Margins, Margins!

If you don't catch the subtlety of the title, it comes from a movie that runs for 24 hours on December 24th and 25th with regards to a "theme" paper that was turned in by one Red Rider toting youngster.   It's also appropriate for the upcoming Saturday event because it's a marginal event for snow in the Delaware Valley but things could come together for a snowy end thump across parts of the region, especially the farther north one resides.

Computer guidance has been relatively consistent in bringing energy from the Deep South on northeast along a frontal zone and into our region early on Saturday.   While the event will be a mixed bag event as milder air surges northeast aloft and somewhat at the surface, the energy will intensify and develop into a low pressure center over the Mid Atlantic as it continues its northeast trek.   Some of the computer guidance is trying to spit out a rapid intensification and as a result the stronger solution could yield more snow...and snow a bit closer to the region...on Saturday afternoon and evening.

For now, precipitation starts as a mixed bag of snow and freezing rain before temperatures rise above 32 and we transition into a period of plain rain for much of the region except perhaps the Lehigh Valley and the 222 corridor, which may have issues getting above 32.  The Poconos may transition to a mixed bag of sleet and freezing rain for a time during the event as temperatures at the surface stay cold enough to avoid going above 32 degrees.

As that low develops and intensifies, colder air drains back in on the west side of the low track and the intensification allows for enhancement of precipitation, especially on the north/west side of the low track.   The NAM above hints at the development of precipitation across Central Pennsylvania and quickly enhances as it lifts northeast.  

One thing we'll need to watch is the trend in guidance over the next 36 hours -- guidance has trended a bit colder and off runs of the NAM have been trying to blow up the snow a bit more suddenly.   This could catch some folks north/west a bit off guard if the faster development does take hold -- especially since this hasn't been talked up much thanks to the big icing event.   We'll have to see how that interaction between upper level energy coming in from the west and the surface wave play out.  

For now, we're projecting a coating to an inch of snow and slop along I-95, with 1-3" of slop and snow to the north/west of the city.   Around town, we're projecting a brief period of snow and mix before a transition to rain takes hold.   It's also possible we skip snow and go directly to a mixed bag of sleet and freezing rain for a time before temperatures rise above 32.   North and west should see a bit longer period of snow and I've also accounted for the potential that snow could be on the backside of the storm.   Farther north, 3-6" of snow is currently forecast.

Things could change -- perhaps for the snowier to the north of town.