrGravy (645153) | more than 7 years ago | (#17947538)

Within half an hour ! That's pretty gosh darn impressive work there sir !

If you wouldn't mind going into a bit more depth I'd love to hear the details of how you knock up these forecasts, at the moment I can only predict the weather for definite maybe 20 - 25 minutes ( using basic optical observations ) in advance and I'd love to shave off those extra 5 minutes but I wonder if it's worth the cost of investing in something like a PC. I've seen portable weather stations you can install in your living room from hippy shops, do you think these would be suitable ?

Re:What is your source? (1)

geoffspear (692508) | more than 7 years ago | (#17947586)

What blows my mind is why does the National weather service not install a crap load of cellular connected mini weather stations across the country in the military grid coordinates?

Lack of an unlimited budget?

Who knows what they'll be able to accomplish now that Rick Santorum isn't around to try to prevent them from competing with PA-Based Accuweather anymore, though?

Re:What is your source? (1)

Helios1182 (629010) | more than 7 years ago | (#17947628)

Sites like http://www.wunderground.com/ [wunderground.com] take in feeds from small weather stations (schools, homes, etc.) and display them in a list. At least in Chicago there are enough to get a good idea of the real weather (not just at O'Hare).

Reliable forcasting method... (5, Interesting)

AmIAnAi (975049) | more than 7 years ago | (#17946558)

I remember some years ago a radio presenter saying that you could achieve greater accuracy than supposed weather forcasters simply by using the assertion: today's weather will be the same as yesterday. Have we moved on from this position?

Re:Reliable forcasting method... (1)

cosmocain (1060326) | more than 7 years ago | (#17946650)

fact is:

a = forecasted weather
b = actual weather
c = variable, which determines the need for an accurate forecast of a nondescript person.

the larger "c" is, the more will "a" and "b" differ.

but wait...
... you really can rely on that, duh.

Re:Reliable forcasting method... (4, Informative)

Bob(TM) (104510) | more than 7 years ago | (#17946686)

In the forecasting vernacular, that method describes forecasting based on "persistence".

Persistence is the yardstick all forecasters use to determine if they should find another line of work (or be asked to do so by others). If you can't demonstrate an understanding of the processes and data such that extend beyond the data source everyone else has (ie., the weather their experiencing), it's just snake oil.

(IAAM)

Re:Reliable forcasting method... (5, Informative)

Anonymous Coward | more than 7 years ago | (#17946840)

persistence is 75% reliable.

On any significant sample, weather reports were never worse than this.

Currently, models are able to make 85% or a little more accuracy.

This may sound paltry, but where this really works out is in longer term forecasts. At 75% you are probably wrong at 3 days forecast. Even if you take the assumption that forecasts are independent from day to day, 85% means you are probablt wrong after 5 days.

The extra two days you can predict for is what the money is going towards.

Re:Reliable forcasting method... (2, Funny)

OldBus (596183) | more than 7 years ago | (#17946980)

persistence is 75% reliable

Won't this depend where in the world you are? E.g. in desert areas most days are likely to be hot and sunny. Here in England, we consider stable weather for 10 minutes to be persistent.

Re:Reliable forcasting method... (1)

n0rr1s (768407) | more than 7 years ago | (#17946998)

Ha. Five minutes ago there was no rain. I read your comment, looked out of the window, and now it's raining.

Yes, I'm in England too.

Re:Reliable forcasting method... (1)

KevinColyer (883316) | more than 7 years ago | (#17947246)

I used to live in Plymouth and I used an inverse model of persistence: if it is raining this morning it will be dry later or visa versa. I used to feel I had a high degree of accuracy!

I still took my coat with me whenever!

Re:Reliable forcasting method... (1)

CmdrGravy (645153) | more than 7 years ago | (#17947570)

It's kind of sleeting here at the moment, the question is will it get colder and turn into snow necessitating an immediate retreat from work or will it get warmer and turn into boring old rain.

Re:Reliable forcasting method... (0)

Anonymous Coward | more than 7 years ago | (#17946970)

That radio presenter didn't live in Michigan.

Re:Reliable forcasting method... (1)

edremy (36408) | more than 7 years ago | (#17947398)

Persistance is a great way to do it, except that the information out of it tends to be pretty much useless. Think about what you care about- temperature/humidity and preciptiation. Frankly, I don't care so much about these if they continue the way they are right now. It's cold and clear outside right now, but I'm dressed for cold+clear. If it was rainy I'd have an umbrella, if it was really snowy I'd have driven my wife's Subaru to work.

What I care about (for lack of a better term) is the weather delta. When will it *stop* being cold and clear? That's when I have to change my behavior- bring an umbrella for when it starts raining, ditch the jacket, etc. I almost got stuck on my way home the other night since I didn't pay attention to the forecast and assumed persistance- cold+clear turned into slick snow. The forecasters got that right, persistance didn't.

Huh (1)

chuckymonkey (1059244) | more than 7 years ago | (#17946578)

Someone used math to prove that the weatherman is wrong or maybe even right. Who'd a thunk it.

rain? (2, Interesting)

Shooter6947 (148693) | more than 7 years ago | (#17946584)

What about predictions for precipitation? The author claimed that he was motivated by a washed-out waterpark visit. Variations in the high temp by 3 degrees don't really matter a lick -- what matters is if it predicts sun and you get rain, or vice versa. How accurate are those "20% chance of rain" predictions really? Inquiring slashdot readers want to know!

Re:rain? (3, Interesting)

Wordplay (54438) | more than 7 years ago | (#17946658)

You'd need a lot of data for that one, if you want to establish the accuracy of the probabilities. Unless I'm missing a more mathematically clever way to do it, I'd assume you'd require lots of 20% days to determine whether rain happened on anything near 20% of them. Similarly, 10, 30, 40, 50, etc would require their own groups of lots of days.

It'd be even trickier in, say, the SF Bay Area, where it only rains for two or three months a year, and then almost every day. Your 0% and 80-100% groups would be well-stocked, but not so much the other ones.

Re:rain? (1)

msbmsb (871828) | more than 7 years ago | (#17948028)

Plus, you'd have to do some interesting things regarding localized precipitation. Would a 20% chance of rain for a metropolitan area be fulfilled if it rained *anywhere* in the covered area, not just where you are sitting taking down readings? If it rained a mile away from a person who checked the weather to find a percent chance of rain, but not in their exact location, it still rained for that forecast area. Would it make sense in that case to consider the chance of precipitation as the chance for any given location, i.e. 100% chance of scattered precipitation over the whole area with a smaller percent chance of it being in a precise location? This would take some thinking to really get right.

Re:rain? (1)

jlf278 (1022347) | more than 7 years ago | (#17948038)

You do need lots of days. Even if the groups 0%,10%,20%,30&40%,50&60%,70&80&90% and 100% had ~52 days each, you'd have a decent degree of error. However, in SF Bay, you say most days are 0% or 80-100%. Aren't these really the only days of practical interest? Does it really matter how accurate a 50% prediction is, if it is 37% or 58%? If the yes rain vs. no raingroups are so well stocked (150+ days say), then that makes things all the easier. Although one interesting and simple calculation would be overall accuracy, by multiplying the sum of percents in a year (say 32%) by 365 and subtracting the number of days it rained during the year (easy to find). And if you were really crazy you could look at how accuracy for no rain vs. rain improves (supposedly) as the predictions go from 10 days out, to 9 days, to 8 days, etc.

I want one of these for stock analysts. (2, Interesting)

Anonymous Coward | more than 7 years ago | (#17946598)

Anyone know who tracks the accuracy of individual stock analysts?

Re:I want one of these for stock analysts. (1)

Sean5033 (246214) | more than 7 years ago | (#17947320)

The Motley Fool (www.fool.com) has an area where they track Jim Kramer's success rate.

Re:I want one of these for stock analysts. (0)

Anonymous Coward | more than 7 years ago | (#17947474)

But remember! Past performance may not indicate future results!

The "PC GUY's" version of fun (1)

PoliTech (998983) | more than 7 years ago | (#17946602)

For some reason looking at all of those spread sheets and bar charts, I kept picturing the PC Guy from the MAC television advertisements.

PC is a excitedly showing off all of his charts and graphs.

With the Mac Guy looking on from the side with a slight smile...

Re:The "PC GUY's" version of fun (1)

Overzeetop (214511) | more than 7 years ago | (#17947000)

That's because the Mac guy just looked out the window and saw that it was raining and decided to cancel the picnic while the PC guy went outside to eat soggy sandwiches and get soaked by the afternoons "partly cloudy" weather.

I believe it was a DC forecaster who once said "I just shoveled 8 inches of partly cloudy off of my driveway" after missing the forecast the day before. It pays to have a sense of humor when you're in the meteorology business.

Statistics don't lie Statisticians do! (5, Informative)

wesborgmandvm (893569) | more than 7 years ago | (#17946616)

Kudos to this guy for the work he put into the effort but it is really comparing apples and oranges. A forecast is a time sensitive product. You can't look at the forecast provided on day x from two different sources and compare them unless the forecast was provided at the same time of day.

The National Weather Service collects all the weather data used by forecasters, they also provide the 1st forecast. AccuWeather and others take the National Weather Service forecast then watch the new data (using National Weather Service provided data) to offer a refined forecast a few hours latter. Who do you think is going to be the most accurate the guy who provides the first forecast or the guy who waits for more data and then refines the for cast? AccuWeather's has statistics that show they are more accurate then the National Weather Service but if you used the AccuWeather forecast then waited for the next National Weather Service update I bet National Weather Service would be more accurate.

I am surprised that this guy used the weather.com and not the National Weather Service for the actually temp for all his calculations. (It doesn't matter b/c I am sure weather.com is right from National Weather Service data). He did point out that AccuWeather is the only one who provides forecasts > 10 days in advance.

My preference for weather forecasts is:

National Weather Service
AccuWeather (easy to understand graphics and 2 week forecasts)
The Weather Underground (Years ago they were the1st to provided free access to hurricane computer models)

Re:Statistics don't lie Statisticians do! (1)

TapeCutter (624760) | more than 7 years ago | (#17946888)

"He did point out that AccuWeather is the only one who provides forecasts > 10 days in advance"

He must have missed Australian seasonal outlooks [bom.gov.au] .

Re:Statistics don't lie Statisticians do! (4, Insightful)

Overzeetop (214511) | more than 7 years ago | (#17946974)

Actually, you're only considering the accuracy of the scientific forecast. That is essentially useless to the end user - what they (I) want is accuracy of the reported forecast. The difference? I don't care when the actual prediction was made, I want to know that when I look at the forecast, it is likely to be correct. A very accurate forecast that is only updated once every three days is not nearly as useful as a farily accurate forcast updated every ten minutes. The former would be the best by your yardstick, but wouldn't necessarily help determine if the likilihood of a hail storm was high for this afternoon as much as the latter.

Re:Statistics don't lie Statisticians do! (0)

Anonymous Coward | more than 7 years ago | (#17947598)

I'm surprised he used weather.com for his temperatures too.

I'm from western NY state originally. Now that I've moved away, I'm learning to call my parents and ask them what the weather's going to be like when I plan to drive up that way, because weather.com will almost always be wrong. (I can say this since weather.com's 30% chance of snow in Buffalo on Tuesday had me driving through whiteouts and icy roads for 3 hours. Should have called the parents even if it was before 7 a.m... They knew the lake effect was coming.)

Personally, I don't care that much how close temperatures are. I'd just like to avoid repeats of that, which seem to happen a lot more than I'd prefer in the Northeast.

Can we believe the forecasts? (4, Insightful)

gavink42 (1000674) | more than 7 years ago | (#17946622)

Personally, I take weather forecasts with a couple of grains of salt.

However, the last cold blast that came through Memphis was forcast almost a week ahead of time. Weather radar of the middle part of the country showed about 90% clear of storms. So, I had a hard time with that one.

To my surprise (and right on time), down came the blast of cold air. Soon after was the promised snow/ice.

It still seems like an inexact science... with a touch of art and a pinch of luck thrown in for good measure.

Re:Can we believe the forecasts? (1, Insightful)

Anonymous Coward | more than 7 years ago | (#17946742)

Replace weather with climate and see the responses. We seem to trust climate predictions more than weather predictions, when both are inherently and historically inaccurate.

Re:Can we believe the forecasts? (1)

BootNinja (743040) | more than 7 years ago | (#17946886)

What I find funny is that the entire practice of weather prediction is based on a logically fallacy. They take the data from previous years and say, ok, last time conditions looked like this x happened, so we predict x will happen again. Anybody who's taken an introductory logic class knows that you can't correlation does not equal causation. Plus, we've only been studying the skies for about a hundred years, so we don't have enough data to make a decent correlation in the first place.

Re:Can we believe the forecasts? (5, Insightful)

Daniel Dvorkin (106857) | more than 7 years ago | (#17947160)

What I find funny is that the entire practice of weather prediction is based on a logically fallacy. They take the data from previous years and say, ok, last time conditions looked like this x happened, so we predict x will happen again. Anybody who's taken an introductory logic class knows that you can't correlation does not equal causation.

And anyone whose understanding of correlation goes beyond "an introductory logic class" knows that in fact, as long as you're very careful about what you're doing, you can in fact very often use observed correlations to make valid predictions.

There's this whole field of study called "statistics," see. Not the "X% of people surveyed believe Y" type of thing you hear on the news, but an actual science, grounded in rigorous mathematical theory and growing more sophisticated all the time at producing useful knowledge from mountains of data. People get PhD's in it and stuff. Really. Maybe you ought to read about it some time. Maybe even take a class.

Or perhaps you'd rather remain secure in your prejudices, repeating "correlation does not equal causation" like a mantra, snickering at people whose knowledge you choose not to understand.

Re:Can we believe the forecasts? (0)

Anonymous Coward | more than 7 years ago | (#17947188)

They take the data from previous years and say, ok, last time conditions looked like this x happened, so we predict x will happen again.

Almost completely wrong. They take current conditions/observations and then use the physical sciences of how an atmosphere behaves to produce a numerical model [noaa.gov] of what the atmosphere would look like. Run a bunch of different ones of these and compare the results and you have an "ensemble".

Now, add in historical statistical data to the numeric data and you get a statistical model [noaa.gov] . In the shorter time frames, the statistical models are often the most accurate and often can match or beat the human generated forecast.

Re:Can we believe the forecasts? (0)

Anonymous Coward | more than 7 years ago | (#17947420)

What I find funny is that the entire practice of weather prediction is based on a logically fallacy. They take the data from previous years and say, ok, last time conditions looked like this x happened, so we predict x will happen again. Anybody who's taken an introductory logic class knows that you can't correlation does not equal causation.


Anyone who's taken an introductory engineering course knows that correlation approaches causation for sufficiently high levels of correlation.

And anyone who's taken an introductory philosophy course knows that logic is just an invention of human thought, and physical systems are by no means required to obey our flawed and imperfect sensory impressions and the deductions we make from them.

Re:Can we believe the forecasts? (3, Funny)

nomadic (141991) | more than 7 years ago | (#17946832)

To my surprise (and right on time), down came the blast of cold air. Soon after was the promised snow/ice.

I remember when a year and a half ago one of the hurricanes was in the Gulf of Mexico, heading almost straight west, and the meteorologists all insisted that the hurricane would make a complete 180 degree turn and head back east and smack into Florida. I didn't believe them. On more than one occasion I publicly stated that this was ridiculous.

I ate a lot of canned food that week.

The trouble with Miami/Ft. Lauderdale News ... (0)

Anonymous Coward | more than 7 years ago | (#17947850)

Ever since Hurricane Andrew, the S. Fl forecasters (the ones working for the news channels) have made a bad habit of "bending" the cone of strike probability such that 100% of the tropical storms/hurricanes that pass any closer than Bermuda are sure to hit Florida (according to these idiots).

And thanks to them, 100% of the storms do cause trouble - mostly due to all the panic they induce.

That's probably why when Hurricane Ivan did a "crazy Ivan" you were caught with your pants down - you've heard these fools cry wolf too often.

I've made it a policy to ignore the local forecasters regarding tropical weather. I look at the military forecasts and National Hurricane Center predictions instead.

Here's a thought for any S. Fl forecasters - stop bending the damn cones!

Re:Can we believe the forecasts? (1)

Mr2cents (323101) | more than 7 years ago | (#17946926)

Ever since I've been riding to work with my bicycle, I'm a big fan of online weather radars. You can see where it's raining in real-time and where the rain is heading. It's only predictable up to a few hours but many times that's all I need. It has kept me dry on many occasions.

Of course, if a rain zone develops right above your head you're out of luck. But most of the time, when it rains it's just an active rain zone passing over your head.

If you live in the Benelux, chek out http://www.buienradar.nl/ [buienradar.nl] . It's the best radar I found, with images only a few minutes old.

Oh, Slashdotters reading about science... (-1, Flamebait)

Anonymous Coward | more than 7 years ago | (#17946676)

You know if you're a slashdotter if you believe the "science" part of computer science.
This group is too stupid for this article.

Free forecast (2, Insightful)

140Mandak262Jamuna (970587) | more than 7 years ago | (#17946682)

These web sites provide these weather predictions for free, and it is worth every penny you paid for them. Compared to some other people in prediction business, tarot cards come to my mind, these sites are not doing that badly.

Whom (4, Funny)

mdsolar (1045926) | more than 7 years ago | (#17946766)

A preposition is awkward to end a sentence with. But, "whom" is the word "on" is followed by.
--
Solar follows the rules for grammer. http://mdsolar.blogspot.com/2007/01/slashdot-users -selling-solar.html [blogspot.com]

Re:Whom (1)

Icculus (33027) | more than 7 years ago | (#17947296)

Solar follows the rules for grammer

but spelling be damned!

Re:Whom (1)

mdsolar (1045926) | more than 7 years ago | (#17948270)

Here! Here!

Slashdot... Bringing down the web (1)

Devir (671031) | more than 7 years ago | (#17946770)

One site at a time.

Interpretation of the models is everything (5, Interesting)

Aliks (530618) | more than 7 years ago | (#17946794)

I am not a meteorologist, but I have worked with them a few times.

Generally the competing weather models will show a range of possible outcomes with various probabilities. You can average across all scenarios and come up with a 60% probability of rain, but the more days out you go more the scenarios diverge, so the less useful a single average will be.

Most people would not find it useful to hear that "there will be probably be thunder on Wednesday if it remains hot enough, but if it cools down on Tuesday then the thunderstorm will be off to the north somewhere"

Additionally, a lot of weather conditions are influenced by thin layers of cloud high up, so thin that precise measurements are critical so precise forecasts in one location more than 3 days out are difficult.

Re:Interpretation of the models is everything (1)

zizzybaloobah (1021731) | more than 7 years ago | (#17947472)

"Most people would not find it useful to hear that "there will be probably be thunder on Wednesday if it remains hot enough, but if it cools down on Tuesday then the thunderstorm will be off to the north somewhere"

Actually, I would find that kind of forecast helpful, but it certainly doesn't make a nice TV soundbites does it?

Just like when I purchase something on the internet, I check a variety of websites to see what the general consensus is, and then if I need more information, I always relay on the good old National Weather Service page (it is indeed nice that they don't serve up a lot of ads, but if you're using Firefox w/AdBlock, who cares).

I find the most useful link on the NWS page, is the 'Forecast Discussion' (found on the forecast page for what ever region's forecast you're viewing). It provides the exact kind of statements you put in your post. The terminology and abbreviations can be a little much sometimes, but you can still get the gist of what they're saying. The forecast discussion wouldn't be useful if you're trying to plan more than a day or so out -- I find it's best to use this page the day before or the day of your planned activity.

Possibly the best slashdotted error message ever. (3, Funny)

sammy baby (14909) | more than 7 years ago | (#17946808)

"Total Freaking Database Error!"

Best 500 error I've ever seen. (Although I'm not sure it actually sent a 500.)

YIC! (1, Funny)

Guppy06 (410832) | more than 7 years ago | (#17946818)

Where's the Wii Forecast Channel?

Re:YIC! (1)

tresstatus (260408) | more than 7 years ago | (#17947018)

As of the time i checked it at 7AM this morning, it was still telling me what the temperature was at midnight. I can assume that when i get home this afternoon, I can check the temp at 5 and it will tell me what it was at noon.

Re:YIC! (0)

Anonymous Coward | more than 7 years ago | (#17947102)

The Wii is smart.. It knows you aren't playing with your Wii enough, so it isn't staying up..up to date that is..

YOU FAIL IT. (-1, Offtopic)

Anonymous Coward | more than 7 years ago | (#17946844)

non-fucking-existant. Can reaLly ask of in 0ur group

PHEW! (1)

LoudMusic (199347) | more than 7 years ago | (#17946860)

I'm just glad MSN didn't come out on top. That would have ruined my day. Besides that, meh, it's an educated guess. So long as they can tell me "it's gonna be hot" or "it's gonna be cold", I'm cool with it. The weather forecasts for my area are almost always more incorrect than his findings, especially when it comes to precipitation.

Eh, at least they get the Moon phases right ;)

slashdotted! (2, Informative)

sid77 (984944) | more than 7 years ago | (#17946908)

so, here's the mirror dot link [mirrordot.com]

'statistic' and static weather forecasts (1)

Philzli (813353) | more than 7 years ago | (#17946928)

Ah I loved it: The first time I travelled to the US I rented a motor home and
drove through the grand canyon / national parks around it. And everywhere were
signs that told you that the motor home park / camping was already overfilled
with tourists at 9pm this morning, but once I risked it, I drove the 30 miles
from the sign to the park and found out it was empty. I asked a ranger about it
and he told me: You know, we have these signs since 30 years, the data is
based on a calendar that is even older...

They just recorded 1 or 2 years in a row when the park was filled and then made
a 'forecast'...

You can't fool mother nature (4, Funny)

TheHornedOne (50252) | more than 7 years ago | (#17946936)

I work for Mother Nature; So I am really getting a kick out of most of these replies. Some of you guys are very good at making it sound like you know what you are talking about. But trust me.... You don't. I think you just want to make yourself sound smart, when in reality you don't know what you are talking about. This is how bad info gets passed around. If you dont know about the topic....Dont make yourself sound like you do. Cos some slashdotters believe anything they hear."

/wrong metasite
//slashies
//dont' kill me

The Weather Channel has to be the worst (0)

Anonymous Coward | more than 7 years ago | (#17947008)

They're almost always wrong, even their current conditions aren't accurate.

Who cares about temp? Is it gonna rain? (2, Insightful)

Eideteker (641508) | more than 7 years ago | (#17947094)

I'd rather know if there's going to be any precipitation so I can plan my motorcycle gear correctly. Let me know when someone compares precip. forecasts.

Sorry to be a grammar nerd but... (1)

blubadger (988507) | more than 7 years ago | (#17947108)

"[The article] shows who's on target, and on who you probably shouldn't rely."
This just jars. Let's try again:

"[The article] shows who's on target, and who(m) you probably shouldn't rely on."

Re:Sorry to be a grammar nerd but... (0)

Anonymous Coward | more than 7 years ago | (#17947808)

"[The article] shows who's on target, and who(m) you probably shouldn't rely on."

On Slashdot, we don't end our sentences with prepositions.

Re:Sorry to be a grammar nerd but... (1)

iambarry (134796) | more than 7 years ago | (#17947840)

How about :
"[The article] shows who's on target, and who(m) you probably shouldn't rely on asshole ."

Re:Sorry to be a grammar nerd but... (0)

Anonymous Coward | more than 7 years ago | (#17947856)

Don't worry about the Grammar here the Articles are dumbed down to relate to the readers. 90% of the rodents here run Windows OS and pretend they run Unix or Linux one look at their spelling will tell you they have never been able to write a section of software code that works. And if they claim they have code out there it is in the Windows systems they are trying to use.

Re:Sorry to be a grammar nerd but... (1)

Jurph (16396) | more than 7 years ago | (#17947860)

Huh? Why change the word order? All he did was mix up "who" and "whom" -- there's no reason to compound his error by moving the preposition to the end of the sentence.

I did this in 8th grade. (1)

nharmon (97591) | more than 7 years ago | (#17947126)

My 8th grade science project was to see who could predict the weather the best. I collected forecasts and then compared them to actual meteorological conditions. I totally forget what my findings were but it is too bad Slashdot wasn't around back then, I could have had some great publicity. :)

My experience with the BBC weather forecast... (3, Interesting)

OneSmartFellow (716217) | more than 7 years ago | (#17947132)

for my area is that they are usually accurate down to a period of about 3 hours. As an example.

http://www.bbc.co.uk/weather/24hr.shtml?world=41 79 predicted that it would be snowing yesterday morning by 0600. Sure enough, I woke at six, and it was snowing. I awoke earlier in the night (about 0400) and it hadn't yet started.
Similarly, that site predicted that the snow would drop off by noon, and turn to sleet or rain by 1600. Again, this prediction came true, within an hour of the predicted time.

Generally speaking I find the BBC weather site to be accurate significantly more often than not (guesstimate 80% accuracy) with the 24 hour forecast being almost universally correct, and the 5 day forecast being the least reliable. (as expected)

This is a FAR cry from the weather predictions when I was a lad. Then the weather forecast on TV was simply a way to poke fun at the meteorologist, who clearly was doing the best he could, but invariably got it wrong.

Old saying (1)

markjo (977895) | more than 7 years ago | (#17947134)

Climate is what you expect. Weather is what you get.

Obligatory Stats Joke (3, Funny)

frank249 (100528) | more than 7 years ago | (#17947156)


Nice article but the sample only uses an 'n' of 14 days. I would have more confidence in the means, standard deviations and correlations if the author had used a bigger 'n'. For in stats, as in ethics, the n's do justify the means.

We got global warming down, why not the short term (2, Insightful)

lessthan0 (176618) | more than 7 years ago | (#17947222)

Since we can predict with absolute certainty what the weather of the Earth is going to be 100 years from now (latest IPCC report), why can't we accurately predict the weather 10 days from now? Unless maybe we can't predict the weather 100 years from now. Hmmm.

Re:We got global warming down, why not the short t (1)

tsbiscaro (888711) | more than 7 years ago | (#17947328)

Climate is different from weather. A climate prediction is based on long spatial scale, while weather can change within a few miles. So, it can rain in your house and not on 4 blocks away, and one cannot predict that.

IPCC is not telling how the weather is gonna be, but what is the temperature trend due to pollution/deforestation.

Also, inital conditions on numerical weather forecast models are crucial, and that's why some places have better forecasts (N hemisphere better than S hemisphere, 'cause SH is full of oceans and in loco data isn't available).

Re:We got global warming down, why not the short t (1)

EchoD (1031614) | more than 7 years ago | (#17947376)

That was my first thought when I read the report. Worse yet, the National Weather Service can't even get their advisories and warnings straight lately. I've had lake effect snow warnings expire without a flake falling. Makes you wonder if these weather stations are powered by rand();

Re:We got global warming down, why not the short t (1)

FhnuZoag (875558) | more than 7 years ago | (#17947458)

Man, I was waiting for one of these.

The answer is very simple. Because weather != climate. Climate is a statistical average over long periods of time and large geographical areas. (And we don't know with absolute certainty, in any case. Everything has to be qualified with error bounds, which is very obvious, really, because much of what will happen is dependent on what we will do in response to predictions.) Weather is localised temporary fluctuations in phenomena.

It's like saying that we can pretty much guess what the slashdot comments to a certain story would be saying, but it would be very unfair to ask us to type out the text of the Nth comment.

(Well, except for First Post, In Soviet Russia, I, for one, welcome our.... etc )

Re:We got global warming down, why not the short t (1)

lstellar (1047264) | more than 7 years ago | (#17947640)

This worth more than a "2." I heard Iran is using PS3s to predict the weather...

Observation data source/NWS forecast (0)

Anonymous Coward | more than 7 years ago | (#17947362)

Being picky. For the NWS forecast, he uses a point [noaa.gov] forecast for a 5 kilometer grid of downtown Houston (see the small map on the forecast page). If you assume he's measuring against observations made at Houston International - several miles north of town - and covered by a different [noaa.gov] NWS forecast point, could impact the accuracy of the NWS data. There can be quite a range in temperatures [noaa.gov] across the Houston area.

I wasn't able to find in the mirrored version of the article what stations in Houston he was using to compare the forecasts against.

I predict... (2, Funny)

monkeyboythom (796957) | more than 7 years ago | (#17947382)

very stormy weather for the poor website linked to in the TFA. I believe the outlook will be dark, followed by intense periods of slashdotting...

Forcasting (1)

Blade80 (416070) | more than 7 years ago | (#17947450)

Who ever has the better dart board wins.

Large metro areas (4, Informative)

Anonymous Coward | more than 7 years ago | (#17947656)

Geographically large metro areas -- especially those with hills or large bodies of water -- make a weather forecaster's job all the more difficult. The chance of rain may be higher on one end of town, but it's difficult for a TV or radio announcer (or a newspaper spread, for that matter) to present the distinctions clearly and quickly.

Too long ago, when I was an undergraduate taking Meteorology, we visited the weather department in a Twin Cities (MN) television station. The anchor on duty was pretty blunt: if there's a 100% chance of rain on one end of town and a 10% chance on the other end, the broadcast would distill that as a 55% chance of rain. He argued that it was the best his department could offer given the commercial realities of limited airtime and the mandate to serve the entire metro area.

Precip (1)

tank3544 (1017758) | more than 7 years ago | (#17948020)

For those that mentioned precipitation just a reminder on what the chance of rain means It DOES NOT mean the zip code you're looking at has a 20% chance of precipitation It DOES mean of the entire surrounding area of the zip code 20% of that area has 100% chance of precipitation This study falls under MEH, despite the hard work, because the most important part (precipitation) was left out. Especially considering it's winter and snow or no snow is a HUGE consideration for people to take.
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