El Nino and East Coast Storms

The ongoing El Nino is apparently partially responsible for the low Hurricane count this past season. The El Nino pattern also generally results is an active winter storm pattern across the southern U.S. If you take that a step further, an El Nino year could enhance the chances for development of East Coast Winter Storms, often referred to as nor’easters, and the potential for significant snows in the Mid Atlantic region.

Jared Klein, a forecaster at the National Weather Service Office in Sterling, VA, addressed this possibility in a brief article he authored recently.


El Nino and Mid Atlantic Winter

Jared Klein
General Forecaster
National Weather Service

November 2009

The official National Oceanic and Atmospheric Administration (NOAA) Winter Outlook from the Climate Prediction Center (CPC) was released back in mid-October. The outlook favors below average temperatures and equal chances for above or below average precipitation in the greater Baltimore and Washington DC area for the upcoming 2009-2010 winter season (see figures below).  El Niño, which is a climate phenomenon characterized by unusually warm ocean temperatures in the tropical Pacific Ocean, is expected to play a key role in influencing this upcoming winter’s weather across the United States.

Looking back at past winters since 1950, approximately 17 were influenced by an El Niño episode. The figures below are composites of average December, January, and February (DJF) temperatures and precipitation, as well as seasonal snowfall at Washington, D.C. broken down by the strength of the El Niño episode. Both DJF temperatures and precipitation averaged near normal while seasonal snowfall averaged a few inches above normal. The strength of the warming in the equatorial Pacific Ocean (i.e. El Niño episode) shows a possible correlation to seasonal temperature, precipitation, and snowfall locally at Baltimore and Washington D.C.  Weak El Niño winters averaged below normal temperatures and precipitation, while strong El Niño episodes have resulted in above normal temperatures and precipitation. On average, the stronger the El Niño episode, the warmer and wetter the winters have been. These findings can largely  be linked to a stronger than normal sub-tropical jet that typically occurs during moderate to strong El Niño winters, which would favor more active storm systems from the south that draw warm, moist air northward as opposed to the drier Alberta clippers from the northwest. Seasonal snowfall averaged above normal for weak and moderate El Niño winters while below normal for strong El Niño episodes. During strong El Niño episodes, the bulk of the cold air remains north of the mid-Atlantic region, often resulting in precipitation falling as rain instead of changing to snow.

Not all El Niño winters are alike as many other shorter and longer term climate patterns influence the local weather. For example, although it might seem that all strong El Niño winters in Washington D.C. and Baltimore have been associated with above normal temperatures and precipitation and below normal snowfall; these atmospheric quantities have been variable each winter. Of the 17 El Niño winters, eight had above normal snow while nine were below normal.  The above average El Niño winters have been associated with some of our snowiest winters, especially during moderate El Niño episodes. With the ongoing El Niño episode expected to continue, even strengthen to moderate levels this winter, El Niño will likely play an important role with the winter climate here in the greater Baltimore and Washington D.C. area.


Our friends at “Earth Gauge” (National Environmental Education and Training Foundation) have put together a brief item that is tied to this and I pass it along to you.



December is East Coast Winter Storm (ECWS) season. These storms are powered by warm water that flows from the Gulf Stream. The Gulf Stream current flows along the Eastern Seaboard past Florida and the Carolinas before reaching Cape Hatteras, where the warm water heads out into the Atlantic. ECWS’s travel northward along the coast causing high winds and coastal property damage comparable to hurricanes. They also bring heavy snowfall, causing further weather complications. On average, there are 12 ECWS’s during the December to February season, with January being the most active month. One of the best predictors of how intense an ECWS season will be is the ocean temperature along the coast of the southeastern U.S. during the previous summer (Gulf of Mexico temperatures were above average this past summer). The warmer these waters are, the stronger the Gulf Stream generally is and the more active the winter storm season will be. Interestingly, conditions in the eastern tropical Pacific affect ECWS activity as well. What eastern tropical Pacific conditions are most conducive to an active ECWS season?

a)    El Niño conditions (warmer eastern tropical Pacific SSTs)
b)    La Niña conditions (cooler eastern tropical Pacific SSTs)
c)    Neutral Conditions (average eastern tropical Pacific SSTs)

The correct answer is a. More active ECWS seasons tend to coincide with El Niño years. This is in contrast to Atlantic hurricane season trends, as El Niño conditions tend to suppress Atlantic Hurricane formation. Over the second half of the 20th century, the frequency of ECWS events showed little trend, but the storms did become slightly more intense.

Sources: DeGaetana, AT et al. “Statistical Prediction of Seasonal East Coast Winter Storm Frequency.” Journal of Climate 15 (2002): 1101-1117 and Hirsch, ME et al. “An East Coast Winter Storm Climatology.” Journal of Climate 14 (2001): 882-899 and Eichler, T and Higgins W. “Climatology and ENSO-Related Variability of North American Extratropical Cyclone Activity.” Journal of Climate 19 (2006): 2076-2093 and National Oceanic and Atmospheric Administration: Climate Prediction Center. Accessed Online 7 December 2009 http://www.cpc.ncep.noaa.gov/products/precip/CWlink/stormtracks/eisdiffobs.meta.gif


A number of things have to come together to generate a nor’easter and to have that storm be a big snow maker for our area. The two items cited above are a couple of pieces of the puzzle that are apparently in place at the start of this winter season. Only time will tell if the puzzle will be completed

John Collins


2 Responses

  1. The weather is my passion, I have bookmarked this blog article so my weather freinds can enjoy it
    as much as me! Anything relating to the weather, news, photos really catches my attention.

    Oregon Scientific Wireless Weather Station

    Bristol Weather England

  2. Looks like much of the above was spot on for the 2009-2010 winter. 2nd April 2010.

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