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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....and talking about parts, there is a sign on the highway near here, advertising

"Used Japanese Body Parts"

I think it refers to Nissan and Toyota, doors and fenders and such, but I dare not stop to ask.
Member Since: October 24, 2005 Posts: 0 Comments: 24307
LOL Mom. How would you have explained that bag of parts to the Cops ??
Member Since: October 24, 2005 Posts: 0 Comments: 24307
Yes indeed. This season had some incredible moments.
The lonely damsel in distress with a hurricane approaching, trying to convince her stoned daddy to listen to reason.
Certain amazing revelations.
And storms that just would not follow instructions from the NHC or anyone.
Member Since: October 24, 2005 Posts: 0 Comments: 24307
We did once have a night of "carnage"... and lost 6 hens -- it was early on. We didn't sink the fence and a racoon dug under and ... I had to pick up chicken parts -- then my kid and I didn't know what to do w/the bag... so we're driving around at night with , God, chicken parts in a hefty bag ....
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it was fun..and we learned...and I made a few friends (you know who you are)..next year I will be a little more wiser and more tolerant.
Member Since: September 10, 2007 Posts: 0 Comments: 11149
Quoting pottery:
Only 2 chickens left, Mom ??
Heck no -- we have six plump ladies... we call them the girls!! They adore my son ... I'll never be w/out chickens again. We live in suburbia not rural -- so technically it's a no no.... but the neighbors are bribed w/fresh eggs... so it's all good
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Well,I am going to sign off for tonight.

Quikscat this morning did not show a surface low down near Panama but we know how quickly things can change. At 10 N the low may have been mostly onshore.

No pass for this evening downloaded as yet.

Hopefully this will fizzle out.
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I thought it was pretty funny (as ridiculous as it may sound) when stormkat came in with all these different handles thinking he was able to fool us into thinking it was a different person. Also, it was pretty laughable at times when JFV would ask if a tropical wave off of Africa would hit his house. Unsuprisingly, they both got banned. lol
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Dolly
-- my favorite wave maker of the season -- her waves were lovely -- Ike - hands down the dirtiest, nastiest waves of the season.. even came w/ the stinging jellies & sea nettles - nasty, nasty storm
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Only 2 chickens left, Mom ??
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823. pottery 1:54 AM GMT on November 24, 2008

LMAO !
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Same here with the mangos, my chickens would feast, gorge themselves on the ones I'd leave behind --I still have two left ..the very last two
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Quoting kmanislander:
822. Drakoen 1:53 AM GMT on November 24, 2008

LOL

We all had our moments but more importantly I would like to think we all had some fun.


Yes. It's all water under the bridge... until next year LOL!
Member Since: October 28, 2006 Posts: 57 Comments: 30486
822. Drakoen 1:53 AM GMT on November 24, 2008

LOL

We all had our moments but more importantly I would like to think we all had some fun.
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Quoting GeoffreyWPB:
LOL....there were some "unusual" times this season. We ought to come up with the top ten most outrageous or unusual posts that we remember. One of my most memorable was the person (forgot the name) who had to go to the hospital to visit his girlfriend who had been in a car wreck...but promised they would be back to post about a storm as soon as it was convienent.
b Tears are rolling down my face i'm laughing so hard -- that was a classic -- I mean it was like a comedy
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Hard luck on the mangos Kman. We had a MegaCrop. So much so, that one morning early I heard my wife making strange noises outside, only to see her being terrified by 4 or 5 enormous hogs that had escaped their coop, and were gorging on ripe mangos under one of the mangos in the garden. The dogs would have nothing to do with them.
The Muslim neighbour was boisterous in his reprimand, when they invaded his yard for his cherries........

edit, they were NOT my hogs....
Member Since: October 24, 2005 Posts: 0 Comments: 24307
Quoting kmanislander:
This was a very interesting season because we had so many systems that appeared to be at TD or TS status but were not. One thing I learned early in the season was not to pay too much attention to convective blow ups.

After Dolly, I started to be more analytical about convergence and divergence as well as looking at surrounding data. Drak nailed Dolly when many , including myself, thought it would be classified. It was, eventually LOL


Don't give me a yard I might take a mile LOL!
Member Since: October 28, 2006 Posts: 57 Comments: 30486
69 minutes to NHC update
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speaking of...as any one heard from storm w?
Member Since: September 10, 2007 Posts: 0 Comments: 11149
Quoting hurricanemaniac123:


Does that mean it's a td?
more like a hat trick
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This was a very interesting season because we had so many systems that appeared to be at TD or TS status but were not. One thing I learned early in the season was not to pay too much attention to convective blow ups.

After Dolly, I started to be more analytical about convergence and divergence as well as looking at surrounding data. Drak nailed Dolly when many , including myself, thought it would be classified. It was, eventually LOL
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Quoting GeoffreyWPB:
post what drak??? lol


Exactly. What are we talking about.
Member Since: October 28, 2006 Posts: 57 Comments: 30486
post what drak??? lol
Member Since: September 10, 2007 Posts: 0 Comments: 11149
I agree Drak...no one is perfect...but some of the bloggers were more adamant than others...to the point of being obnoxious...without looking at the reasoning of the other camp.
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784 mom
Yeah, but it just frustrates me that we don't see a more interdiscliplinary approach to planning a future.
Dollars spent on parallel universes, life in other galaxies and such. Seems to me that diverting those dollars toward basic neccesities in the not too distant future would be wise.
Member Since: September 11, 2008 Posts: 9 Comments: 10084
Personally, from my obs. of the trees and the leaf fall from some of them already, I am expecting an early start to the dry season here this year...
Also, the temps have already begun to drop, and the overall humidity as well. I was on the north coast today, and brisk winds from the N/E .
Dry season conditions. (but there were showers)
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See what happens if I leave for a minute? Something pops up for a Thanksgiving surprise.
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Quoting GeoffreyWPB:
I was thinking of StormW and I think CCHS


Then you can just forget post #805 ;P
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Quoting GeoffreyWPB:
it would be fun as a retrospective to go back to the archives and dig up and relive some posts from this season and see who had it right and who was very, very wrong. Coming to mind was Ike...with many respected posters refusing to believe it would cross Cuba.


Not to sound self-important, but... I thought Ike was going to hit TX the whole time... but not that it was going be in the Caribbean at one point though.
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I was thinking of StormW and I think CCHS
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Looks like were on Rene Alert.
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Quoting KEEPEROFTHEGATE:
T.C.F.A.
TD/18L/R
EST.POS.
80.1W/11.2N
MOVEMENT W
NEARLY STATIONARY


Does that mean it's a td?
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Quoting GeoffreyWPB:
it would be fun as a retrospective to go back to the archives and dig up and relive some posts from this season and see who had it right and who was very, very wrong. Coming to mind was Ike...with many respected posters refusing to believe it would cross Cuba.


some of the posts were deleted for this year... : (
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.
Member Since: October 28, 2006 Posts: 57 Comments: 30486
Quoting pottery:
Kman, dry from end Dec to june. But this year it rained right through to the first week of March. So last dryseason was short, but intense....


It seems like the seasons are mixed up of late. This year the dry season here lasted all the way to June. So much so that I only got 3 mangos from my Valencia tree !
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it would be fun as a retrospective to go back to the archives and dig up and relive some posts from this season and see who had it right and who was very, very wrong. Coming to mind was Ike...with many respected posters refusing to believe it would cross Cuba.
Member Since: September 10, 2007 Posts: 0 Comments: 11149
T.C.F.A.
TD/18L/R
EST.POS.
80.1W/11.2N
MOVEMENT W
NEARLY STATIONARY
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23/2345 UTC 10.5N 78.7W T1.0/1.0 INVEST -- Atlantic
Member Since: October 28, 2006 Posts: 57 Comments: 30486
Kman, dry from end Dec to june. But this year it rained right through to the first week of March. So last dryseason was short, but intense....
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Quoting kmanislander:
792. Drakoen 1:33 AM GMT on November 24, 2008

The HWRF has the inland motion over Costa Rica. That would suit me fine. Inland there would be a rain event only.


Yea. It's relying on northwesterly flow around a mid level ridge like the GFS as opposed to the GFDL who see a deep-layered trough being able to steering the system (being a hurricane).
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Hi Pottery,

I saw that you had some heavy rain down your way last week. When is your dry season ?
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post 789. LOL Mom. But some of us "ole times Regulars" have not exhausted themselves as yet. Nervous breakdowns and all.
heheheheh
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792. Drakoen 1:33 AM GMT on November 24, 2008

The HWRF has the inland motion over Costa Rica. That would suit me fine. Inland there would be a rain event only.
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Quoting GeoffreyWPB:
LOL....there were some "unusual" times this season. We ought to come up with the top ten most outrageous or unusual posts that we remember. One of my most memorable was the person (forgot the name) who had to go to the hospital to visit his girlfriend who had been in a car wreck...but promised they would be back to post about a storm as soon as it was convienent.


I think the most dramatic moments were during and then (even more so) after Dolly. Full-fledged war managed to spread into two blogs.
Member Since: October 28, 2006 Posts: 57 Comments: 30486
Quoting surfmom:
i can't believe I'm reading these posts and entertaining the idea of another 'cane...in November, when I'm freezing my butt off


It has even been " chilly " here, in a relative sense

73 in the morning with 30 knot winds is COLD for us LOL
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Wow, we went from "season's over" to "Rene might be here by monday".

Hello TS Rene. :-)
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Quoting kmanislander:
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.


The GFDL looks to be over doing things and always gets too over ambitious with it's initial runs. I'll stay conservative and go with the other models that take it into Panama as possibly a tropical storm. The GFS shows shear slackening somewhat; though, that is 4-5 days from now when it may already be going inland as shown by the BAM and GFS.
Member Since: October 28, 2006 Posts: 57 Comments: 30486
LOL....there were some "unusual" times this season. We ought to come up with the top ten most outrageous or unusual posts that we remember. One of my most memorable was the person (forgot the name) who had to go to the hospital to visit his girlfriend who had been in a car wreck...but promised they would be back to post about a storm as soon as it was convienent.
Member Since: September 10, 2007 Posts: 0 Comments: 11149
i can't believe I'm reading these posts and entertaining the idea of another 'cane...in November, when I'm freezing my butt off
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Quoting Drakoen:


I don't think we want "old times" with the regulars lol. This year was pretty bad with the drama.
Happily, most of them have "exhausted" themselves... Ike caused a lot of "nervous breakdowns"
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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???
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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.

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