While we are entering a noticeably milder stretch of weather in the Mid-Atlantic region for the second half of this week, there are signs for a return to a very cold weather pattern across the central and eastern U.S. by the middle and latter parts of next week. In fact, upcoming changes to the upper level atmosphere in the northern hemisphere resemble the overall pattern seen during the “polar vortex” cold air outbreak experienced earlier this winter.
The polar vortex is an area of cold low pressure that typically circulates and strengthens around the Arctic region in the wintertime and then weakens in the summer. During winter, pieces of the polar vortex can break off and be sent southward with the jet stream to either the Europe/Asia side of the North Pole or to North America. Meteorologists try to track the positioning of the polar vortex as a way of predicting Arctic air outbreaks that potentially could drop southward into the mid-latitudes. Computer forecast models can show the position of the polar vortex through their forecasts of heights of different atmospheric pressure levels. Last night’s European computer model 10-day forecast of the 500 millibar height field (~18,000 feet up in the atmosphere) clearly shows yet another example of the polar vortex being distributed to mid-latitudes – in this case to both sides of the pole (see forecast map above). This particular upper-level scenario is forecasted to occur in 10 days and it will likely be accompanied by much colder-than-normal air in the central and eastern US.
Not to be outdone, the main U.S. (NOAA) forecast model called the Global Forecast System (GFS) confirms this idea of future cold as it also has a very cold-looking overall weather pattern in the 7-10 time period that coincides with the European model forecast. Last night’s GFS Ensemble 500 millibar forecast map (below) for the 7-10 day time period features a deep trough of low pressure in the northeastern part of the U.S. (blue) and a strong ridge of high pressure (red/orange) extending northward along the west coast of the U.S. and Canada. The combination of the trough in the east and the ridge in the west will likely force numerous Arctic air masses to drop southward from central Canada into the central and eastern U.S. as we close out February and begin the new month of March – just as it did earlier this winter. In addition, the high pressure ridging that virtually surrounds the eastern trough is indicative of a “blocking” pattern in the upper atmosphere that promises to keep the cold air in place for awhile in the central and eastern U.S well into the month of March.
One final note...this winter has had a habit of generating snow at the front-end of a warm-up (e.g., this morning) and at the back-end of a warm-up (e.g. the snowstorm on the day after Super Bowl Sunday). If this pattern holds true, look out for possible significant snow in the early or middle part of next week as we transition back to a much colder-than-normal weather pattern.
[map courtesy Penn State eWALL]