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Central PA & The Fringes - Early March 2015


MAG5035

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Right at 5" as the precip is starting to shut off around here. Nice storm. 

 

:o Oh why must it be the 84-hour NAM....

 

 

Holy **** haha, with the -10 isotherm at 850mb cutting PA cleanly in half diagonally to boot. NAM'ed for sure. 

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This week is certainly looking eventful... I'm becoming quite concerned about the ice potential with the Tuesday/Wed system. Can barely call it a cutter anymore, looks more like a piece of southern energy that ejects out and a more dominant northern stream low that resides all the way up in Ontario (as in the Canada Territory Ontario, not the lake). Once again, utter lack of a surface (or 850/700) low tells me that it won't be cut and dry to say the least with the p-types over the commonwealth with this particular system. Broad SW flow and rising heights in response to the digging out west will certainly ensure warm air comes in aloft, but no strong surface low running to the lakes indicates to me that low level temps are probably going to anchor themselves near the freezing mark or below for a good part of this in the eastern 2/3s of the state in general and the central third in particular. Could set up a significant sleet/zr period in the central counties. Bulk of precip looking to come thru during the evening Tuesday helps the case for freezing rain if the surface temps are there. The NAM/SREFs have had a lot of sleet as well. In fact CTP grids for my point and click location are indicating 1-2 inches of it during Tuesday changing to rain or freezing rain Tue night. 

 

WPC probs for >.25" ZR are def supportive of winter storm watches potentially being needed for at least some of the central counties as noted in the map here:

 

post-1507-0-42268600-1425289007_thumb.pn

 

So there's that, and then it is beginning to look like at least the southern third to half of the region is going to be decently impacted by the second wave that runs the frontal boundary on Thursday. GFS on its own just skirting the southern tier with snow, European has at least moderate snow for the southern third of the state and the NAM/GGEM are hitting the majority of the state pretty squarely. Euro ensemble mean is a bit more expansive getting at least the southern half to two thirds of the state in moderate snows and more notably the GFS ensemble mean actually looks at lot like the Euro's ensemble mean. So my current assessment of the situation would be that from I-80 southward (at the least) is looking at the increasing potential of a sizable snowfall. Positioning of the frontal boundary is going to be very important for this second wave, as the corridor of heavy snow is likely not going to be extremely wide. But given the big time thermal gradient, this could be a pretty big snowfall for the folks lucky/unlucky enough to get it. 

 

Here's WPC day 3 probs of >4", which probably aren't encompassing the whole storm yet for PA. But there's the initial take. 

 

post-1507-0-37091700-1425290172_thumb.pn

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Thanks for those thoughts, MAG.  Looking like it could be a high-impact event here.

 

So I took a snow core this morning and melted it down.  I used the relatively undisturbed area on the north side of my apartment.  Depth was 10-16" over the area, so I found a spot at 12.5-13" and cored there.  Melted to 2.91" of liquid, which lines up pretty well with the precip totals for the area since January 6.  If we add another 0.75-1"+ tomorrow into Wednesday we are really setting ourselves up for problems if/when we finally have a warm rainstorm.

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Holy wind. Roads are rough in spots with snow being blown right back on them.

My point & click says areas of blowing snow today as well but our snowpack down here is solidly encased with at least 1/4" of ice. It was tough to bust loose in spots on the driveway this morning. Sledding is fantastic though.

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BGM morning AFD on the pending snow/ice threat:

 

MODELS HAVE SLOWED THE ADVANCE OF THE PCPN SHIELD TUE AS THE NEXT
SYSTEM APRCHS. XPCT SNOW TO BRK OUT FROM WEST TO EAST AFT 18Z.
XPCT A PRETTY GOOD SNOW BURST AS IT ARRIVES IN THE VERY STRONG
WAA PTRN BRINGING A SLUG OF GULF MOISTURE UP AND OVER THE COLD AIR
IN PLACE OVER THE FCST AREA.

CONTD STRONG WAA TUE NGT BRINGS MORE LIFT AND MOISTURE...BUT ALSO A
VERY WRM LYR AT AND ABV H8. BLO...VERY COLD AIR LOCKED IN PLACE BY
THE TERRAIN AND COLD AND SNOWY SFC. THIS WILL RESULT IN A PD OF IP
AND EVENTUALLY FRZG RAIN INTO EARLY WED.

FLOW BECOMES MORE WLY AFT ARND 09Z ENDING THE WAA AND LIMITING
THE LIFT. AS A RESULT...PCPN SHD BEGIN TO TAPER OFF AND SNDG
COOLS. BY 12Z THERE/S STILL AND ELEVATED WRM LYR...BUT PCPN WILL
BE SPOTTY. NAM SEEMS TO BE THE WARMEST OF THE MODELS BUT MODELS
MAY BE UNDER ESTIMATING THE TENACITY OF THE COLD AIR...ESP EAST OF
I81 AND OVER THE NRN ZONES. THOSE AREAS MAY NOT SEE 32F THRU THE
NGT.

AFT SUNRISE WED...DESPITE THE WEAK CAA...MIXING AND LIMTED SUNSHINE
SHD ALLOW TEMPS TO RISE INTO THE 3OS LVG SOME SCT RAIN AND SNOW
SHWRS.

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My point & click says areas of blowing snow today as well but our snowpack down here is solidly encased with at least 1/4" of ice. It was tough to bust loose in spots on the driveway this morning. Sledding is fantastic though.

A glaze on top of snow is the best. I remember back in Atlanta we got 6" or so with a .2" ish glaze and we couldn't leave our driveway for 5 days since it was so persistent (even with sun angles probably equal to April up here).

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What's NAM look like for event tmrw?

strongest warm air advection we have seen in quite some time... might be too warm to create significant icing in some of the far west and southeast PA... ponding in lower laying areas that will freeze over in the region with deep current snow/ice packs may be biggest threat.  Likely sleet to rain for many.

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strongest warm air advection we have seen in quite some time... might be too warm to create significant icing in some of the far west and southeast PA... ponding in lower laying areas that will freeze over in the region with deep current snow/ice packs may be biggest threat.  Likely sleet to rain for many.

I agree, especially in the LSV.

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