Tuesday, February 28, 2012

An Array of Precipitation Type

Winter Weather Advisories are out for the Poconos for Wednesday with the incoming weather event that's currently in the Midwest.  While this storm tries to lift north, a strong area of high pressure over Canada will push it east and through our region on Wednesday, with precipitation moving in during the latter half of the morning commute and continuing through Wednesday evening before slackening off to drizzle and light precipitation.

Because of the high in Canada, chilled air will dam up against the Appalachians while warmer air works overhead aloft.  This will help enhance precipitation, yielding a steady if not moderate precipitation rates at times for many of us.  What type that falls from the sky is dependent on location.

The map above shows the precipitation breakdown for the region as of 10 AM tomorrow according to the NAM.  Keep in mind it's just one interpretation....but it and the Euro are pretty similar in alignment for precipitation type breakdown.

Poconos:  You go from snow to a mix of sleet and freezing rain in the afternoon, with some rain in lower elevations or places where temperatures are milder.   You will experience the best snowfall accumulations in this event, generally an inch in the valleys to as much as four inches in the highest elevations.  Precipitation will transition over from snow to non-snow after 1 PM from the southwest, starting as snow after 8 AM.  The highest elevations may go sleet for a longer period of time than others as there may be a colder layer of air to work with.

Lehigh Valley/I-78/Berks:  A quick shot of snow that changes to a mixed bag of sleet and freezing rain around midday, transitioning over to rain quickly thereafter.  The hills could pick up an inch or two of snow and sleet accumulation, with the valleys picking up coating to an inch type totals.  Once you transition to rain you should stay as rain although temperatures up your way will be pretty close to the freeze/thaw point.

Above the PA Turnpike and I-195:  Generally a quick shot of snow and/or sleet that transitions over to rain relatively quickly.  The snowiest case is that you get a coating to an inch on the hills, a coating is possible in lower elevations.  It's more likely you start as rain or rain mixed with sleet unless you're in the highest elevations of these areas before shifting over and nothing accumulates at all.

Below the PA Turnpike and I-195:  You start as rain, perhaps mixed with sleet.  Generally a non-event unless you love cold rains.   Over the Delmarva and perhaps down towards Cape May a few rumbles of thunder area possible with the system.

Rainfall totals could reach or exceed an inch, especially south of Philadelphia.

The good news is that the models are showing Thursday as a progressively milder day for inland areas.  Temperatures may surpass 60 degrees south and southwest of Philadelphia.  Unfortunately, clouds may hang tight for many, especially north and northeast of the city...and a significant warmup in Trenton, the Shore, or even Philly might be tough to pull out.  Fingers crossed, however, that the storm system clears out in time and we can see some sun on Thursday afternoon!