Slashdot Mirror
Statistical Accuracy of Internet Weather Forecasts
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."
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".
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.
"Can't you see that everyone is buying station wagons?"
Only trust 6 days forcast. Avoid MSN Weather.
(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). 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 (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 is the most visited website in Canada (or at least, that's what they tell us, the employees!
Animoog.org
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?
Any sufficiently advanced bug is indistinguishable from a feature.
Someone used math to prove that the weatherman is wrong or maybe even right. Who'd a thunk it.
"Some books contain the machinery required to create and sustain universes."-Tycho
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!
Anyone know who tracks the accuracy of individual stock analysts?
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...
(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.
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
Animoog.org
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)
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.
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.
sed -e 's/Chuck Norris/Rajnikant/g' joke > fact
A preposition is awkward to end a sentence with. But, "whom" is the word "on" is followed by.s -selling-solar.html
--
Solar follows the rules for grammer. http://mdsolar.blogspot.com/2007/01/slashdot-user
One site at a time.
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.
"Total Freaking Database Error!"
Best 500 error I've ever seen. (Although I'm not sure it actually sent a 500.)
Where's the Wii Forecast Channel?
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
No sig for you. YOU GET NO SIG!
so, here's the mirror dot link
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'...
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
They're almost always wrong, even their current conditions aren't accurate.
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.)
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.
sic
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. :)
for my area is that they are usually accurate down to a period of about 3 hours. As an example.
1 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.
http://www.bbc.co.uk/weather/24hr.shtml?world=4
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.
Climate is what you expect. Weather is what you get.
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.
Today's vices may be tomorrow's virtues.
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.
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).
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.
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();
If I only had a moose...
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...
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 )
This worth more than a "2." I heard Iran is using PS3s to predict the weather...
art is science made clear. -cocteau
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.
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.
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!
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.
I was quite curious about weather forecast accuracy as well. So three years ago I started collecting weather forecasts from the primary providers (Accuweather, Weather Channel, NWS, CustomWeather, Intellicast, etc.) and comparing them to actual observations. It's tougher than you might imagine, and there are a lot of factors that need to go into creating usable verification statistics.
I have a public site with some statistics for about 800 locations in the US available at ForecastAdvisor.com. There is also a blog with more in depth analysis (like how do temperature forecasts fare relative to how deviant the actual temperature is...in other words how well do forecasts do the further away from normal the actual is, and how to forecasts fare the further out they forecast for, and how does forecast accuracy compare over time.).
ForecastWatch.com is used by meteorologists and professionals. Accuweather, The Weather Channel, and several private meteorological companies use this system to help them understand and improve their weather forecasts.
And a geek note: ForecastWatch.com runs on Quixote (a Python web framework), while ForecastAdvisor.com runs on Ruby on Rails. The back-end forecast and actual collection, and calculations are Python with a MySQL database. Both sites are close to migrating to Django, a new Python web framework and ORM.
-Ace
As, in NOAA???
I've always wondered, but never had the time nor determiniation to find out, whether weather forecasts are more or less accurate than coin tosses and dice. I've always wanted to run an experiment similar to this :
;)
Take the 5 day temp forecast from a national weather site (NWS/weather.com, etc) and write the high / lows on one row.
Then, flip a coin and roll a single die.
Start with yesterday's high and low.
If you toss "heads" then add the number rolled on the die to the high temp for that day. If you toss "tails" then subtract. Do this for high and low temps for each of the five days.
Repeat this routine for a while, logging actual temps, then, after a certain amount of time. Compare your "forecasts" to the NWS / weather.com forecasts.
I've always wondered which would be more accurate.
Maybe this guy would run that test!
In Calgary, the weather forecast is just a suggestion. Actual weather can change 20C up or down in a few minutes. One side of the city can have snow and the other side sunshine. Sometimes it snows in July. So I have no idea why all these other wimps are complaining about a thunder shower on a forcasted clear day. I mean, what is the problem with that? The guy should be glad that he didn't get a heat wave followed by 2 feet of snow after the thunder shower...
Excuse me, but please get off my Pennisetum Clandestinum, eh!
It's the same reason why you can't predict what you might win if you play a slot machine for an hour, whereas the casino can predict the annual profits from its slot machines to a high degree of accuracy.
... and shows who's on target, and on who you probably shouldn't rely.
If you're going to make yourself sound snooty by not ending your sentence with a preposition, you should probably also use the object form of the pronoun 'who'.
My
If you want to know what the weather is doing...at least in North America, the National Oceanic and Atmospheric Administration's website is my favorite place for getting weather related info. There is no "fear mongering" like what is found on the network news. If it's going to snow, they say "It's going to snow." and then they tell you how much and let you freak out all on your own. They aren't about the fluff like The Weather Channel with thier silly shows and travel planning. NOAA's website even has tide schedules and nautical charts. That may not be important to most people but try planning a fishing trip with weather.com and you'll see how nice NOAA's website really is.
Personally, I could care less if some weather website is off by +-5 degrees for a high temperature tomorrow. I'm more concerned if we're going to get dumped on by a foot of snow during the Winter, or experience possible tornado spawning storms in late Spring. And I'm sure people around the gulf coast are more concerned about the latest hurricane than whether it will be 85 or 90 degrees on Wednesday. This is a great examination of predictions, and well thought out, but I think people are more interested in precipitation than temperature.
Reviewing just the first hour of video games.
That's a nice piece of work?? Looking at his charts, I'd be amazed if there was p0.1 significance to any of the differences, much less p0.05. Not significantly different. And sampling bias out the kazoo-- whatever differences there are in models are likely to be very different over areas with different weather and different times of the year. This would be like looking at the arrivals/departures board at your local airport, and deciding based on that which airline is most reliable.
Not to mention, the guy's inspiration for this was an unexpected storm-- but his analysis is limited to only hi and low temps???? Kind of like looking at the airport arrival/departure time board to decide which airline is most reliable in delivering luggage, isn't it? Excel will let you chart anything you want, but please don't try to pass it off as statistics.
1984 was supposed to be a warning, not an instruction manual.
When I did SAR in Alaska, a good weather forecast was essential. It didn't take long to realize that every source for information analyzed their data differently and came up with slightly different conclusions. The solution? Learn to forcast yourself. Learn to read an isobar map, learn to predict wind/temp/precip for your local area and you'll get a far more accurate feel for what's going to happen than any regional analysis could give you. Practice locally - you'll learn what worked and what didn't, then apply it to other locations. When I went to a friends wedding in Minnesota, I was able to predict when the rain would start to within 5 minutes - just enough time for the outdoor ceremony to be performed.
He who would be a man, must be a nonconformist. -- Emerson
To get a grasp of where the forecast is coming from, you first need to read the NWS forecast discussion for your local area. It tells you what the weatherman is really thinking
Second for the long range, look at the NWS Spaghetti Maps, which can give you a true appreciation of how consisitent the models are, the difficulty in making a prediction, and an advance warning of what may be coming your way
First off, the predicted temperatures take into account many factors, and try to come up with a low-precision laymans "flagpost", useful for someone who doesnt want to understand what makes up a weather system or event. So this analysis based on a low-precision value is falsely presenting an "evaluation", as the resulting precision is closer to 1-10 degrees at best.
Second, yes most of the data comes from NOAA/NWS. Using anything else for the highs/lows means not using the accurate tools that the forecasters us, particularly the comment about sometimes not getting the data until 5:00pm.
Third, I live in Houston, and no-one is accurate about this stuff.
Lastly, to get a much better idea about what is going to happen, go to NOAA/NWS at http://www.srh.noaa.gov/
use your zip code, and get your local page. Then scroll down the page and find "Hourly Weather Graph" under "Additional Forecasts and Information."
Here you get the next two days worth of data, updated hourly, and several pieces of information you should be using to "plan your day". If the temperature drops about the same time that the wind shifts, a front is coming in. If the dewpoint converges with the temperature, expect fog. Start watching THIS tool, and you'll be much less surprised. You'll never get true accuracy, but this picture can at least suggest likely variations. And before you use excel to graph things, find out what you're graphing.
Somebody better write them an email and tell them they have a bug on their website!
For some reason, they have alway given me a 7 day forecast.
Oh, and by the way, they also give credit to where they get their forcast from:
http://www.nws.noaa.gov/ndfd
Well, that might be true is some (most?) places. But:
In Winnipeg (which I just moved away from a couple months ago) can have violently different weather day to day and even sometimes within the same day. It as explained to me as: there are different "spheres of influence" when it comes to weather patterns and Winnipeg sits on the boarder of two of them. Knowing that weather is never stable means that this "line" constantly moves, sometimes quickly. Thus, the violent weather patterns.
In fact, in Southern Manitoba when farmers got together for the longest time (still?) they of course asked "How's the weather?". This was/is-n't just simple pleasantries. They were actually getting a reading on weather patterns because it although it might have been raining on one farm, on another one (just a mile down sometimes), it might not have been.
So basically, it isn't nor has it really ever been true for everyone.
Weather guessers here are rarely, if ever accurate as the mountains and Palmer Ridge play havoc with the weather. This caused me to ask, If his reference is flawed, then would the entire report be flawed?
The Weather Underground has numerous (4) weather stations in my zip code and they are usually right on top of each other regarding wind, temperature, barometrics, humidity and such. While the Weather Underground may not have the future down pat, their current readings are usually the most accurate I've found since these are weather stations where I live that are on line and reporting in near-real-time.
I would have liked to see the same report using other services as the reference to achieve some sort of correlation to his report. Maybe NWS, NOAA, Unisys or at least one more.
Another thing I do is bring up the NOAA maps in loop mode so I can see the direction of cloud travel, density and other things that may give an indication for short-term weather changes.
We get tons of lightning around here in the summer so this kind of accuracy is important around here. One source for lightning probability: http://www.nws.noaa.gov/tdl/radar/SW_probltg.gif. There are other lightning sources that can show current and recent past (1 hour) lightning strikes by type and frequency and on a map (see Strike Star network. Some individuals even have Boltek lightning monitors running with StormVue software on the net.
Interesting report. Questions still exist.
Banjo - The more I know about Windoze, the more I love *nix
as a farmer/ stockman and also being self employed in a business that is affected by weather, i know all too well that i need the most accurate forcast possible, with the least hassle. intellicast is available to me quickly, and i am satisfied with the results i get. but in texas, it is true that if you do not like the weather, just stick around for a day...it will change (smile)
"you may disagree with me, but i would lay down my life to defend your right to do so..."
I wonder how accurate their average forecast was.
"...the crowd at a county fair accurately guessed the butchered or the "slaughtered and dressed" weight of an ox when their individual guesses were averaged (the average was closer to the ox's true butchered weight than the estimates of most crowd members, and also closer than any of the separate estimates made by cattle experts)."
Or further, if you were to find weights that minimize their weighted average prediction error, in a training period, how much better would that prediction be?
"Follow me" the wise man said, but he walked behind.
The KNMI (Koninklijk Nederlands Meteorologisch Instituut), our offical government-sponsored weather forcast service screwed up royally yesterday.
They predicted a snow-storm for yesterday. Enough snow to completely disrupt the whole country. Weather-alarm!!!
The only thing that happened is that they scared a lot of people into staying at home, or go home early. The evening rush hour therfore had a max total traffic jam of only 12km. Instead of the normal 250km!
Oh, and indeed streets were white for a couple of hours. But the snow was gone before nightfall....
I will bet that people will not heed their advice as much the next time they sound the weather-alarm.
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.
You're confusing climate and weather. I can tell you from my observations of the climate that it will be hot and sunny in Sacramento on July 18 2007, but I can't tell you if it will be 90 or 115. Climate prediction is about determining the range of temperatures (or amounts of cloud cover, precipitation, etc.) that weather forecasts will fall into, not about determining the temperature on a specific day. People who have made far more extensive and more detailed observations of the climate have observed that temperatures are increasing and that this seems to be related to increasing levels of atmospheric CO2. Beyond just these empirical observations, they have identified an experimentally verified mechanism by which increased CO2 levels should increase temperatures and have created detailed models of this mechanism operating as part of the complex system of the atmosphere. These models predict that the climate in most places on earth should get warmer. I don't see why inaccurate short term forecasting should be much of a problem. You're trying to solve different types of problems, which yield to different analysis techniques.
I like my beverages with warning labels!
I wish I had this much free time.
a 0% chance of this dude getting laid in the next 10-14 days
I don't know about the rest of the world, but here in Portland, "20% chance of rain" does not mean that rain should be expected on 20% of the days with that forecast. It means that it will rain for 20% of the day.
The forecasters here are also fans of synonymous statements. Check out this week's forecast:
Fri: Mostly cloudy with a chance of rain
Sat: Showers likely
Sun: Occasional Showers
Mon: Rain and scattered sunbreaks
Tue: Scattered showers
Wed: Possible morning mist followed by afternoon drizzle
Thu: Sunny and 85 in the metro area. 30 with 6 inches of fresh powder on the mountain.
(They like to be wildly inaccurate every now and then just to piss us off. It will actually be 45 with possible light precipitation. Check the Portland evening news on Thursday to see who's more accurate: me or the weathermen).
I have been weather scraping daily since Feb. 2003
http://www.weatherreportcard.com/
Raisinettes are my raison d'etre
Here is one strong recommendation from the article:
"Accuweather was the clear leader in anything greater than 10 days in advance, being the only site providing a weather forecast."
And here's another gem of a conclusion:
"In addition to the above observations/recommendations, it was clear from the correlation analysis that the further removed a weather forecast is, the less accurate it will likely be."
I believe there's a very confusing error in the captions for tables 4 and 5 in the article, indicating rank. The captions say "higher is better" but it should be "lower is better". 1=best (green), 10=worst (red). Tables 6 and 7 do not say, but use the same numbers and colors, and lower is better there also. The article could have been more comprehensible if all the tables had indicated what's good and what's bad (tables 6-12 do not), not to mention done so accurately.
Somewhat obliquely related, I agree with frank249, that 14 days is not a statistically significant sample. How about a year.
Irony: a gorgeous inaccurate article about gorgeous inaccurate weather sites.
Bob Stein, http://bobste.in
If you look at the archive for May 31, 2004,
the forecast map seems to have indicated a risk for thunderstorms
in the area for that day.
http://www.hpc.ncep.noaa.gov/noaa/noaa_main.html
First, how forecasts are generated. All forecasts are a result of numerical weather prediction. There are around a dozen different models in operation around the world, and most of that data is retained by the operators of the models (usually the national forecasting office). However, all data from the US GFS model, operated by the NWS, released as works of the government are public domain.
What all the sites in this sample (bar the BBC) do is take the data files the GFS produces and reprocess them into a webpage. No human is involved at any stage. (The BBC get their data feed from the UK Met Office).
As the models only produce data points for every 40km or so spatially and every three hours temporally all the sites interpolate to some extent to produce a point forecast. The GFS also runs four times a day but these sites might take all four runs or just one a day. Combined, that's why differences between sites exist in these results. Nothing else.
REAL performance statistics are available here and here.
I live close to the San Diego area, where one of the local weathermen dedicates a page to explaining local weather conditions and forecasts http://www.kfmb.com/weather/index.php. The guy bases his reports on simulations run at a computer at the Scripps Institute in La Jolla and on NOAA information http://www.wrh.noaa.gov/sgx/display_special_produc t_versions.php?sid=SGX&pil=AFD, proving to be close to 90% accurate in the years since I discovered his web page.
However, I don't know if weathermen in other cities are as thorough, but I will say that since I discovered the guy, I haven't used The Weather Channel or any other weather page, except when he's on vacation (and he does take about six breaks a year).
Lil' Thindime, lilting a lacrimose lament, krashes the kwaint konfines of Kokonino Kounty