Tuesday, March 05, 2013

Updating Where We're At

Winter Storm Watches are out for portions of the area this morning -- Delaware and Chester Counties in Pennsylvania, New Castle and Kent Counties in Delaware, plus Salem and Cumberland Counties in New Jersey for Wednesday with the storm system. They're indicating the potential for three to five inches of snow in these areas.

Last night's modeling suggested a bit of a compromise developing between the GFS and Euro thinking for tomorrow's storm, with the NAM sort of going out on its own with a very ramped and amped storm solution, suggesting several inches of snow on Wednesday night.  It, along with the SREF (short range ensemble forecasting), make up the exceptions to the rule in terms of modeling thinking.  Most other models show what the Euro and GFS (in general) are showing...more precipitation south than north.

Contrast those two above images with the NAM (below), which is amping up the storm a bit more excessively than the other guidance, reflecting less influence from the northern Quebec high and allowing the storm to bomb out and nudge up the coast a bit more than other guidance.  The result is the scenario that paints several inches of snow along I-95...although the breakfast time run of the NAM has muted this potential somewhat (still snowier than the rest, though).

Those differences in track and precipitation alignment result in the differences between the Euro, GFS (and also Canadian modeling) with those of the NAM and the SREF regarding how much snow *may* fall.  The short range models become more reliable within 24 hours of the event so we may see these models nudge themselves closer to the GFS and Euro camp.  How much remains to be determined.

A couple of things we'll monitor through the day today:

1) Precipitation intensity in interior South Jersey and Delaware for tomorrow afternoon and evening.  This makes the difference between a couple of inches of snow and more.  Assuming this is where the precip banding sets up tomorrow evening, it's possible the "red zone" we outlined in our map will be shifted to the south a bit.  Millville to Dover looks like the potential zone of snow.  The banding areas will probably be where snowfall ends up a bit more robust than areas farther north.

2) Do we see any more movement in the northern edge of the heavier (greater than a half inch of liquid equivalent) precipitation shield or do the GFS and Euro show consistency through the day?   Also, how much shift (if any) takes hold in the NAM on precipitation shield.

We'll provide a full update on timing, detail, and an updated forecast this evening.