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Posted at 10:00 AM ET, 11/ 5/2009

Capital Weather Gang 2009-10 Winter Outlook

By Matt Ross

Odds favor cold, snowy winter

* 5-Day Forecast | Hypothermia season underway | Photo contest *

After a string of lackluster winters, this one could deliver for cold/snow lovers. We are forecasting the coldest winter since 2003-04 and the snowiest winter since the epic winter of 2002-03 when 40-60 inches buried the region, unless El Niño (an event characterized by warmer-than-normal sea-surface temperatures over the equatorial Pacific that can lead to shifts in weather worldwide) has some tricks up its sleeves.

Already, this El Niño event has reached moderate levels. The biggest threat to our forecast is the possible development of a strong El Niño. Often, when an El Niño gets too strong, we get flooded with warm air resulting in mild air and rain rather than snow. We're giving this a 30% chance. On the other hand, if the El Niño weakens rather than strengthens, it would likely result in similar (or even deeper) cold to what we're expecting, but it would probably give us a bit less snow. There is a 10% chance of this possibility.

Overall, we find chances for a large snowstorm of 8"-12"+ are much higher than normal this coming winter. No two winters are alike, but we expect this winter to share some similarities with the winters of 1957-58 (Reagan National Airport snow: 40.4"), 1965-66 (28.4"), 1986-87 (31.1"), 1994-95 (10.1"), 2002-03 (40.4"), and 2006-07 (9.5").

Keep reading for the detailed outlook and methodology. And if you haven't already, join us on Facebook and follow us on Twitter.

While significant advances have been made in seasonal forecasting, there is still a great deal of uncertainty in developing these outlooks. This is a low-confidence forecast, especially the overall snowfall estimate, where one big storm (or the lackthereof) could make or break the forecast.

OUTLOOK DETAILS

Monthly and Seasonal Temperatures

Overall Temperatures for December through February:

1 to 2 degrees colder than average

Monthly temperatures relative to average

December: Average
January: 1 degree colder than average
February: 3 degrees colder than average

Note that monthly temperature predictions are less reliable than overall seasonal temperatures. A cold or warm pattern lingering a week too long or ending a week short can greatly alter a monthly mean.

Snowfall

Much of our seasonal snowfall could come in several large events. There will be plenty of periods with little or no snow as happens in even our snowiest winters.

Our snowfall projection covers November through April (current 30-year running averages in parentheses):

Overall: 150% to 175% of average

Reagan National Airport (DCA): 24" (14.2")
Dulles Airport (IAD): 31" (20.4")
BWI: 30" (18.0")
Fairfax/Loudoun/Montgomery counties: 26"-36"
Arlington/Alexandria/PG/DC counties: 22"-30"

METHODOLOGY

Below are the factors that we have deemed most important in determining conditions this upcoming winter. No single factor tells the whole story, nor are the correlations between current/past conditions and future conditions always strong. But we have chosen factors that in the past have proven to at least have some predictive value. And when considered collectively, they help paint a picture of what we believe is most likely to happen this winter.

Equatorial Pacific Ocean

After a 2 year La Niña event, we are currently in the midst of a rapidly strengthening El Niño. El Niño is an oceanic phenomenon in which sea surface temperatures along the equator from the coast of South America to just beyond the international dateline run unusually warm. Based on modeling, past El Niño events, and current evolution, we are forecasting the persistence of a moderate El Niño event through December that starts to weaken during January and into February. Since the Niño regions (where El Niño establishes itself) are thousands of miles long, where the most anomalously warm water sets up is important. We believe this will be a center/west based event.

Typically when the core anomalies set up in the center and western flanks of the Niño regions, the potential strength of the El Niño is capped in the moderate range. Some past winters with a similar strength and configuration were cold and snowy such as 2002-03 and 1986-87, while others had more mixed results such as 1994-95 and 2006-07.

North Pacific Ocean

The Pacific Decadal Oscillation (PDO) is a measurement of the intensity and location of sea surface temperature anomalies in the North Pacific. When it is strongly positive it often correlates with a cold and stormy pattern for the mid-Atlantic. When it is sharply negative, it is often, but not always, warm and dry. Measured monthly, it also oscillates in predominant cycles that can last 2-3 decades. From the late 1940s to mid-1970s we were in a predominantly negative PDO cycle, and from the mid-1970s to late 1990s a predominantly positive PDO cycle. Since then, it is unclear what phase of the PDO we are in, though there is some evidence we may be in a predominantly negative phase.

During La Niña events the PDO tends negative and during El Niño events it tends positive. After 2 years of sharply negative readings, the PDO flipped to its positive phase in August, September and through October. We expect the PDO to lean positive this winter (though not decidedly so) and perhaps act stronger than the index implies.

We are starting to see sea surface temperatures in the North Pacific take on a more favorable signature for a ridge in the West and trough (dip in the jet stream) in the East, conducive to cold air in our region. While not as impressive looking as 2002, which had a huge warm pool in the Gulf of Alaska, we should still expect a more stormy pattern than the last 2 winters, with an active subtropical jet stream.

The evolution of the PDO in 1957-58 serves a possible analog to what we may experience this year. It was somewhat positive overall, occurred after a La Nina period of negative readings, and ran counter to the predominant phase. It also acted stronger than the index indicated. We received 40" of snow that winter.

Summer/Fall Pattern

Just as this past winter was our first below normal temperature winter since 2003-04, this summer was our first below normal summer since 2004, even if a hot August tried to throw a wrench in that. The predominant theme this summer was a huge trough in the center of the country leading to much cooler than normal temperatures in the Great Plains and Upper Midwest. After a September that was warm in the Northern Plains and cool in the East, we have seen the predominant summer pattern repeat itself in October with the coldest anomalies setting up in the same places it did this summer. Good analogs for the overall summer pattern are 1965 and 1994. As we have gone through Fall, we have seen a pattern quite reminiscent of 2002 set up. It should also be noted that this October featured our 5th colder than average month in the last six, something we haven't seen since 2003.

Quasi-Biennial oscillation

The Quasi-Biennial Oscillation (QBO) is a measurement of stratospheric winds over the equator. It is currently in a strengthening negative/easterly phase. In the past this has been very favorable for high latitude blocking or upper level high pressure at northern latitudes. In particular, it correlates well with a Greenland Block or negative North Atlantic Oscillation (-NAO) which is typically favorable for a cold and stormy pattern in the mid-Atlantic.

Miscellaneous

Other factors that were considered, but carried less weight, include 2009 hurricane season, local and nationwide precipitation patterns of the summer and fall, significant events, and persistence (the idea that predominant patterns/phases can persist for months/years until something significant changes them).

Stay tuned throughout winter for updates and insights, as well as detailed coverage of every event.

RELATED LINKS

Winter weather hype here and in high gear
Last year's winter outlook
Last year's winter outlook live chat
Last year's winter outlook recap
2007-2008 winter outlook
2007-2008 winter outlook recap

(In addition to CWG's Matt Ross, the lead author, CWG's Jason Samenow, Matt Rogers, Dan Stillman, Andrew Freedman, Steve Tracton, Greg Postel, Camden Walker, and Josh Larson also contributed to this outlook.)

By Matt Ross  | November 5, 2009; 10:00 AM ET
Categories:  Capital Weather Gang  
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Comments

woohoo! i get 24" of snow! (still, always make me wish i lived "north and west of the city".) here's hoping el nino stays weakish.

Posted by: walter-in-fallschurch | November 5, 2009 10:08 AM | Report abuse

I am definitely in the mood for some MUCH NEEDED SNOW!

Posted by: joseph4 | November 5, 2009 10:23 AM | Report abuse

I'm just worried about that rapidly strengthening El Niño. Let's hope it stays close to where it is right now.

Posted by: hobbes9 | November 5, 2009 10:37 AM | Report abuse

Well done, Matt.

Posted by: NoVaSnow | November 5, 2009 10:47 AM | Report abuse

The most accurate prediction about DCs winter weather is that DC weather predictions are usually wrong.

Posted by: 123cartoon | November 5, 2009 11:03 AM | Report abuse

I'm trying to not get excited about this, because then it will just hurt that much more when it's yet another winter of cold rain.

Posted by: kallieh | November 5, 2009 11:06 AM | Report abuse

Pleeeeeeeeeeeeeeeeeease, please, please, please, please let it snow...pleeeeeeeeeeeeeeeeeeeeease... =D

and if you guys let me down, I'm throwing rocks at somebody's house winders... =[

Posted by: cbmuzik | November 5, 2009 11:13 AM | Report abuse

Fingers and toes crossed that El Nino doesn't weaken! I always say I'm not going to get my hopes up and I always do anyways. My unscientific gut is telling me the snow is coming :)

Posted by: Snowlover2 | November 5, 2009 11:25 AM | Report abuse

Nice summary. Around DC, a major snowstorm (MECS, 8-12+") can by itself get us at least 50% of our annual snowfall average, and one historic (HECS, 16+") storm can practically get us all the way there. MECS/HECSs don't usually happen in isolation however. (The 2006 MECS, which was historic in the NYC area and central MD, is one exception.) PD II was preceded (and followed) by several significant events, the big one in Jan 96 was followed by a couple of significant events just that week and by two MECSs in February. I can't recall the last time the DC area "nickel and dimed" its way to our seasonal averages: that is, arrived there without the benefit of at least one MECS but instead strung together a number of 2-6" storms.(1981-2 had several moderate snowfalls but I don't think any of them were in the general 8"+ range.) Then again, we rarely get to seasonal averages in snow around here without substantially exceeding that average. Most years, we're left watching Miller B's blow up off Cape May while we hope against hope we can squeeze an inch or two out.

Posted by: catatonia | November 5, 2009 12:52 PM | Report abuse

Snowlover2,
i think they're saying el nino is good where it is (moderate), but if it strengthens it's bad for snow.

the ominous part is,
"The biggest threat to our forecast is the possible development of a strong El Niño."

coupled with,

"After a 2 year La Niña event, we are currently in the midst of a rapidly strengthening El Niño."

yikes!

Posted by: walter-in-fallschurch | November 5, 2009 12:58 PM | Report abuse

catatonia, others?
speaking of historic storms and all, why don't we ever get multi-day storms here?

this past few weeks we've had stretches of pretty heavy rain for 3,4,5? days in a row. our snow storms here are generally a 6-12 hr. big (hopefully) dump of snow followed by a week of sun...

Posted by: walter-in-fallschurch | November 5, 2009 1:14 PM | Report abuse

No, you're right, Walter. Thank you for pointing that out! I did mean strengthen :)

Seems as with everything else, moderation is key. Whether we're talking pie or el nino.

Posted by: Snowlover2 | November 5, 2009 1:14 PM | Report abuse

LET IT SNOW!!! LET IT SNOW!!! LET IT SNOW!!!

When it snows, ain't it thrilling,
Though your nose gets a chilling
We'll frolic and play, the Eskimo way,
Walking in a winter wonderland.

Posted by: sigmagrrl | November 5, 2009 1:25 PM | Report abuse

This sounds most like Bombocast Option 3, which predicts an East Coast trough through much of the winter & a strengthening subtropical jet into January/February. Several episodes of much-needed snow are likely.

Still possible: Option 1, the repeat of the nasty but mild Nino winter of '97/'98.

One precaution: Be careful if there's lots of cold & snow/ice during December. Jan./Feb. could end up a mild "bust" though the cold might be back in March.

If this verifies, watch for one or two Metro shutdowns & a Fed shutdown or two.

Posted by: Bombo47jea | November 5, 2009 2:23 PM | Report abuse

@ catatonia:

WE need the Miller B's to "bomb" up off Myrtle Beach/Savannah, not off Cape May or Delmarva.

The strengthening offshore subtropical jet projected for Jan./Feb. 2010 should give us plenty of opportunities.

As for Miller A systems, too many of those seem to blow up in the Northern Gulf & track west of the Appalachians. We get rain. Rarely we can get a doozy of a Miller A which blows up near Panama City or Pensacola, then tracks across North Florida and up the Atlantic just offshore. Such was the track of the famed "Knickerbocker" storm.

Posted by: Bombo47jea | November 5, 2009 2:36 PM | Report abuse

Hope u guys r right, but I'm not as optimistic. I expect the El Nino 2 be stronger & last longer than expected, & the NAO to b slightly +, ergo I'm calling for temps 2 average +1.5 to +3.5 & snowfall 4-7". I also checked my predictions 4 the last 5 yrs & have been right all 5 yrs on temp & 3 times on snow.
04-05
Called 4 temps av. to +2 & 10-13" snow
Actual, temps +1, snow 11."
05-06
Called 4 temps +3 to +5 & 3-5" snow
Actual, temps +3.6, snow 13.5"
06-07
Called 4 temps +1 to +3 & snow 5-8"
Actual, temps +1.1, snow 5.9"
07-08
Called 4 temps +2 to +4 & snow less than 5"
Actual, temps +3.1, snow 3.6"
08-09
Called 4 temps -1 to +1 & 12-16" snow.
Actual, temps -.8 & snow 2".
Being a snow lover I will gladly eat crow if my forecast is wrong, but it always seems like the El Nino ends up stronger & last longer than 1st predicted, & NAO trends to +.
Confidence level 4 my prediction is low, as I think their's a fair chance that all the systems could line up just right,& produce a 20"+ snow total. So I'm praying 2 the snow gods that I'm wrong.

Posted by: VaTechBob | November 5, 2009 3:40 PM | Report abuse

Good write-up. Good luck with your call.

Posted by: CarolinaMike | November 5, 2009 5:23 PM | Report abuse

I think given the good start (an October snow in the Blue Ridge Mtns), the mid-Atlantic will have a decent snow year.

Posted by: spgass1 | November 5, 2009 5:43 PM | Report abuse

@ Bombo47 --

When was the last time a Miller B gave DC a great snowstorm? Think back over the past great snowstorms; PD I is the only one that could be definitely characterized as a Miller B. Most Miller B's are high and outside for our area: Feb 1978 and Dec 2000, for instance.

What we generally want in the DC area for a epic event is a double barreled system: the first low in the southern Apps that gives us a lot of overrunning precip, and that low weakens while a secondary low off the Carolina coast intensifies, and then moves on up. (This was the case in Feb 03 and Jan 96.) I've never been sure how the classification scheme considers these situations; they are not classical Miller A's, I suppose, which are lows forming in the Gulf of Mexico and moving up the coast (re: March 93 or the first of the back-to-back storms of Jan 87). But Jan 96 and Feb 03, the initial low didn't track into the Ohio Valley. I have read NWS papers that categorize Miller B systems where the secondary cyclogenesis occurs either south or north of Cape Hatteras. I suppose, then, that both PD 2 and the Blizzard of 96 could be considered quasi Miller B's, if you apply this categorization. I'm generally (if albeit totally nonscientifically and, given being a snowlover in DC, masochistically), inclined to say that Miller B's almost always screw us over.

Fundamentally, I just want a HECS, whether it's Miller A, B, C, or a Smith D-1 or a Wojohowitz A-568888.

Posted by: catatonia | November 5, 2009 9:01 PM | Report abuse

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