El Niño at Winter Time: the Set Up for the Perfect Winter Storm

By: Sharra Klug
By: Sharra Klug

The 2009-2010 winter season is already in the record books and we're only a few weeks into it.

The 2009-2010 winter season is already in the record books and we're only a few weeks into it.

Starting with our first snowfall in October, the 2009-2010 winter has proved to be active. Looking at the months ahead, we can only assume the trend will continue and here's why.

During any given time, we are in an El Niño phase, La Niña phase, or neutral phase. We entered an El Niño phase during the first half of 2009 as ocean temperatures in the tropical Pacific became anomalously warm. This El Niño Southern Oscillation is also known as ENSO.

ENSO plays an important role in the weather for the Valley and across the country throughout the year. Data has been recorded since the 1950s in the D.C. Metro Area concerning ENSO and its effects on our area. While El Niño seasons are associated with less active Atlantic hurricane seasons, we can expect more active winter seasons.

El Niño affects the position of the subtropical jet stream, a feature in the mid-levels of the atmosphere where storms typical develop. The warm waters of the equatorial Pacific feed more energy and moisture into the atmosphere. The additional moisture and warmth move along the subtropical jet into the Gulf of Mexico, allowing for more energized storms to travel through the Southeast and potentially up the Eastern Seaboard.

El Niño affects the Shenandoah Valley and the D.C. Metro Area in reference to temperature and precipitation. Some of our biggest winter storms occur during El Niño seasons because of the enhanced moisture and warmth.

There are different levels of El Niño: weak, moderate and strong. Based on data collected by the National Weather Service in Sterling, Virginia, the stronger the El Niño, the warmer and wetter our winters are during the months of December, January and February.

Weak El Niño phases are associated with below average temperatures and precipitation for the Valley. With the cooler air in place, we have better chances for snow events.

Moderate El Niño phases keep our temperatures and precipitation amounts near our seasonal averages. We have the best chances of seeing substantially above average snowfall seasons during moderate El Niño phases.

Strong El Niño phases bring above average temperatures and precipitation. During strong El Niño phases, the cold air remains too far to the north, leaving us with more rain events than snow (see photos 1 and 3 in photos tab).

It is during the weak and moderate El Niño seasons that we have above average snowfall totals (see photo 2 in photos tab). The Blizzard of 2009, in a moderate El Niño phase, broke several records for snowfall in the Valley and along the Interstate 95 corridor. The President's Day Storm of 2003 was also in a moderate El Niño phase.

However, we can have above average snowfall seasons during neutral years. The chart (see photo 4 in photos tab) shows that the majority of our heavy snowfall seasons occur in El Niño phases. Neutral phases have provided the D.C. Metro area with a few high snowfall seasons.

Moderate El Niño phases place the Valley in prime position for above average snowfall seasons. The extra warmth and moisture generated in the tropical Pacific is carried over to the Gulf of Mexico, where many of our snow-maker storms are generated. If enough cold air is in place, we get the perfect setup for big winter storms.

Information provided by J. Klein, National Weather Service Baltimore/Washington, Local Research
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