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This winter's forecast: NOAA vs. the woolly bears

By: Dr. Jeff Masters, 4:32 PM GMT on November 09, 2005

The tropics are quiet again today, so let's follow up on yesterday's discussion about the long range forecast for the coming United States winter. Those of you outside the U.S. will probably be more interested in what the International Research Institute for Climate Prediction has to say for your country, and I encourage you to check out their excellent web site for their seasonal forecasts. Interestingly, they forecast that virtually the entire world will have average to much above average temperatures during the December-February period, with only two tiny pockets of slightly below-average temperatures in Australia and central Asia. This should keep the oceans at the near-record high temperatures for near year's hurricane season, helping fuel another round of more intense than usual hurricanes. In addition, El Nino is expected to remain in a near-neutral phase the next 6-9 months (same as for this year's hurricane season), which should result in a higher than usual number of tropical storms and hurricanes for 2006. Still, I don't think we'll see anything like this year's level of activity, which was a once-in-a-lifetime hurricane season. Dr. Bill Gray's team at Colorado State University issues their first forecast for the 2006 hurricane season on Tuesday, December 6, and we'll talk more about next year's season then.

As we discussed yesterday, the official woolly bear caterpillar forecast for the U.S. mid-Atlantic coast area was for a warmer than average winter. The official NOAA 90-day forecast for the upcoming winter, issued on October 20 by the Climate Prediction Center (CPC), disagrees, calling for equal chances of an above average or below average winter over the eastern half of the country, but a higher than average chance of a warmer than average winter over the western half of the country. How well has the official forecast done in recent years? NOAA rates its forecasts using the Heidke skill score, which is a measure of how well a forecast did relative to a randomly selected forecast. A score of 0 means that the forecast did no better than what would be expected by chance. A score of 100 depicts a "perfect" forecast and a score of -50 depicts the "worst possible" forecast. For the 90-day temperature forecasts issued 1.5 months in advance done in January through May of this year, the Heidke skill score was greater than zero for two of the forecasts, less than zero two of the forecasts, and about zero the other forecast. The Heidke skill score for 90-day temperature forecasts issued 1.5 months in advance has averaged 8 the past ten years (see Figure 1.) So, while there is some skill in forecasting what the winter will be like 1.5 months in advance, this skill is not much better than flipping a coin or relying on woolly bear caterpillars. Let's look at some examples from forecasts for previous winters issued at about this time of year. The 90-day forecast done in mid-October of 1999 for the winter of 2000 was awesome, with a Heidke skill score of 50. However, the 90-day forecast done in mid-October of 2000 for the winter of 2001 was horrible, with a Heidke skill score of -15.

Figure 1. Skill of the official 90-day forecasts issued 1.5 months in advance by NOAA's Climate Prediction Center. Note that the average skill is positive, but has remained flat the past ten years, indicating that our skill in making long-range forecasts has not improved.

Why do seasonal forecasts do so poorly? It's partially because our physical understanding of what controls the climate is so poor. It's also in large part due to the fact that the long-term weather is chaotic and fundamentally unpredictable by nature, and no amount of physical understanding will help us. So, pick your forecast: woolly bear, coin flip, NOAA--the three techniques have similar levels of accuracy. Or you can check out the predictions of Psychic Helane, who wrote me to say she had correctly forecast the impact of Hurricane Wilma on South Florida over one month in advance. Her winter prediction calls for "the north especially St. Paul, Minnesota and Upstate NY will see its worst winter in memory." If I were an energy futures trader, I would wait until I saw a longer track record for Helane's weather predictions. She is also calling for a "huge hurricane in Alabama" this month, which is a virtual impossibility, given that sea surface temperatures in the Gulf of Mexico are now less than 80F (26.5C), which is too cold to support a major hurricane. Go with the official NOAA forecasts, which a have a proven track record of some having a least a little skill compared to chance.

Jeff Masters

Winter Weather

The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

Reader Comments

First post,

As far as the huge hurricane in Alabama in November, normally I would agree with the good doctor, but this is the season of 2005. I still think Delta and Gamma are still out there..
Jeff.... My grandmother and my father both think 30 years ago before computers and high end weather prediction the forecasts were more reliable and accurate. Is there truth to this? All the computer models do reflect and state great errors. Do you guys still use gut feelings? And look at history? Just wondering.
Forecasters do use human input (i.e. gut feelings). They have to do this because they are looking at multiple models, which disagree with each other. So a human has to decide which model to believe...often they split the difference. Read your local forecast discussion (at the bottom of the forecast page on wunderground) to see what they are doing.

As for your grandmother and father, well, they are wrong. More information leads to better forecasts. No forecast will ever be perfect, of course.
Delta and Gamma may be out there, but they won't be hitting Alabama. Cold water plus late fall steering currents make that an absurd prediction.
Thanks for providing a link to worldwide weather
Thanks Doc! Hey all...
Hello everyone :-)
Pscyhics? I never believed in them, wouldn't they all be rich by now????
Yeah, for some reason physic powers never extend to lottery numbers, or even hot stocks...
rwd - if psychis were true, Id be living in CA with twins! Nope, don't think so.......
You know how odd moments of something that strikes you funny sometimes stays with you? Last year, after Hurricane Jeanne, my fiance and I were out trying to find gas and dodging various items of road debris in Port St Lucie Florida. We were going past a local Psychic's place of business, and saw that her sign had blow over, trees were down and roof was damaged. My comment - "gee, wonder why she didn't see that coming?" - referring to not having taken her sign down.
And, yes, same sign blew down during Wilma...guess she is 0 and 3, and I get a laugh every time I pass that sign.
lol, weasel. i don't think you even need to be a psychic to see that coming.
lol Weasel... What a joke.
Just like Stormy said yesterday... It is all up to mother earth! I wouldn't rule out anything just yet, lol..
Yep, Mama makes the rules round here...and she's allowed to change them whenever she feels, like if she wants a cane in Dec, we'll get it...Hopefully, she is tired and wants to sleep till next year.
I hope so!!
rmh9903 et al: as for pre-computer forecasting being better than now, might want to check out the definition "Weather" in Ambrose Bierce's "The Devil's Dictionary", in particular this, attributed to "Halcyon Jones":

Once I dipt into the future far as human eye could see, / And I saw the Chief Forecaster, dead as any one can be - / Dead and damned and shut in Hades as a liar from his birth, / With a record of unreason seldom paralleled on earth. / While I looked he reared him solemnly, that incandescent youth, / From the coals that he'd preferred to the advantages of truth. / He cast his eyes about him and above him; then he wrote / On a slab of thin asbestos what I venture here to quote - / For I read it in the rose-light of the everlasting glow: / "Cloudy; variable winds, with local showers; cooler; snow."
After reading the very interesting and informative winter forcast predictions Doc Master has put together I can't help but make the following comments. BTW Doc, Thanks for taking the time to put this info together for all to share.

It seems that in the eyes of most of the weather forcasting community Global Warming is a Fait ac compli. However, what I have always found curious is this same group (weather forcasters and climatologists) have not improved their forcasting - prediction accuracy beyond about 10 days. Dispite the aid of an ever increasing data base, more and more accurate data, satellites and the advent of powerfull computers, the forcasting abilities beyond a couple of weeks have not improved at all!

Of coarse, in observational science large scale changes (such as the proposed Global Warming) can be more obvious than mid and small scale changes. Even if you give significant weight to the potential large scale observability premise, it is still diffucult (for me) to belive or find the Global Warming predictions as credible.

If we look at past climate trends, say over the past 500 years we have seen several significant anominalies with life spans in the 20-50 year or longer range. The Maunder minimum of the late 1600's is a classic example.

What if such an event were to occur today? Would the techno crowd and politicians be forging policies to increase CO2 gasses? How about space missions to the sun designed to increase sun spot activity? Or declaring certain geographic areas as off limits?

I, am of coarse over simplifying and over stating the obvious. But if you apply the basic scientific cause - effect rules to the Global Warming predictions and assumptions it is easy to call the whole premise in to question. That is because of the near total failure in the fields of medium term weather forcasting accuracy and the very poor current understanding of long term climatology. The forcasting summary that Dr. Masters provides near the end of his blog today is amazing. Forcasting beyond a few days is no better than a flip of a coin. Think about that!

That reality is difficult to ignore. It make me really nervous to see Global Warming become a major political issue and see it accepted as truth. Caution and perspective are needed on this issue, not blind acceptance.

Dr. Masters ending comments and prediction acuracy comparisions, to me, really drive this point home. Interested in hearing comments.

speakerman et al. - as I understand it (I'm a Ph.D. oceanographer, but I work on biology not physics), global temperature is a relatively easy thing to measure, but translating that measurement into climate effects is difficult - too many variables. so we have trouble translating "global warming" (an observation) into predictions of "global climate change". I think some people use the words "global warming" in the sense of "global climate change", which may add to the confusion. example: global warming may melt enough north polar ice to push the Gulf Stream south, or even stop it - which would whip more cold air into New England and lead to a local ice age. If ... if ... if ...

see what my colleague Joachim Goes and his team have to say about a particular instance: http://www.bigelow.org/climatechange/.
Speakerman...I think it's obvious that humans are affecting the climate in some way. You only have to look at the local "heat island" effect to see that. But it is also obvious that we cannot accurately predict what the effects of these changes will be. So I too get pretty nervous when I hear people spinning doomsday scenarios about the effects of global warming.
There may be more than meets the eye in that Heidke plot. Rather than just compute the average, why not fit, say, a cubic polynomial to thse data? I think it might show that there are times when forecasts do better than at other times, and we might ask ourselves what the reasons might be. It looks like they fared better in 1997-2000 than recently, to me.
speakerman -
total agreement here. i've argued this point on an individual basis and in letters to editors in local papers in response to alarmist global warming articles. i've come to the unpleasant conclusion that people have short memories and long political agendas, and rational thought is out of fashion. (another phd here, but plasma physics, not weather related).
Hecker, there definitely appears to be an oscillation in that skill plot.

Here's a theory: perhaps when forecasts are doing well, the forecasters tend to stick with the model (or set of models) that is working well at the time. Then, as climate patterns shift, the forecasters stick with that model too long, resulting in negative skill. Eventually the forecasters figure it out, and start relying on a different model, and the skill goes back up again. And the cycle goes on and on.
Sorry, psychic Helane, but I don't see a record winter here in the Twin Cities; for one thing it probably would have started already. Cool weather and strong breezes (25mph, gusting higher) did show up however, beginning yesterday, and tonight'll be the first hard freeze. While there are still a few die-hards in short shirt sleeves, I had to bring out the lightest coat, until I get acclimated. I have my own scale, like the Cat scale, for winter coats:

Cat 1 "You're such a wimp." Fake coat (i.e, passes for a coat in other parts
of the country), although it looks real enough.
Good for chilly days.

Cat 2 "OK, so I need a coat." It got below freezing. You'll be sorry if you
get caught waiting for a bus without this, even
though most of the time you'll be wearing it open.

Cat 3 "Oooh, it's chilly." But...it's still above zero.

Cat 4 "Bring out the down." In the minus digits, and Weatherpeople are
overemphasizing the wind chill factor.

Cat 5 "It's finally winter." The winter festival...timed to coincide with the
ten days it never gets above -15. Alternate
between that and refusing to go out (after all,
it does hurt to breathe).

I don't want to see a record winter, but I'd be happy with more good cross-country ski days than we had last year.
Squeak...one time I was stranded at MSP by Northwest, and their excuse was maintenance issues because of extreme cold. I couldn't believe it...I mean, the airline is BASED IN THE TWIN CITIES. Shouldn't they be prepared? It was damn cold, got down to -18 that night I think.
Ah but they are (as much as any major airline can be)...the laws of physics probably didn't want to change just to humor the airline.

However I bet they wouldn't have those problems if they'd relocate to Kansas. Then they could blame delays like that as the side effects of heathen folks watching TeleTubbies. A school board there just redefined the term "science" so that "its not limited to the search for natural explanations of phenomena."
The real problem was (as usual) labor. They had other planes, of course, but no one to service them, move luggage from one plane to another, etc.

I'm going to encourage science teachers in kansas to start teaching that lightning is a result of Thor throwing bolts around. No need to limit ourselves to natural explanations. And who here has ever seen an "ion"?
That's because you probably paid $154 for your round-trip ticket.

Airlines should start charging what it actually costs to fly, then they wouldn't be going bankrupt.

No, wait...I'll leave being critial to you.
squeak, are you some bitter NWA employee or something?
by the way, last time i flew kc to msp it cost almost $800. happy?
Yeah, Accuweather is predicting normal temps and well below snowfall for Chicago.

The fun stat is the one that says of the 120 years of recorded temperatures in Chicago, only about 50 days had the "average" high and low. So if the average high/low was 66/37 for today, the long-term odds of that temperature being reached today is about .10%. I personally know of one date in the last 4-5 years that was completely, totally normal.

Just an interesting fact.
By the way, de-icing equipment stops working at about -10 to -15, I believe. YMMV.
It wasn't de-icing, it was a valve that was stuck by the cold. Other planes were taking off that night. The air temp was colder when we took off at 7 the next morning than it had been at 8 pm the night before.
Maybe they should have asked you to blow on the valve to warm it up.
squeak, what exactly is your problem anyway? did i attack you personally?
Please applaud rwdobson for providing this afternoon's entertainment. He really needs it, because life is a real struggle for him.
Squeak, I see how you got your name, you insignificant little mouse. I won't respond to you any more, but I'd be happy to talk with any humans out there.
Geeees... I didn't see that coming...
21, I didn't either. Apparently criticizing Northwest Airlines is verboten.
You are adults.. I'm going home for the day..

See everyone tomorrow!

Bye =)
lol, yeah I see that! Have a good night RW!! See ya tomorrow! =)
In an effort to increase the civility of this comment board, I would like to reignite an old argument from above that died out. The argument that global climate change is inherently unpredictable because forecasts have no skill beyond about 10 days is a red herring. Those are two very different sorts of predictions. Weather forecasting is an initial-condition problem, i.e., the quality and completeness of the data used dictates the success of the prediction. However, our picture of the atmosphere is nowhere near that detailed, so chaotic effects from slight discrepancies between model input and actual conditions result in unpredictability very quickly. If we knew every atmospheric condition at 1-meter intervals throughout the entire atmosphere, within 30 days we would be unable to predict whether Baltimore would see rain or sunshine. Contrast this with the global warming forecasting, which is a boundary condition problem. Here we are examining the long-term trends in global temperature rather than the instantaneous, localized predictions of weather forecasts. In one case we are examining weather and in the other we are examining climate, and these are two very different problems. Thanks for the attention.

I have been lurking on this blog for a while, but am finally inspired to comment. Happy weather watching to you all!
Infinite: I would argue that your distinction between "weather" and "climate" predictions is, at some level, a distinction without difference. The seasonal predictions for temp and precip are more like "climate" predictions, not "weather" predictions, yet forecasters still have very limited skill in making these predictions.

Both are limited by lack of initial data, but more importantly, both are also limited by the chaotic nature of the processes that are being modeled.

Infinite: You make interesting points. One of the main points I was trying to make in a round about way is that the more you know, the more you become aware of what you don't know. Kinda of an ignorance is bliss take off.

You use three key words in your comments, "Long term Trends". That is also key point in my original comments. What is long term? The Maunder minimum lasted 60-70 years, depending on the criteria used to mark the beginning and end of that particular weather cycle. Hurricane cycles can be 30-40 years in duration. Ice ages and tropical periods and so on can persist for thousands of years.

I have been looking at sea surface anomaly temp data from the US Navy and other source for several years and can not find any consistant, long term patterns or differentials supporting sustained temp increases. I realize data averaging, detection methods, anlytical standards - algorithums and so on can distort the concluding data. Nothing is perfect.

If you take every thing all one way (in support of increasing temps) you are hard pressed to see even a 1 deg C average increase on the earths oceans during the past 50 years. The atmosphere, of coarse is far more volatile due to it being a significantly less dense media. Again, looking at the data you are hard pressed to see a 2 deg C increase and much of that,in my opinion is suspect. Satellite temp data for the last 30 years or so is so flat I wonder if the atmosphere could be that consistent.

At the risk of being overly metaphorical, true, unbiased long term evidence is thin and the jury is still out.

Caution and adherence to good science and data interpretation practices applied over a appropriate time period are absolutely essential before reasonalbe conclutsons can be made. As of now I personally do not think this criteria has been met.

I am seeing way too many folks sign on to the Global Warming theory with out having a clue as to what, if anything may be going on. As legend from the late 1920's goes, when the big money in the stock market starting getting unsolicited stock tips from elevator operators it was time to get out of the market.

Some things, particularly doom and gloom or something for nothing are easily over sold.


Dr. Masters, if you happen to see this post, I wonder if you might comment as to what reasons you see for your optimism that this year's hurricane season as "once-in-a-lifetime".

I'm feeling rather afraid that it might have been just a warm-up for what is to come. Is there any scientific reason to think this year was some kind of anomaly, given the accepted assumption that we are in for a trend of severe and frequent storms in the next couple of decades?

My goodness what a smorgasborg of conversation today. To those interested, I finally got a note back from Palmbeacher, shes back in Florida and ok.

LpAngel.... I sure hope the de-icing doesn't stop working at -10 to -15 or us in Alaska would be homebound till Spring. The airlines still fly even at -40 and -50 below. Its a little longer process, but we still fly. I always get nervous because at those temps you see Ice on the wings, but the guys and gals do an awesome, thorough job to keep the planes ready and able to fly without incident.

Global warming? Even since I have been here in Alaska, I've seen changes in the terrain up here. The Tundra isn't so barron anymore, there is actually growth of vegetation that normally isn't there and species of sealife found in waters way further north than usual. You should see what happens when Ice Fog takes over Fairbanks. Its nothing more than emmisions from exhaust being held down to the ground by the cold above it. Its painful to breath outside and you can literally move the fog with your hands. You cant drive without having your car IM'd in the winter up here and the fine is stiff. If what we see in this small place is an example of what effect global warming is having on the planet, I can only imagine what it would be like to combine it all across the planet. I shutter to think about what it would be like in a place like Los Angeles at 30 below zero. YUCK!
speakerman, you are persuasive in your arguments but I disagree with you. In the last 150 years there have been two major human induced disruptions to global climate:
- global warming from greenhouse gas emissions;
- global cooling due to the dust thrown up into the atmosphere from above ground nuclear testing

If you look at the surface temperature trends of the last 150 years you will see rising temps from the start of the industrial age through to the 1950s, a cooling trend lasting well into the 1970s, and a continuation of the warming trend since then. The cooling trend was due to the nuclear testing.

Take out that cooling effect from the bomb testing, and you have a steady rise in temps over 150 years with no end in sight. Our future climate will be very different from the one we grew up with, and many people are very concerned that it will be much less hospitable to human life.

Destiny...the temps at the higher altitudes where airliners fly, are much colder than on the ground, year-round. Any machinery that would be exposed to the outside air temp would have been designed to work even at fairly cold temps. On the ground before takeoff it is so important to avoid ice on the wings in order to make sure the plane has lift as it takes off. We see it a lot in MN during the winter so I guess they have designed the deicing equip to make sure it works even with low temps.

I remember one snowstorm I was on a plane where we had to go through the deicing more than once before takeoff. That was a little unnerving. Now, luckily, I don't have to travel every week.
Dear Jeff,

Are you noticing this odd little swirly low thing off the Pacific Coast west of Los Angeles? See

I've been watching this all day and it looks gradually better organized and somewhat stationary. Occasionally we do get whopper storms on the Pacific Coast here in the fall and winter (Inaugural Day Storm of 1992, another one on Nov 5 1982 and the 1962 Columbus Day Storm) - thus the interest in this thing.



insignificant little mouse? hmmmm... i should take exception to that, knowing what i do about mice, but i enjoy your intelligent comments too much to be bothered by an unintended slur...

with a wink and a nod,

Mousy, I realized too late that I may be slurring you with the mouse comment...but you seem to be a signifncant mouse that talks, and not squeaks...

not to worry... i don't take offense where none was meant

I'd believe that 30 years ago, forecasters didn't report the longer-term forecasts to the general public (if, for no other reason, because there weren't media dedicated to weather, and there's only so much time on the news). So it's possible that the weather reports of 30 years ago were more accurate than the weather reports of today, but less accurate than the corresponding portions of the more extensive weather reports of today.
The woolly worms here in Western North Carolina have ranged anywhere from solid black to black tips with a long brown stripe in the middle. So who knows... These things are all over the place during the late summer and early fall.