Hi everyone.  It's another winter weekend with a lot of moving parts over the next few days so I'll try to break this next show down into manageable bites.  Here goes... In short - warm, then cold, then white, then REALLY cold then yetis.

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Tonight into Saturday (warm)

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We've got a warm front driving north through the area tonight that should help bring in some warmer air for the day Saturday.  Unfortunately, a bit of moisture is coming with it (not out of the ordinary) but there's a chance we might have a brief period of freezing drizzle in the early morning hours before everything warms up so if you're out early especially in the outlying areas where the air is cooler, be careful as there might be some slick spots.  If this temperature issue materializes, I suspect we might see some brief Special Weather Statements from the NWS to alert everyone to it. 

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Saturday should top out around 40F in the metro area while we're in this warm sector but by midnight, a much stronger cold front will sweep through from the west and usher in much colder air that will help set the stage for a snow event on Sunday.

 

Sunday (cold and white)

 

Sunday's storm is a great example of why I hate long range winter forecasts.  On the Wednesday morning model runs, there wasn't anything of concern at all and although conditions looked cold, a Nor'easter wasn't even on the scopes.  By Friday morning however, models showed a full-blown snowstorm set for Sunday afternoon almost purposefully aiming at the Eagles game (images at right).  Barely more than 72 hours in advance, things materialized and then models coalesced into a hefty Mid-Atlantic snowstorm.

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As the cold front whips through Saturday night, a low pressure center should form on its coattails over the Deep South and then angle up the Southeast until it moves offshore around the DelMarVA around 1 PM and due east of the Jersey shore by around 4 PM.  The pressure is not forecast to be exceptionally low on this one so I'm am not exactly expecting snowmageddon but the temperature profiles look like all snow for the metro area as of right now.  NWS has been discussing the potential for a mix to spread into the southern zones and perhaps as far west as Delco and Philly but I'm not seeing it in the soundings at the moment.  I DO see this nudge of warm air over a lot of NJ so there should be a rain/snow mix there to keep down accumulations.  Same for a lot of DE.  The warm air wedge is there around 4000-6000 ft. in the models over eastern PA too but there's just not enough of it at this point to make me think there will be a mix over the metro.  That could change of course but for now I'm thinking all snow. 

 

If there is no transition to a rain/snow mix, I think we'll see a healthy 6"-8" over most of the metro area especially north and west (typical for these coastal storms).  If the warm air aloft become thick enough to melt the snow on the way down, this will limit accumulations to the south and east and likely bring in some sleet and/or rain.  As for timing, snow should slowly overspread the region just about any time after dawn on Sunday and gradually increase with peak snowfall occurring between 1-6 PM (have fun Birds fans).  There could be some pretty heavy bursts in that timeframe as well so be prepared.  By dinner, things should taper off with all precipitation ending by midnight but road conditions will undoubtedly will not be great and depending on the result of the game, neither will the fan base.  So, I guess we'll just have to rely on that time-tested, experienced, even-keeled Philly response to winter weather events to get us through the day.

 

As of now, the NWS has left out Philly, Delco and NJ from the Winter Storm Watch since this is the region that could see the nose of warm air knock down accumulations.  Keep an eye on this especially the counties away from the coast.  At some point tomorrow, I suspect most of the current Watch zones will go to Warnings but there should also be some counties added into the Advisory/Warning regime depending on how the models see the warm air developing (or not).  If the warm air backs off, I think the rest of the metro area will also go to Winter Storm Warnings as we should exceed the snowfall totals to warrant that level of alert.  If the warm air looks like it'll nose in, Winter Weather Advisories are more likely so watch for this separation.

 

Monday (cue the yetis)

 

Behind the coastal storm, a massive dome of Arctic air will settle in from the northwest and bring the coldest air we've seen in quite some time.  With pressures up above 1040 mb., the only way you can get air density like that is to just suck all of the heat out of it and that is exactly what is going to happen.  Tuesday and Wednesday in particular look yeti-worthy with high temperatures not getting out of the teens.  On top of that, a steady northwesterly wind will persist throughout the period bringing wind chills down very close to 0F.    Snow cone anybody?      

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​​​​Another storm next week?

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This is worth keeping an eye on.  GFS is being pretty bullish about another Nor'easter forming in the Gulf of Mexico and then shooting across the southern states before going offshore.  As of right now, it looks like this storm should miss us to the south almost entirely but if the storm track shifts to the northwest as Sunday's has, we could be in for another round of snow mid-week.  Worth keeping an eye on but let's get past this first one.

 

Have a nice weekend everybody!

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rs

2152

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