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Central PA OMG SNOW thread -- Winter 2016


neff

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LARGE SCALE DETAILS CONTINUE TO BE WELL AGREED UPON WITH THE WAVEPLACEMENT AND GENERAL DEPTH/STRENGTH AS IT CUTS OFF OVER ACROSSTHE LOWER MISSISSIPPI RIVER VALLEY DEVELOPING A SURFACE LOW INTOTHE CENTRAL TENNESSEE RIVER VALLEY BEFORE TRANSITIONING TO ACOASTAL LOW ON FRIDAY.  LARGER SPREAD EXISTS WITH THE TIMING ANDPLACEMENT MAINLY WITH THE TRANSITION TO THE COASTAL LOW DRIVENMAINLY BY THE INTERNAL SHORTWAVE FEATURES AND THERMALSETUP...CAUSING A GOOD SPREAD IN IMPACT DIFFERENCES MAINLY ACROSSSOUTHERN NEW ENGLAND AND FAR NORTHWEST MID-ATLANTIC BY DAY 3.  THEENSEMBLE MEANS CONTINUE TO PERFORM MOST CENTRALLY WITH FAIRLYSTRONG AGREEMENT THOUGH THE 00Z ECENS MEAN IS INITIALLY SOUTHACROSS THE LOWER MISSISSIPPI RIVER VALLEY IT COMES BACK TOAGREEMENT WITH ITS PRIOR RUNS INTO THE CAROLINAS; THE 06Z GEFS ISFURTHER NORTH BUT NOT AS DRAMATIC AS THE 12Z GFS WHICH AS SHIFTEDFASTER THAN ITS 00Z RUN AND MUCH OF THE GEFS MEMBERS...MAKING ITSEEM A BIT LESS LIKELY.   THE 12Z NAM REMAINS QUITE STRONG WITHTHE INTERNAL FEATURES AND IS A NORTHERN MEMBER ACROSS THE TNVALLEY BUT IS ALSO CLOSER TO THE 12Z GFS INITIALLY BUT AS THE WAVETRANSITIONS TO THE COAST REMAINS CLOSE TO THE GFS UNTIL ABOUT24/00Z WHEN THE SURFACE CYCLONE PIVOTS OFF THE DELMARVA...WHEN ITHANGS BACK WITH THE ECMWF.   THE 00Z ECMWF IS CLEARLY THE SLOWESTOF THE GUIDANCE AND THOUGH NOT A DRAMATIC OF A DIFFERENCE BY DAY 3AS THE GFS IS FROM THE GEFS... THE 00Z RUN REMAINS ON THE SLOW ANDSOUTHWEST EDGE OF THE ECMWF ENSEMBLE MEMBERS TO FAVOR IT OUTRIGHTEITHER.  THE 12Z UKMET PARTICULARLY EARLY (THROUGH DAY 2) SEEMS TOBE A GOOD MIDDLE GROUND TO THE ENSEMBLE MEANS...THOUGH BY DAY 3THE SURFACE LOW OCCLUSION MAY BE A BIT TOO FAR SOUTH AND WEST.  ASSUCH WILL CONTINUE TO HEAVILY FAVOR THE GEFS/ECENS MEAN ASPREFERENCE.  CONFIDENCE IS AVERAGE...AS THE SYNOPTIC IS IN GOODAGREEMENT BUT THE INTERNAL WAVE DIFFERENCES (WHICH AFFECTSMETEOROLOGICAL IMPACTS) REDUCE CONFIDENCE IN THE MESOSCALE/STATELEVEL IMPACT DIFFERENCES. 

http://www.wpc.ncep.noaa.gov/discussions/hpcdiscussions.php?disc=pmdhmd

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Something to keep in mind here, that looking at QPF output on these models, even with the sharp cutoff, can still sometimes mislead what will be the final snowfall distribution.  Often with these systems there is a snowfall maximum along the NW periphery of where the CCB and deform banding sets up.  This is where the best combo of moisture and ratios meet usually.  ALso often the banding along the northern edge can be enhanced by the warm conveyor belt running into the confluence to the north.  THus the sharp cutoff with the subsinance to the north of that banding cutting things off quickly.  In my experience this snowfall max usually sets up somewhere around the edge of the 1" qpf area and then things cutoff quickly once outside that.  Figuring out where that is can be tricky as the models are converging on a solution that puts that cutoff right across PA.  I think the southern border counties are pretty safely inside that zone.  Somewhere near or just north of the turnpike seems to be where that cutoff may set up right now.  Not saying north of there wont get snow, just more models totals versus the 15-20" totals likely south of that cutoff. 

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Fwiw hearing GEFs aren't great, and many send low due east from NC coast.

They haven't been good for a while actually, they were trending south each run the last 2 days but no one seemed to notice, or pay them much mind.  The 12z didnt really shift south as much as held steady with the last run which already was pretty bad.  For the record this was the break down

8 are big hits and get the 1" qpf well into central PA

7 get 1" qpf at least to the mason dixon and into the southern tier counties

3 get the .5 qpf at least into the southern tier

3 are total misses to our south or only skirt southern PA with very light snow

That breakdown is actually a little better then the 6z and even the 0z with numbers of misses but the mean dropped some because we lost 1 or 2 really crazy stupid members that were putting out 2.5" qpf way up into northern PA.  I think the gradient is starting to show itself and right now its around the turnpike.  These STJ originating systems often trend north the last 24-36 hours though so places north of there arent out of it yet.

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hr 78 more moderate snow into southeast pa than 0z - low occluded?

hr 84 again more moderate to heavy snow across southeast pa than 0z - once again york/lancaster in great spot (I really think cashtown is looking great with dynamics/topography across all models)

hr 90 still snowing across east pa - not as heavy banding in MD/south (for just this 6 hour period, not to confuse the lashing MD/south get in the 12-18 hours prior) as it is more north and east to give NJ/NYC some hope

hr 96 ending for most of pa outside of Philly quicker than 0z

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Big shift north on the ECMWF 

 

Looks pretty darn good for these parts. 

 

Wouldn't be shocked if we saw some Blizzard Watches tomorrow. 

I cant wait to see what the mesoscale models do as we get closer because the upper level dynamics continue to be impressive as hell

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Also of note, the later start on the Euro. Flakes don't fly in the LSV until early Saturday...worst arrives Saturday afternoon. Front end thump seems like it won't be much of a factor, as the orientation and track doesn't look right for that on the Euro. Our forum will be counting on what the CCB does on the north/northwest side of the low. It has trended in our favor and there is still time to go. 

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very sharp cutoff again, edge starting to show itself but good run for southeastern 1/3 again.  These are quick glance qpf numbers

LNS 1.9

York 1.9

ABE: 1.0

RDG: 1.3

MDT: 1.4

UNV 0.1

very very sharp cutoff from 1" to almost nothing in just 20-30 miles runs from just NW of garrett county MD northeast to near east stroudsburgh PA.  worrying about exactly where it is on each run is pointless until we are within 24 hours but thats about where it is on this run. 

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Does it get heavy stuff up past Harrisburg - or does it hit the turnpike and very quickly degrade as you move N/W from LNS?

it gets past the turnpike this run, a litle further then 0z but it does hit a wall not far past there.  This gets MDT into it a bit but its not by much.  SHARP cutoff just NW of there. 

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