Looks like the Mid-Atlantic region is leaning towards the colder and snowier side of normal for the upcoming winter of 2013-2014…
Recap of last winter Last winter featured warmer-than-normal conditions in the Mid-Atlantic region during December and January, but then temperatures slid to slightly below normal during February and well below normal in March. Perhaps the most memorable feature from last winter is that there, in fact, were no memorable snowstorms. While several small snow accumulation events did occur in the region, there were no significant storms last winter with anything above 4 inches or so. This winter, however, should feature some episodes in which the timing will be just right between cold air outbreaks, an active southern jet, and storminess to produce significant snow events.
There are three major factors that will play an important role in the winter weather around here:
- Lack of a strong El Nino/Southern Oscillation (ENSO) signal in the tropical Pacific Ocean
- Low solar activity that frequently leads to high latitude blocking and, in turn, Arctic air outbreaks for the central and eastern US
- Above normal snowpack across the Northern Hemisphere
Neutral ENSO signal in the tropical Pacific Ocean All indications are that the sea surface temperature (SST) anomalies in the tropical Pacific Ocean will stay rather close to neutral during the upcoming winter season. It is very likely that there will be not be a strong El Nino (warmer-than-normal SSTs) or La Nina (colder-than-normal SSTs) any time soon in the tropical Pacific Ocean and that tends to open the door for a bigger influence around here from another part of the world such as in the northern latitudes and the North Atlantic Ocean. A strong signal from the tropical Pacific Ocean would typically become the dominating factor with respect to Mid-Atlantic winter weather no matter what takes place elsewhere around the world; however, with a neutral signal expected this winter, it is time to look elsewhere.
Low solar activity and high latitude blocking Research has shown that low solar activity tends to lead to the formation of a blocking pattern in the high latitudes (e.g., Greenland) during winter months which, in turn, leads to numerous Arctic air outbreaks into the central and eastern US from central Canada. While we are actually in a period of solar maximum for the current solar cycle, #24, it happens to be one of the weakest solar cycles in many decades and low solar activity is expected to continue this winter. Indeed, a look at numerous analog years with low solar activity reveals an unmistakable signal for high latitude blocking during winter months. This type of blocking pattern can be tracked through an index called the North Atlantic Oscillation (NAO) which would typically turn negative in times of high latitude blocking, and I expect that to happen frequently during this upcoming winter season as this may turn out to be the most important factor of all.
Above-normal snowpack in the Northern Hemisphere An important source region for cold air in this part of the US during the winter season is Eurasia - on the other side of the North Pole - and studies have shown that when snowpack increases in that part of the world during the month of October, and is above normal at the end of the month, then Arctic cold air outbreaks are sure to follow during the subsequent winter months in the central and eastern US. Indeed, snow cover in Eurasia increased dramatically during October reaching above normal levels by the end of the month. In fact, the Eurasian snowpack reached the 4th highest level in the past 46 years and the entire Northern Hemisphere snow cover reached the 7th highest level in that same 46 year period.
Summary of Winter Outlook for the Mid-Atlantic Region: The Mid-Atlantic region will lean towards the colder and snowier side of normal with temperatures some 0.5 to 1.0 degrees below normal for the winter season (November through March) and snowfall at 100-140% of normal. Normal snowfall amounts (which should be the minimal amounts this winter) are as follows: 15” at DCA, 21” at BWI, 21” at PHL, 29” at Central Park, NY