Quick lunchtime update, but first a statement from the National Weather Service:
THERE IS SOME RAIN ON THE SOUTHERN PERIPHERY OF THE NORTHERN
STREAM SYSTEM ALSO IN PARTS OF WESTERN PA AND EASTERN OH. BASED
ON THE MEAN FLOW SEEN IN 12Z UPPER DATA…THE AXIS OF THE HEAVIEST
SNOW MAY BE SHIFTING EVER SO SLIGHTLY MORE WEST AND NORTH THAN
CURRENT FORECAST. LOTS OF CONVECTION OFF THE CAROLINAS WHICH COULD
CONTINUE THE ENHANCED DOWNSTREAM UPPER RIDGING THAT COULD SHIFT
THE SURFACE LOW TRACK AND ASSOCIATED RAIN/SNOW LINE AND DYNAMICS
JUST A SLIGHT HAIR WEST AND NORTH OF CURRENT FORECAST.
Translated, the storm appears tracking a little farther west than originally thought. Now, I know that many of you in the western portions of the area have seen nothing at all, and are thinking, ‘how can that be?’ The reason for this has to do with the low to our west – the sinking air between the coastal low and the western low effectively prevents any precipitation from occurring.
HOWEVER, the energy from the western low is currently being absorbed or phasing with the coastal low. This coastal storm is now undergoing rapid intensification, and there is intense convection over SE NJ moving NW at this hour. As the storm deepens and moves up the coast, the precip shield will expand northwestward. This will take some time, but snow should develop from southeast to northwest. Because the low may track slightly further west, this can shift some of the heaviest snows slightly west.
But, unfortunately, its not that simple. There will also be mesoscale banding developing, which in layman’s terms is where one town can get 2 or 3 inches of snow in an hour or two, and another a few miles away gets nearly nothing (again due to sinking air). There is no way to predict this ahead of time. Regardless, everyone in eastern PA will see snow this evening, with the most the farther east and north you go.
This is a complicated storm to say the least, but it is far from over, and in fact, is only just getting started. The heaviest snows will be occurring from late afternoon into the overnight hours. We’ll have more updates periodically as warranted. [doc]