Senin, 21 Februari 2011

Blogging Somewhat Through The Evening...

Update 7:45 PM: Low dewpoints are going to be a tough enemy for snow lovers tonight in Bucks and Northeast Philadelphia, where dry air is surging southward on the northern side of that moisture boundary that's outlined earlier. There's going to be a pretty sharp cutoff on the northern axis of snow and it's possible Northeast Philly gets little more than coating type accumulations while the Airport gets a couple inches, with 5" just south/west of the city. We're still a couple of hours from heavier snow moving in from the west but dry air is having a better time of it so far than the moisture is as the precipitation streams east. The "virgathon" continues for now...as the heavier precipitation reaches us the city (and especially south of the city) will probably see snow reach the ground much more readily.

Radar at 6 PM shows the first fingers of light snow and sleet reaching the ground.  It's been precipitating above us for over an hour but the atmosphere is having to overcome dry air creeping south from Canada in the wake of wave #1 this morning.  Dewpoints are a concern to the north of the city -- at 6 PM they're down to 17 in Pottstown, 15 in Doylestown, and lower than that farther north.   It's going to be tough to get snow to work through that atmosphere and reach the ground.   Some accumulations are possible north of the city but the dry air working down will eat away at radar-induced wishes of snow and will keep your totals lower.

The areas that will get the most snow will be south of the city, specially looking to set up on a line from Baltimore to Avalon.   The map below shows dynamic lift (red circles) between the 850 mb and 700 mb level.  There's a bit of a mid level boundary to our south tonight and that will act as the focal point for heavier snow to ride east along.   This means that places such as Wilmington and Dover could see the most snow.  Keep in mind that the dynamics will lessen as this works east so snowfall totals in New Jersey may be a bit less than they are in Delaware -- but I do believe 6" amounts are certainly doable in parts of Central Delaware overnight.

With the "main" batch of precipitation out in Western Pennsylvania as of 6 PM we're probably 4-5 hours from the steadier snows reaching the area.  It should overspread everyone by 11 PM (that includes New Jersey, earlier west and southwest of the city).   For those areas that are currently getting sleet pellets or flurries precipitation will gradually increase in intensity in the next few hours and gradually change to snow.

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