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Storm Threat Dec 26-28 Period


Ralph Wiggum

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Folks, this is a big development with the GFS run. You now can see that the primary low dies over Ohio and then a new takes shape just over eastern North Carolina. So, we are seeing how the block over Eastern Canada is keeping this storm from doing a Lakes Cutter. So, to me, I think we can see more of coastal development than what the models showed today. Still more time to watch, but you can here, that Eastern PA and up into New England would do pretty good with this storm.

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I usually wait for the run to come out on TwisterData but going off InstantWeatherMaps it appears that 189-192 is the window where we might actually see snow all the way down into Philly. 186 has 850's at ~2 C over Philly and a freezing line running through the far NW burbs.

Since this is inside truncation we can get a bit more detail in about 10 minutes when the raw data comes out and see who gets what off this run. Interesting feature showing up over DE on the 6-hour accum precip at 192 with a band of >0.50" QPF surrounded by only 0.10-0.20".

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As a FYI, I *think* the qpf on the GFS at 180-192 is previous 12 and not previous 6. The map will say 6 on SV but if you look at it and the NCEP graphic (which is previous 12 hours in the 180-192) you'll see similarities.

It's not quite truncated but the QPF is not just a 6 hr window...so any of that "snow" that's falling may be rain at 180 or rain ending as snow.

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completely different look on the 6z GFS. 12/26 system much weaker, flatter, develops a weak low along the coast off of the Carolinas but definitely nothing like the 0z.

thing goes all pat Burell on us. from apps runner to OTS lol.

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It's much stronger/further north with the Christmas wave which then affects the storm following.

The 500 responsible for Christmas is actually south of 0z (but north of 18z) and digs the wave a bit more while it flattens the 500 in the SW (which develops the supposed "bigger" storm).

The difference between 18z and 6z on the bigger storm is rather significant...the 18z digs the wave down to the AZ/Mexico border while the 6z only digs it down to, oh, Northeastern NEW Mexico. What's 400 miles between 2 model runs 12 hours apart? Oh, the difference between a snow/rain/ice fest and a weak wave that scoots out-to-sea.

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0z and 6z gefs have trended towards a faster secondary and make it pretty much a coastal with a good track...again this is stil 7 days away, but its getting to the time period where you start paying attention to trends...this isn't done trending at all.

Also, the stronger the 1st wave on christmas is the better shot the 2nd wave ends up further south. With a stronger first wave it reinforces the cold air, becomes a new 50/50 low and prevents big hgt rises along the coast. Though, the risk of the 1st wave being stronger also means it could be liquid.

0z

gfsensm-mslp-qpf_174.png?1355980355

6z

gfsensm-mslp-qpf_168.png?1356001966

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HPC starting to honk a bit.

EXTENDED FORECAST DISCUSSION

NWS HYDROMETEOROLOGICAL PREDICTION CENTER COLLEGE PARK MD

200 AM EST THU DEC 20 2012

VALID 12Z SUN DEC 23 2012 - 12Z THU DEC 27 2012

...MORE ACTIVE WINTER WEATHER COMING...

MODELS AND ENSEMBLES IN GENERAL OFFER AN INCREASINGLY SIMILAR

LARGER SCALE FLOW EVOLUTION FOR NEXT WEEK DESPITE CONTINUED

DIFFERENCES WITH EMBEDDED SYSTEM TIMING AND INTERACTIONS. THIS

PATTERN SEEMS HIGHLIGHTED BY LEAD MID-UPPER LEVEL TROUGH ENERGY

FROM THE CENTRAL TO ERN US DAY CHRISTMAS EVE/CHRISTMAS ALONG WITH

AN ASSOCIATED SURFACE SYSTEM REFLECTION AND PCPN FOCUS THAT THE

MODELS TRENDS NOW BETTER FAVOR INTO THE COOLED AIRMASS IN WAKE OF

THE DEEPER DOWNSTREAM CANADIAN MARITIME LOW.

UPSTREAM...AMPLE MID-UPPER LEVEL TROUGH ENERGY DIGS FROM THE WEST

COAST CHRISTMAS EVE TO THE S-CENTRAL ROCKIES/PLAINS BY CHRISTMAS

WITH SURFACE LOW DEVELOPMENT AND PCPN UNDERNEATH AND OVER SWD

SURGED PLAINS HIGH PRESSURE. THIS SYSTEM REALLY IS EXPECTED TO

DEEPEN MID-LATE WEEK OVER THE E-CENTRAL THE ERN US INTO A MAJOR

WINTER STORM WITH AN EXPANDING HEAVIER PCPN SHIELD. THERE IS

AMPLE ROOM FOR COLD AIR TO SETTLE TO THE NORTH OF THE LOW AND

DAMMED DOWN THROUGH THE MID-ATLANTIC IN ADVANCE OF THE SYSTEM.

OVERALL...HPC OVERNIGHT MEDIUM RANGE SURFACE FRONTS/PRESSURES AND

500 MB PROGS ALONG WITH NEW OVERNIGHT 00 UTC HPCGUIDE 5KM SENSIBLE

WEATHER GRIDS HAVE BEEN PRIMARILY DERIVED FROM A BLEND OF THE 18

UTC GFS WITH THE 12 UTC ECMWF/GEFS ENSEMBLE MEAN/ECMWF ENSEMBLE

MEAN. THESE MODELS OFFERED A REASONABLY SIMILAR LARGER SCALE

PATTERN EVOLUTION ALOFT AND CLUSTER THE MAIN SURFACE FEATURES

BETTER THAN OTHER AVAILABLE GUIDANCE. THE PURPOSE OF INCLUSION OF

THE ENSEMBLE MEANS WAS TO SMOOTH THE LESS PREDICTABLE SMALLER

SCALE DETAILS WHILE BLENDING IN THE GFS/ECMWF ALLOWS FOR BETTER

FEATURE DEFINITION FOR SEEMINGLY THE MORE PREDICTABLE FEATURES

GIVEN BROAD GUIDANCE SUPPORT. A QUICK LOOK AT THE LATER 00 UTC

MODELS SHOWS CONTINUED VARIABILITY WITH TIMING/SPACING OF EMBEDDED

INDIVIDUAL FEATURES BUT CONTINUED SUPPORT FOR THE OVERALL ACTIVE

WINTER PATTERN.

SCHICHTEL

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The christmas day storm is colder on the gefs, while the euro ens have it tracking right over the region...a little warmer obviously with the r/s line running over phl metro back yards.

euro ens for the 26-27 storm shifted a little east and a bit colder...The primary is a good bit weaker and you can see the transfer starting at hr 168

00zecmwfens850mbTSLPUS168.gif

00zecmwfens850mbTSLPUS192.gif

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Here is the latest 6-10 day forecast for the cpc...the 1st analog that particular date has nothing, but 6 days later was the christmas day storm that brough a foot plus in the pocs and 4-12 for the nw burbs and rdg to abe but the 2nd one dropped 13 inches of snow on philly...3rd analog dropped 5 inches on phl..

610analog.off.gif

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