12:20 PM (Wednesday) | *Accumulating snow threat continues for the region from southern Virginia to the Carolinas*
Paul Dorian
Accumulating snow is quite likely for much of the region from southern Virginia to the Carolinas on Thursday and Thursday night; map courtesy NOAA, tropicaltidbits.com
Overview
It has turned colder today across the Mid-Atlantic region and an even colder air mass will push in for tomorrow and Friday. At the same time, a large batch of moisture will push northeastward on Thursday and the combination of the fresh, cold air and moisture should lead to a significant snow event from southern Virginia-to-North Carolina-to-upstate South Carolina. As has been the case for much of the winter season, the corridor from DC-to-Philly-to-NYC will very likely escape without any appreciable snowfall, but there are some signs for more sustained cold and perhaps a better chance for snow as February winds down and March gets underway.
Accumulating snow for the Carolinas and southern Virginia
The right combination of a fresh, cold air mass and lots of incoming moisture will quite likely lead to a significant snow event on Thursday and Thursday night for the region from southern Virginia to the Carolinas. In fact, there is a good chance for 3-6 inches of snow in much of this region by the time Friday morning rolls around. Low pressure will develop along the Carolina coastline on Thursday and the fresh, cold air mass will be anchored by strong high pressure over the Mississippi Valley region. As has been the case for much of the winter, the snow will largely if not completely escape the region from DC-to-Philly-to-NYC, but there are some signs for a pattern change will could allow for more sustained cold air outbreaks and perhaps an increased chance of snow.
The teleconnection index known as the North Atlantic Oscillation (NAO) is showing some signs of going from positive-to-neutral in coming days; map courtesy NOAA
Signs of a potential pattern change for the eastern US
In terms of the longer-term outlook for cold and snow in the DC-to-Philly-to-NYC corridor, the bad news is that time is running short on this winter season. As we progress from late February into March, the seasonal averages for temperatures climb rather sharply from current levels meaning that any air mass that can be supportive of snow has to become more and more abnormally cold given the time of year. The good news for cold and snow lovers in the eastern US is that there are some signs for pattern changes across North America that could produce more favorable conditions as we progress from late February into early March.
The teleconnection index known as the Eastern Pacific Oscillation (EPO) is showing some signs of going from positive-to-negative in coming days; map courtesy NOAA
To begin, the pattern that has bottled up cold air over Alaska this winter season may be about to change some – at least temporarily. A trough of low pressure has been situated for much of the winter season over Alaska along with persistent high pressure to the south of there over the northern Pacific. This overall pressure pattern has generated a strong upper-level flow of air from west-to-east extending from the northern Pacific to the western part of Canada and into the northwest US. This type of upper-level pattern has frequently pushed mild air masses into western Canada and has also made it more difficult for cold air masses to drop southeastward from Alaska into the central and eastern US.
The last week of February promises to be colder-than-normal for much of the nation according to the 06Z GEFS; map courtesy NOAA, tropicaltidbits.com
One teleconnection index that provides us with information about the pressure pattern across the northern Pacific and Alaska is known as the Eastern Pacific Oscillation (EPO). When the EPO is in a positive phase, low pressure tends to dominate over Alaska with high pressure to the south and this generally results in strong winds blowing mild air eastward from the Pacific to western North America – the overall dominate pattern during the past several weeks. When the EPO index goes negative, high pressure ridging tends to develop over Alaska and it turns warmer-than-normal and cold air outbreaks tend to increase from central Canada into the central and eastern US which makes it more favorable for sustained cold and snow. The EPO is forecasted by some computer models to go into negative territory in coming days which could result in a more favorable pattern for cold and perhaps snow in the Mid-Atlantic region as we progress to late February and early March.
More sustained cold in the Mid-Atlantic region is a possibility as we head into early March; map courtesy NOAA, tropicaltidbits.com
In addition to the EPO, another teleconnection index known as the North Atlantic Oscillation (NAO) is forecasted to drop pretty sharply in coming days from positive territory to near neutral. This index along with its closely related cousin known as the Arctic Oscillation (AO) provide us with information about the pressure pattern in the North Atlantic Ocean. Similar to the EPO, a negative phase of the NAO is more favorable for sustained cold in the central and eastern US and this, in turn, adds to the chances of snow.
Final thoughts
Stay tuned on the prospects for sustained cold and snow in the eastern US in coming days as there have been many “false alarms” for pattern changes this winter season. As for now, the best chance for significant snow in the short-term is across the Carolinas and southern Virginia on Thursday and Thursday night as the perfect combination (perfect for snow lovers in that region) of cold and moisture will actually materialize.
Meteorologist Paul Dorian
Perspecta, Inc.
perspectaweather.com
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