Network News

X My Profile
View More Activity
The new Washington
Post Weather website
Jump to CWG's
Latest Full Forecast
Outside now? Radar, temps
and more: Weather Wall
Follow us on Twitter (@capitalweather) and become a fan on Facebook
Posted at 12:30 PM ET, 11/ 3/2010

The winter of 2009-2010: Could it have been colder?

By Jason Samenow

Global warming may have tamed fierce winter

* Thursday rain threat: Full Forecast through weekend *
* Why was it so snowy? El Nino and the North Atlantic Oscillation *
* Tomorrow: Capital Weather Gang's 2010-2011 winter outlook *

By Joe Casola, Special to Capital Weather Gang

This is the latest in a series of feature articles revisiting the historic winter of 2009-2010 leading up to Thursday's release of the 2010-2011 winter outlook.

The statewide climate division rankings show that it was quite cold across the Southeast this winter, relative to the 115 year record. For Virginia, this winter ranked as the coldest in the last 30 years; for Maryland, this winter was the 5th coldest in the last 30 years. Note: D.C. doesn't have its own NCDC climate division. Source: NOAA's National Climatic Data Center.

The 2009-2010 winter in the DC metro area, and more generally the Southeast, was cold. To accompany our record-breaking snowfall, we experienced a relatively chilly winter, a rarity during the last few decades. However, some recent research suggests that our region, and the Northern Hemisphere as a whole, was actually "lucky" - it could have been substantially colder.

Previous CWG posts have shown that our frigid and snowy winter was produced by some relatively large and persistent wiggles in the atmospheric circulation. During most of the winter, the air that normally resides over the polar regions across the Northern Hemisphere migrated equatorward, invading our mild latitudes. The configuration of ridges and troughs that permitted this flow was largely a product of a strong El Niño and the negative phase of the Arctic Oscillation.

To complement the cold air, the jet stream and storm track were displaced to the south of their normal locations, improving the chances that impending storms could follow an ideal "snow track," and approach from our south/southeast where they can benefit from the Gulf Stream's moisture. While not a guarantee for cold and snow, the occurrence of an El Niño or the negative phase of the Arctic Oscillation can help tilt the odds to a colder or snowier winter. In our case, we experienced a "double-whammy."

Huug van den Dool of the National Weather Service's Climate Prediction Center has used a statistical technique called "constructed analogs" to examine similar occurrences of such a "double-whammy" circulation over the period 1961-1990.

Northern Hemisphere mean and anomalous 500-hPa geopotential height. Mean heights are denoted by solid contours; red indicates anomalously high heights and blue indicates anomalously low heights. Northwesterly flow into the US Southeast supplied us with plenty of cold air. The pattern shown for January is similar to the entire December-February winter period. Source: Climate Prediction Center, NWS/NOAA

Analogs of this circulation are generated by applying a statistical algorithm to historical records of the upper-level atmospheric flow (specifically, the 500-hPa stream function). Interestingly, comparison of the observed 2009-2010 winter to the analogs that have been constructed from the earlier period show a significant difference in temperature for our region and across much of the Northern Hemisphere.

In other words, if the atmospheric circulation that occurred during this past winter had occurred sometime during the 1960s-1990s, then it would have actually been colder by roughly 1°C-2°C (1.8°F-3.6°F).

When averaged for the Northern Hemisphere, this result was also true for the other winters between 1991 and 2010 - the observed winter conditions of the recent two decades were warmer than the analogs constructed from the 1961-1990 historical data by an average of 0.5°C (0.9°F).

So why were we "spared" from a colder winter?

By itself, the constructed analogs technique does not necessarily point to a particular reason or mechanism as to why the 2009-2010 winter was warmer than the analogs drawn from the historical data.

It's possible that our "luck" during the recent winter resulted from some combination of global warming and the long-term, decade-to-decade variability in the Atlantic Ocean. Although it can be difficult to tease apart these factors (and such work is an active area of research), this analysis provides evidence of some important differences between the winters of today and those occurring during the mid-20th century.

Joe Casola works as a consultant, helping natural resource managers use weather and climate information as part of their decision-making process. He holds a B.S. in Chemistry from Duke University. After discovering he was a klutz when mixing chemicals in the lab, Joe decided to follow his passion for looking at clouds and earned a PhD in Atmospheric Sciences from the University of Washington. He has also worked on weather and climate issues at the National Research Council.

By Jason Samenow  | November 3, 2010; 12:30 PM ET
Categories:  Climate Change, Winter Storms  
Save & Share:  Send E-mail   Facebook   Twitter   Digg   Yahoo Buzz   StumbleUpon   Technorati   Google Buzz   Previous: Winter 2009-2010 mid-Atlantic snowfall map
Next: PM Update: Clouds for now, rain comes later


Two facts about last winter stand out:

First, although we got plenty of snow, I cannot recall any really sharp cold waves after the snowstorms...contrasting dramatically with some winters during the 1980's the brutal cold waves of the second Reagan inaugural [1985] and the period following the Air Florida crash stand out in my memory. In fact last winter, we had a remarkably dry January in between the December snowstorm [Snowpocalypse] and the February snowstorms [Snowmageddon]. This is one reason why the much-unneeded-rain crowd kept bedeviling me even though much of the snow melted slowly, and there was little snowmelt-related flooding; it was basically dry when no snow was falling. By contrast, during 1996, a winter also marked by abundabt snowfall and not much really cold weather, there was a major Potomac flood two weeks after the big January snowstorm.

Secondly, while our area was generally colder than normal during winter 2009/2010 much of the globe, excepting one region of north-central or northwest Siberia, was actually WARMER than normal [despite the comments of Mr. Q and other global-warming skeptics that last winter "disproved" global warming]. One hallmark of an El Nino winter is generally warmer drier conditions globally.

BTW this coming winter we may be in for some pretty sharp cold snaps with or without snowfall. The eruption of Mt. Merapi in Indonesia might add its cooling impact to the ongoing La Nina.

Posted by: Bombo47jea | November 3, 2010 1:22 PM | Report abuse

Good to see your work on CWG, Joe! Solid job of reporting on the different factors that may have contributed to last winter's temps and general atmospheric circulation.

Posted by: afreedma | November 3, 2010 2:50 PM | Report abuse

I have a question. On some of the weather sites I've been looking at, some people are saying that there have been an unusually greater number of coastal storms in the past month or so than expected for the La Niña right now. They said that this anomaly could be a factor this winter in terms of snow amounts. Does this hold true and will our area be affected in any way? Thanks!

Also, the winter of 95-96 occurred during a La Niña. Yet, the D.C. area received over 100% of its average seasonal snowfall, with some areas getting over 200% of their normal amounts. How did that happen?

Some of the seasonal forecasts for this winter have 95-96 as one of the analog years for this winter. Are they right?

Thank you!

Posted by: Yellowboy | November 3, 2010 3:16 PM | Report abuse


Those are all good questions to ask when we put out our winter outlook tomorrow...

Posted by: Jason-CapitalWeatherGang | November 3, 2010 3:23 PM | Report abuse

Thank you Mr. Samenow! I'm really looking forward to the winter outlook tomorrow!

Posted by: Yellowboy | November 3, 2010 3:49 PM | Report abuse

Really cold winters don't necessarily produce a lot of snow around here. 1976-77 was historically cold, but there wasn't much snow. 1993-94 was also very cold but our most memorable winter storms were sleet events.

1969-70 and 1978-79 were among the rare winters when snow and cold converged.

And last winter was great! The weather gods gave us all that great snow, but not severe frostbite.

Posted by: JerryFloyd1 | November 3, 2010 4:15 PM | Report abuse

Ok, several years of watching with no comments, now 2 comments in 2 days.

I can guess, from the articles you've been posting, where the winter prediction is going. On the one hand, a strong La Nina, which generally means warmer winters. On the other, the possibility of a strong NAO impact (was it on this site or elsewhere I read about a correlation between arctic melt and NAO?). Add to that the unpredictability, but globally upward trend, of climate change.

All told, what you seem to trend towards is some big swings, some lower lows than last year, particularly early on, but also many higher highs, and either way, much more chance of ice and sleet.

I could be completely misreading this - and I love the teasers you've been putting out, which are helping me understand the complexity of long range forecasting much more than Joe Bastardi does... I guess all I'm trying to say is that I'm really looking forward to tomorrow's winter outlook - and that I'm really grateful for, if not the actual skill, then at least the feeling of insightfulness, that this blog has given me.

And all that said - please say it's going to snow lots!

Posted by: josh28 | November 3, 2010 8:36 PM | Report abuse


I'd say that's some pretty astute reading of our content.

Posted by: Jason-CapitalWeatherGang | November 3, 2010 9:10 PM | Report abuse

Last winter was not particularly cold. My metric is whether the river freezes, not the sluggish Potomac at DC full of snow, but the Shenandoah with rapids. My experience is limited by having moved here in 2006, but last winter was the first unfrozen winter.

Whether the study included enough factors so that global warming is the only one left is debatable, but it is basically true that CO2 warming is more likely to warm a cold dry winter air mass than a humid )summer) air mass. So I am basically comfortable 'blaming" a less severely cold winter on global warming.

An aside, the fig tree by the house has survived the freeze and the rest are drooping, so now I know where to plant more...

Posted by: eric654 | November 3, 2010 9:17 PM | Report abuse

This is rich. We have a cold snowy winter (evidence of the global cooling the political/scientific frauds of the 1970s tried to sell us?), and the koolaid drinkers try to spin it as though it would have been colder but not for, you guessed it, global warming!!

Bottoms up, koolaid drinkers.

Posted by: koggly | November 4, 2010 11:15 AM | Report abuse

To me, this article is a reasonable use of constructive analogs. Constructive analogs are used operationally in seasonal forecasts based on past experience that they possess significant skill.

There were some scientists in the 1970s who thought global cooling was a serious possibility, but far far fewer than those including myself who now regard global warming as reality. I do not recall any evidence of fraud (deliberate falsehood) on the part of those who supported the idea of global cooling.

Posted by: Dadmeister | November 4, 2010 12:17 PM | Report abuse

KOGGLY this is suppose to be a place for science . It is not a place for the minldess blatherings of the Joe Bastardi --the Glenn Beck of the weather world -- and his Kook fox news henchmen to post this crap.

The 1970s -- now almost 40 years ago perception of cooling was wrong. That happens in science. This seems to be news to kooks like you.

One super warm winter does not prove GW.
One super cold winter does not disprove GW.

sorry. This is not a straight line. Its complex.

Posted by: wxrisk | November 4, 2010 3:48 PM | Report abuse

The comments to this entry are closed.

RSS Feed
Subscribe to The Post

© 2012 The Washington Post Company