Winter forecast, part II: NOAA's predicts a warm winter for the Central U.S.

By: Dr. Jeff Masters , 2:51 PM GMT on November 21, 2008

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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.

The official National Oceanic and Atmospheric Administration (NOAA) 90-day forecast for the upcoming winter, issued on November 20 by their Climate Prediction Center (CPC), calls for above average temperatures across the Central U.S. and Alaska. The remainder of the country has equal chances of above or below average temperatures. A dryer than average winter is expected over much of the Southern U.S., including the drought-stricken Southeast U.S.


Figure 1. Temperature forecast for the upcoming winter--December, January, and February 2009--made by NOAA's Climate Prediction Center. No areas of the country ar forecast to have an above-average chance of being colder than normal, but the Central U.S. has up to a 50% chance of having above-average temperatures.

How are the NOAA winter forecasts made?
NOAA uses several tools to make their forecasts. One key tool is their Climate Forecast System (CFS) model. This model includes a version of the GFS forecast model that we use for everyday weather and hurricane track forecasts. The CFS model also includes an ocean model that interacts with the atmospheric model. These models solve mathematical equations of fluid flow using a supercomputer for the entire globe, on a 100-km grid. NOAA also uses statistical models, which look at past winters and see how they depended on quantities such as sea surface temperature anomalies. Temperature trends are important, too--if it has been warmer than average the last ten years, it's a good idea to forecast a warmer than average winter.


Figure 2. Skill of the official 90-day forecasts issued 0.5 months in advance by NOAA's Climate Prediction Center. Note that the average skill over the past ten years is not very high (9 on a scale of 0 to 100), and has remained flat, indicating that our skill in making long-range forecasts has not improved.

How good are the NOAA winter forecasts?
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 90-day temperature forecasts issued 0.5 months in advance, NOAA has averaged a 9 out of 100 on the Heidke scale since 1995 (Figure 2). So, while there is some skill in forecasting what winter temperatures will be like, this skill is not much better than flipping a coin. Depressingly, Heidke skill scores for three-month precipitation forecasts are even worse, averaging just a one on a scale of 1 to 100 over the past 15 years.

Let's look at some examples. Last's year's winter temperature forecast issued in mid-November did poorly (Figure 3), failing to forecast that the U.S. would have equal areas with both above and below average temperatures. The 90-day forecast done in mid-November of 2005 for the winter of 2005-2006 was awesome, with a Heidke skill score of 45. However, the 90-day forecast done in mid-November of 2006 for the winter of 2006-2007 had virtually no skill, with a Heidke skill score of one.



Figure 3. Temperature forecast for Dec 2007-Feb 2008 issued by NOAA's Climate Prediction Center on November 15, 2007 (top). They predicted Equal Chances (EC) of either above or below-average temperatures for the Northwestern U.S. (white colored areas), and a 30-60% chance of above average temperatures over most of the remainder of the country. In reality, the U.S. experienced an average winter, with approximately equal areas of the country receiving above and below average temperatures (bottom). Image credit: National Climatic Data Center.

Why do seasonal forecasts do so poorly? Primarily, it's because the long-term weather patterns are chaotic and fundamentally unpredictable. To a lesser degree, we are limited by our imperfect physical understanding of what controls the climate, and our imperfect computer models we use to simulate the climate. As computer power continues to increase and our models include better representations of the weather and climate at finer grid sizes, I anticipate that seasonal forecasts will improve. However, given that long-range forecasts have not improved since 1995 despite a large increase in computer power, I doubt that this improvement will be more than 10-20% over the next thirty years.

Seasonal forecast models vs. climate models
A common complaint one hears about global warming predictions made by climate models is, "How can we trust the predictions of these climate modes, when they so such a lousy job with seasonal forecasts?" It's a good question, and there is no doubt that seasonal forecasts have pretty marginal skill. However, there is a fundamental difference between making a seasonal forecast and making a 100-year climate forecast. A seasonal or a short-term weather forecast is what mathematicians call an "initial value" problem. One starts with a set of initial meteorological and oceanographic values that specify the initial state of the planet's weather, then solve the equations of fluid flow to arrive at the state of the atmosphere a few days, weeks, or months into the future. This forecast is highly sensitive to any imperfections one has in the initial conditions. Since there are large regions of the atmosphere and ocean we don't sample, it's guaranteed that the prediction will suffer significantly from imperfect initial conditions. Furthermore, the chaotic and turbulent nature of the atmosphere leads to many "bumps" in the weather pattern over time scales of days, weeks, and months. The nature of turbulence makes it impossible to accurately forecast these "bumps" that are superimposed on the mean state of the climate.

A 100-year climate forecast, on the other hand, is what mathematicians call a "boundary value" problem. Given an initial and final set of factors (called "forcings") that influence the climate, one runs a climate model 100 years into the future. The final state of the climate will depend on the strength of the forcings supplied. This type of model is not very sensitive to initial conditions, and is not trying to forecast the "bumps" of chaotic, turbulent atmospheric motion superimposed on the mean climate. Rather, one is trying to forecast the mean climate. As computer power increases and our physical understanding of how the climate works grows, these type of models will continue to significantly improve. While climate models do fail to properly simulate important aspects of our past climate, such as the Arctic warming of the 1930s, and the observed 0.1°C global temperature increase that occurs at the peak of the 11-year solar sunspot cycle, they have been very successful at simulating things like the global cooling triggered by the 1992 Mt. Pinatubo eruption, and the observed pattern of greatest global warming in the Arctic. I believe that climate models are already significantly more reliable than seasonal forecast models, and should continue to improve steadily in coming years.

Support the Portlight Christmas for Gulf Coast Kids Honor Walk
Saturday is the portlight.org Christmas for Gulf Coast Kids Honor Walk. This is a fundraiser to buy gifts for the kids along the Gulf Coast who might not have much in their stockings this year because of the ravages of Hurricane Ike. Our own StormJunkie will be walking up the Arthur Ravenel Jr. Bridge in Charleston, SC, and will be taking his webcam along. Tune in to the webcam site at 2:30 pm EST to follow the walk, and participate in a live chat. Sponsorships of any amount, small or large, are appreciated! The cam will go active about an hour before the walk. It should be a cold but beautiful day.

Jeff Masters

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It could form, go south, cross panama and become a hurricane in the E. Pacific and become Rene (with accent)- Rachel???
Member Since: October 15, 2008 Posts: 11 Comments: 2305
We definitely do not need even the rain from it as numerous homes and other buildings in Cayman Brac and Little Cayman are still trying to do roof repairs from Paloma. In fact, in Cayman Brac many homes lost the entire roof and any rain now will do further damage to the interiors.
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Quoting hurristat:

this is called the NO rule. Anything after the letter N is hard to predict.
and not much of anything was easy to call this year -- all the rules were broken
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781. Drakoen 1:26 AM GMT on November 24, 2008

The gfdl run has it essentailly sitting there all week. By next weekend it is still shown as being E of Nicaragua near 14N.

If that plays out the shear may have slackened by then but I have not had a chance to look at the long range shear forecast.
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Quoting pottery:
Sheph, post 766.
Correct. Except that there is no way we would farm those areas in a holistic way. We will deplete the soil there in quick time, and have to use chemical nutrient to keep the yeild up.

Agreed!
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Quoting GeoffreyWPB:
nice to see the regulars around for the last time this season...seems like old times!


I don't think we want "old times" with the regulars lol. This year was pretty bad with the drama.
Member Since: October 28, 2006 Posts: 57 Comments: 29886
Link
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Quoting kmanislander:
774. Drakoen 1:21 AM GMT on November 24, 2008

LOL, yes I have been lurking and hoping it was all over. The shear map says this thing should be torn apart but there it is persisting and looking better all the time.


The SHIPS initialization shows 20 knots of shear over it. It can't afford to move north. You can see on water vapor imagery the strong upper level winds spreading that moisture all the way back to the eastern Caribbean.
Member Since: October 28, 2006 Posts: 57 Comments: 29886
769 pot
Yeah, just toying with the idea.
I wonder if the coral reefs would migrate north?
Too many questions??? I'll stop. lol
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Quoting kmanislander:


Yep, November is the time of year when the crazy systems come out to play. Current steering would suggest W over land but typically anything down there heads due N then NE.

Boy, am I weary of this season.

this is called the NO rule. Anything after the letter N is hard to predict.
Member Since: October 15, 2008 Posts: 11 Comments: 2305
774. Drakoen 1:21 AM GMT on November 24, 2008

LOL, yes I have been lurking and hoping it was all over. The shear map says this thing should be torn apart but there it is persisting and looking better all the time.
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nice to see the regulars around for the last time this season...seems like old times!
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Last news I heard from Caracas, is that 4 people died as a result of heavy rains there on Friday.....Same cloudmass/wave that resulted in 2 deaths here, and major damage due to flooding and landslips on Tues and Wed last.
Member Since: October 24, 2005 Posts: 0 Comments: 24023
Quoting pottery:
Hi Kman. And that system has been sitting there, stationary, for over a week too. Weirdness........


Yep, November is the time of year when the crazy systems come out to play. Current steering would suggest W over land but typically anything down there heads due N then NE.

Boy, am I weary of this season.
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Quoting kmanislander:
Hi Everyone

Well, I never thought I would be back blogging about another invest in the SW Caribbean. The GFDL is very aggressive with it and develops a Cat 2 hurricane by next weekend.


Something tells me you have been lurking about...
Member Since: October 28, 2006 Posts: 57 Comments: 29886
Hi Kman. And that system has been sitting there, stationary, for over a week too. Weirdness........
Member Since: October 24, 2005 Posts: 0 Comments: 24023
10-4 pot
Sounds like a "Nobody knows you when you're down and out" weekend.
Pull out the six string and pour a rum brother.
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Hi Everyone

Well, I never thought I would be back blogging about another invest in the SW Caribbean. The GFDL is very aggressive with it and develops a Cat 2 hurricane by next weekend.
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Sheph, post 766.
Correct. Except that there is no way we would farm those areas in a holistic way. We will deplete the soil there in quick time, and have to use chemical nutrient to keep the yeild up.
Member Since: October 24, 2005 Posts: 0 Comments: 24023
Hi Sheph.
No fishing. Sat around doing nothing but overdoing. Feeling bloated right now. It was good. Weather was not co-operative for fishing......
Member Since: October 24, 2005 Posts: 0 Comments: 24023
767. JLPR
wow we have 96L and wow it looks good...
wow lol
It looks like here comes the R =P and I thought the season was over =S
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759 Stsim
Understand.
But your referring to current areas which require considerable amounts of modern fertilizers to produce on depleted soils.
The northern migration of crops into almost virgin agricultural regions would have a tremendous yield
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it should be inland within two days..and I am sure no HH will be sent down...The NHC will base it's strength soley on all the satellite, ship and land observations. Are there any radars in that area that can pick up this invest?
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Looks good on the AVN too...
Member Since: October 28, 2006 Posts: 57 Comments: 29886
96L looks good for not being a TD or TS it think we may have are R storm come monday or sooner if this keeps up

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Shouldn't we give invest numbers to the start of the "snow hurricanes" we're sure to get real soon. Numbers like -20L LOL.
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Quoting IKE:
18Z HWRF slams 96L into central-America as a tropical storm....Link


And relatively smaller lol.
Member Since: October 28, 2006 Posts: 57 Comments: 29886
758. IKE
18Z HWRF slams 96L into central-America as a tropical storm....Link
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757. IKE
18Z GFDL turns 96L into a cane...Link
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MichaelSTL
At what point during global warming will the growing seasons be extended in the northern climates where the soil is more fertile producing more food for the world's hungry?
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The GFDL makes 96L a hurricane eventually. Most likely over done.
Member Since: October 28, 2006 Posts: 57 Comments: 29886
Quoting IKE:


Yeah it does, doesn't it...lol.


and alaska's red... funny :)
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Member Since: October 28, 2006 Posts: 57 Comments: 29886
750. IKE
Quoting StSimonsIslandGAGuy:
Ike's maps sure have the USA a nice shade of Obama blue :)


Yeah it does, doesn't it...lol.
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We could get another system. Fat lady hasn't sung yet. Pretty decent area of convection in the southern Caribbean. Increasing 850mb vort max in the area and strong upper level diffluent flow aloft.
Member Since: October 28, 2006 Posts: 57 Comments: 29886
Also, send any and all responses to my WU mail.
Member Since: October 15, 2008 Posts: 11 Comments: 2305
hey, everyone, only enough time to post just this... I have a question for everyone. Does anyone know where to find data on the Tropical Depressions in the Atlantic prior to 1991 and in the Eastern Pacific prior to 1988?? I looked through all the reports when you go to past storms, and the range of dates, and I have looked through all those. Anything that ends in -prelim/ does not contain tropical depression data, and any years before there is just -prelim/ do not have adequate data. So if anyone else knows where to find data on these storms, it would be greatly appreciated.

Thanks
-hurristat
Member Since: October 15, 2008 Posts: 11 Comments: 2305
Hi Pot
Any wahoo stories?
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742. IKE
Quoting MichaelSTL:


LOL

I ought to just ignore you... that is regional cooling or better, "weather". What about the rest of the globe?



Some cold areas... some warm areas... overall? More warm than cold (at the same time the U.S. is expected to be cold, Canada is expected to fry), thus global warming (do you need a definition of global)?


And you can ignore me if you wish. I don't care.
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741. IKE
Quoting MichaelSTL:


LOL

I ought to just ignore you... that is regional cooling or better, "weather". What about the rest of the globe?



Some cold areas... some warm areas... overall? More warm than cold (at the same time the U.S. is expected to be cold, Canada is expected to fry), thus global warming (do you need a definition of global)?


I was joking....lighten up....please.
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as an addendum to my above post -- I do not ban, I do not ignore --- The only time I use those aids are for cruelty and troll behavior

It is good to be a crusader and question authority, but keeping tolerance & compassion is important
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Quoting surfmom:
I have not the scientific background, or savvy to discuss GW -- but I feel that until we do know for sure.... why would we do anything that could be contributing to a situation that is not healthy for the planet earth.
\
Why do you say that? It is not a matter of "until we know for sure", though a lot of deniers want you to believe otherwise.

Ok MichaelSTL -- You called me OUT, and I am glad you did...I tried to take a wuss position --cause I am not savvy enough to scientifically stand up for myself, and I was being a chicken rather then stand up for my beliefs with some of the big dogs.... but I will go on record and say YES I AGREE WITH YOU MICHAEL, and we do have a problem happening -- I don't know how much of it we the humans have caused -- we are certainly in the "witches brew", but
like the economy until it clearly effects our Bellies---most of us will not address the issue and believe what we are being spoon fed via the media.
Never teach a pig to sing, it only frustrates you and annoys the pig
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Leave it to MichaelSTL to threaten the "ignore" or "ban" when someone disagrees with AGW.

He banned me from his blog because of it. It's fine though. I have no room for those who are intolerant of critical thinking.
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Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.