Tim’s 2012 – 2013 DC Winter Outlook

For my 2013-2014 winter forecast please click HERE

In comparing the current sea surface temperature (SST) anomalies from a year ago, the Equatorial Pacific has warmed from last year’s La Nina pattern into a very weak El Nino.

        La Nina conditions in the Equatorial Pacific – October 2011
Very weak El Nino conditions in the Equatorial Pacific – October 2012

 

Why do meteorologists and climatologists care so much about sea surface temperatures when forecasting the upcoming Winter conditions?  Oceans cover 71% of the Earth’s surface and play a significant role in climate and weather. 

Water warms and cools more slowly than the continents and directly impacts the behavior of the westerlies (jet stream).   A driving factor for the back to back La Nina winters of 2010 and 2011 was the cool phase of the Pacific Decadal Oscillation (PDO).

The last time the United States was covered by such widespread drought was from 1954 to 1956. The New York Times published a fascinatingDrought’s Footprintatlas mapping drought conditions in the United States from 1896 to 2012.  Researchers have continued to study the connection between drought conditions and ocean oscillations in the Pacific (PDO) and Atlantic (AMO).

 

Image Courtesy: http://www.intellicast.com/Community/Content.aspx?ref=rss&a=151
  • The very latest forecast models just released predict that the current weak El Nino conditions will weaken further , possibly into ENSO neutral conditions (Neither El Nino or La Nina) as we head into the upcoming winter season.  I personally believe that until the cold phase of the PDO weakens a moderate to strong El Nino is not very likely.
http://iri.columbia.edu/climate/ENSO/currentinfo/SST_table.html
  • The strength of El Nino is significant because most of the forecasts that were issued during the late summer were using analogs (historical weather records) during moderate and in some cases strong El Nino yearsStronger El Nino winters typically feature mild conditions across the northern tier as well as a very strong, dominant, sub-tropical jet stream.  Now that the strength of the El Nino has weakened substantially you can practically throw out some of the analog years that were used in some of these premature forecasts.
Temperature anomalies across the United States typically experienced during a strong El Nino Winter (December through February).

 

The recent moderate El Nino winters of 2002 and 2009 produced several of Washington’s most memorable winters in recent history with the President’s Day Snow Storm of February 2003 and of course the December 2009 and February 2010 snow storms during the winter of 2009-10.  Storms carried by the sub-tropical jet stream along with high latitude blocking and arctic air produced perfect conditions for the high snowfall totals during those moderate El Nino wintersWithout the blocking and arctic air, those winters would have produced a lot of rain.  The graph below paints this picture well:  El Nino winters typically produce more moisture in the National Capital Region but not necessarily delivered in the form of snow.

 

DCstorms.com – Seasonal Snowfall at Washington National Airport (DCA) during El Nino winters

The images below clearly show the correlation between different phases of the  North Atlantic Oscillation (NAO) and Arctic Oscillation (AO) and winter weather across the United States.

 

Temperature anomalies in the United States associated with positive and negative phases of the NAO and AO during La Nina, La Nada (neutral), and El Nino winters.  Image Courtesy: Climate Prediction Center (CPC)

 

The Arctic Oscillation and North Atlantic Oscillation can not be accurately predicted more than about 2 weeks in advance. I expect a split jet stream this winter with both an active northern and subtropical jet stream.  If the current very weak El Nino can hold or strengthen, then the sub-tropical jet stream may dominate more this winterIf the sea surface temperatures weaken rapidly, then I suspect the northern branch of the jet stream will dominate more (especially during the second half of winter).

 

A progressive pattern may be more dominant during the upcoming winter if the NAO index remains in a neutral to positive phase as storms fed by a sub-tropical branch head out to sea versus up the coast.
The NAO index has been negative during a large portion of Summer 2012. If this trend continues through the Fall and Winter, then the probability of a blockbuster east coast storm increases due to high latitude blocking over Greenland and phasing of the northern and sub-tropical branches.

 

Factors I used when choosing my analogs: 

  • Winters characterized by a cool/cold PDO & weak/neutral El Nino conditions

 

  • The winters in the early to mid 1950s featured previous summers with severe droughts

 

  • The weak El Nino winters of 1976-77 & 1977-78 followed a parade of La Nina years

 

 

In the Mid-Atlantic states, I expect equal chances of temperatures to be cooler than normal or near normal
In the Mid-Atlantic I expect equal chances of normal or above normal precipitation.

I believe that last winter’s increase in solar activity (solar flare ups and storms) along with the positive AO and NAO caused much of the record warmth across the lower 48. Winter was held in Alaska last year.

 

  • I expect that the east coast will have several chances of coastal storms developing aided by the sub-tropical jet stream.  If the northern branch of the jet stream phases (comes together/unites) with the sub-tropical branch, and there is an adequate amount of cold air in place, several snow storms are likely. If the jet streams remain separate (lack of cold air and phasing) we will see some lighter mixed precipitation events and possibly even cold rain.

 

  • Based on the analogs I chose, there is an equal chance of above normal or normal precipitation in the Mid-Atlantic and New England.

 

  • There is an equal chance of  below normal or near normal temperatures this winter.

Based on the Analog Years I chose, here is what may fall at the Washington Area Airports this Winter:

Average Seasonal Snowfall in the Washington DC Region:

washington_dc_region_average_snowfall_dcstorms-com

Average Seasonal Snowfall in the Washington DC Metropolitan Area:

washington_metro_average_seasonal_snowfall_dcstorms-com

9 Replies to “Tim’s 2012 – 2013 DC Winter Outlook”

  1. Wow! What alot of work and cool looking maps; great job, Tim; get your masters in meteorology!

    On Sun, Oct 21, 2012 at 3:07 PM, DCstorms.com

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  2. Yeah, I am expecting ABOVE NORMAL snowfall, unlike last year for us in the mid Atlantic this year for this winter 2012-2013.

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  3. Hi Tim, Great work as usual ! It looks like we have a pretty good chance for a snowy winter here in Gaithersburg MD, if the NAO goes and stays negative for awhile. Do you see a chance for the same type of monster snowstorms for our area that occured in 2009 -2010 ?

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    1. The moderate to stong El Nino of winter 2009-2010 produced a persistent subtropical jet stream. This subtropical jet stream along with the negative NAO and AO gave DC a perfect storm track with an ample moisture to work with. This winter is featuring neautral conditions (neither El Nino or La Nina) in the Equatorial Pacific so it is looking like the southern branch won’t be as active as it was in 2009-2010. That being said, while this winter will not be a repeat of 2009-2010, we certainly could have a powerhouse Nor’easter move up the coast that could drop our entire ‘average snowfall’ with one storm.

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