Saturday, January 21, 2012

Blogging Through Saturday Morning's Snow & Ice

More information available on twitter through the morning and midday.

As the second wave moves in at 7:30, sleet is the main precipitation type in the western burbs as milder air has jumped in aloft.  However, in heavier bursts of precipitation within the band we're seeing snowflakes drag down to the ground and getting anywhere from a 50-50 mix of snow and sleet to even mostly snow for those farther north of 422.   Temperatures at the surface are still subfreezing and will likely remain that way through the duration of the event.  This mixed bag of precipitation will move through the Pennsylvania suburbs, with a snow/sleet mix possible even into the Lehigh Valley as the second wave moves through over the next few hours.  Freezing rain will probably be the bigger issue along I-95 and in immediate South Jersey above the NJ Turnpike/295 with the second wave as it moves through although sleet will mix from time to time as well.   Snowfall totals through 7 AM are generally in that 1-3" range that we discussed in our 7 AM update.

Wave #2 should taper off between 11 AM (far west) and 2 PM (east) with some additional accumulation in terms of snow...this second wave will be a sleety compote that will pack down our fluffy snows from early this morning.   We might coax another inch or two out of the batch, especially for those that are getting more snow than sleet...but with the sleety mess in the mix I wouldn't be surprised if accumulation totals are held in check over the duration of the event...

Lighter precipitation  -- freezing drizzle and sleet -- generally is falling over Philly and South Jersey at this hour as the first slug of precipitation has moved away.  The second round sits back west of the suburbs and is about an hour or so away from picking up in intensity around here.   For those who are above freezing already or about to go above freezing -- you will see this second round fall in the form of rain.  Those along and northwest of 295 will have a myriad variety of precipitation types to deal with.   Snow is most likely in the Poconos and Lehigh Valley, with a mix of sleet and snow from the Pennsylvania Turnpike north to the edge of the upper burbs (basically Quakertown-Reading as the northern extent), with a mixed bag of sleet and freezing rain, mixed with snow in higher elevations south of the PA Turnpike to 295.

Snowfall totals as of 7 AM generally range between one and three inches for most of the region -- highest totals are in the northern and western suburbs, New Castle County in Delaware, and the Lehigh Valley.

The changeover to non-snow is taking place in parts of the region at this hour.  Philly has started to mix with sleet (at the Airport at least), and freezing rain is now reported in Millville and also in Harrisburg to the west.  Warmer air aloft is working in...and the surface down to our south continues to moderate as well as temperatures are now up to 40 in Southern Delaware and in the mid 40's down in Ocean City, MD.  That warmer air will stay away from the city proper at the surface but we will continue to see moderation in temperatures aloft over the next few hours.

The next heavier wave of precipitation is working into Central Pennsylvania and into Maryland -- this will work east over the next couple of hours and we should see a heavier/steadier burst of precipitation after 8 AM across the Philadelphia metro, probably a mixed bag of sleet/snow in the city and immediate north/west burbs (below the PA Turnpike), with freezing rain and some sleet in South Jersey between the Delaware River and the NJ Turnpike up to exit 6.  Above the PA Turnpike, we could see more snow than non-snow although sleet and perhaps freezing rain will mix in the lower elevations of the suburban counties in PA.

Snowfall is continuing across the city, South Jersey, and points north of there as the dryslot that I talked about earlier this morning has moved into Delaware. Temperatures are now above freezing in Atlantic City, with the rain/non-rain line generally extending from Wilmington around south of Millville to Atlantic City, with Wilmington having transitioned over to light freezing rain as of 5 AM.  I would expect as precipitation tapers off south of the city over the next couple of hours to see temperatures aloft rise up a bit and go above freezing.  There is more precipitation back across West Virginia and Western Pennsylvania that is about 3-4 hours away from us -- when that moves through later, it will be primarily liquid for folks south of the city and east of I-295 in Jersey...whether it falls as sleet, snow, or freezing rain north/west sorta remains to be seen based on how much slackening in precipitation takes place north/west of I-95 over the next couple of hours and how much warming takes places aloft.

Snow's flying early this morning for many above a Dover-Avalon line as the first thump of winter is moving on in.  Accumulations are in the inch or so inch range above the Garden State Parkway in Jersey, with a couple of inches in the higher hills in the northern & western suburbs of Philadelphia.  The first thump of snow is not surprising...probably a lil bit surprising at the Shore as temperatures have held cooler aloft a lil bit better than expected.  However, freezing rain is reported at Dover at 4 AM...a sign that warmer air is trying to work in.

You can see on the above radar picture that precipitation cuts off to the southwest of Wilmington in Maryland.  This dryslot will work east over the next few hours and cross Delaware and South Jersey, with precipitation tapering off to lighter snow, which will likely transition over to freezing drizzle and light sleet for those of you south of the city.  The lighter precipitation will not be able to fight the effects of warming aloft...and we will see temperatures respond in kind both at the surface but also in the atmosphere as precipitation slackens off in a couple of hours south of the city.   Those of you that are in the city and points north should hold onto snow for at least a little while longer.  Latest higher resolution guidance is keeping the snow/no snow line generally along the river between Philly and South Jersey and then east along Route 70.   The Airport might waffle around between snow and a wintry slop in a couple of hours' time, with the majority of the city staying's a very close call at this point!