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Central PA Winter Cont'd cont'd


The Iceman

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MODEL DIAGNOSTIC DISCUSSION

NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD

1137 AM EST WED FEB 15 2012

VALID FEB 15/1200 UTC THRU FEB 19/0000 UTC

...SEE NOUS42 KWNO ADMNFD FOR THE STATUS OF THE UPPER AIR INGEST...

12Z NAM/GFS EVALUATION AND PRELIMINARY PREFERENCES

...SHORTWAVE TROUGH OVER THE N. PLAINS...

PREFERENCE: GFS OR ECMWF

THE NAM IS A BIT FASTER AND STRONGER THAN THE GFS/00Z ECMWF AND

ONLY HAS SUPPORT FROM THE 00Z UKMET. THUS...THE NAM IS CONSIDERED

A LOW PROBABILITY SOLUTION. OTHERWISE...

THE GFS/ECMWF SOLUTIONS ARE COMPARABLE.

CONFIDENCE: ABOVE AVERAGE

...SHORTWAVE TROUGH OVER WEST TEXAS...

LARGE-SCALE MODEL FORECASTS ARE SIMILAR.

...SHORTWAVE TROUGH ENTERING THE PLAINS/MIDWEST FRI-SAT...

PREFERENCE: ECMWF

THE GFS APPEARS TO HAVE WORSE INITIALIZATION OF THE TROUGH'S

PLACEMENT OVER BRITISH COLUMBIA AND NUNAVUT THIS MORNING COMPARED

TO THE NAM/ECMWF. MEANWHILE...THE GFS IS MOST AGGRESSIVE IN

ALLOWING AN UPSTREAM PERTURBATION CURRENTLY OVER THE PACIFIC TO

CUT THROUGH THE SHORTWAVE RIDGE OVER THE CANADIAN ROCKIES ON

THURSDAY...WHICH THEN PHASES WITH THE NORTHERN STREAM AND SLOWS

THE ENTIRE GFS SOLUTION. THE COMBINATION OF WORSE INITIALIZATION

AND QUESTIONABLE AND EVEN SUSPICIOUS PHASING OF THE SEPARATE

STREAMS IS SUFFICIENT TO DISCARD THE GFS PARTICULARLY LATE IN THE

PERIOD. AMONG THE REMAINING SOLUTIONS...THE NAM BECOMES SLIGHTLY

FASTER THAN THE 00Z ECMWF/UKMET/CANADIAN WHICH ARE ALL IN

AGREEMENT. GIVEN THE NARROWER WINDOW FOR DATA ASSIMILATION IN THE

NAM VERSUS THE OTHER REMAINING SOLUTIONS...ALONG WITH THE

CLUSTERING OF THE NON-NCEP MEMBERS...THE PREFERENCE IS FOR THE

ECMWF.

CONFIDENCE: LESS THAN AVERAGE

...SHORTWAVE TROUGH OVER THE INTERMOUNTAIN WEST...

PREFERENCE: BEFORE 12Z FRI...NAM OR ECMWF

AFTER 12Z FRI...ECMWF

THE NAM BECOMES SLOWER AND REMAINS STRONGER...WHILE THE GFS

BECOMES MUCH FASTER LATER IN THE PERIOD COMPARED TO THE ECMWF

RESPECTIVELY...DUE IN LARGE PART TO DIFFERING DEGREES OF

INTERACTION WITH A SHORTWAVE TROUGH CROSSING TO ITS NORTH...WITH

THE GFS ACTUALLY PHASING WITH THE NORTHERN STREAM. DUE TO REASONS

DESCRIBED IN THE SYSTEM SECTION ABOVE...BOTH THE NAM AND GFS ARE

DISCOUNTED AFTER REACHING MEXICO...WITH A PREFERENCE TOWARD THE

ECMWF CAMP OF SOLUTIONS WHICH ALSO INCLUDES THE 00Z UKMET.

CONFIDENCE: LESS THAN AVERAGE

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

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So..how are we looking?

Better than we were 12 hours ago. GFS shows a major storm for true central PA (and for places SE albeit with p-type issues), and the ensemble mean has lighter precip but is colder. If the Euro is in agreement with the GFS I'll become a lot more interested, but as of now it's just a trend in a good direction.

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Eric Horst's update today:

"A light to moderate rain event is on tap for Thursday, but it's the potential for a weekend snow storm that has people talking today. The ingredients for an east coast storm have been on the table for a few days now, but the models have been wildly inconsistent in handling the complex split flow pattern. The northern branch disturbance for the possible weekend storm is still north of the Arctic circle, while the southern branch system is only moving into SoCal today...and will close off and track slowly through the southwest states the next two days. Timing and phasing of these two disturbances is at the heart of the matter...and it's just too early to believe any given model solution (although some forecasters will surely wishcast and jump on the snowiest possible solution). So instead of reading the models, I choose to read the pattern...and the pattern this winter has favored Pacific storms taking charge of the outcome in the East. This trend would favor a storm coming farther north and west--rather than missing off the southeast coast--and so I feel there's reason to believe that a storm may affect the mid-Atlantic region this weekend. Still, how far north/west the precip will make it and how much cold air is available to generate snow (rather than rain) across the region are details that won't likely become known until Friday. So as of midday Wednesday, I prefer to talk about the potential for some snow here on Sunday rather than making an outright forecast for snow. Stay tuned..."

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Reading about shortwave issues with the 12z gfs and it should be thrown out as result? Any redtags weighing-in?

GFS has had issues with how to deal with strength/speed/phasing of shortwaves for quite some time now. I wouldn't say you can throw it out just because of that though, otherwise why even look at that model. It's not like the operational is showing one thing and the ensemble members another. Several ensemble members show some form of a storm. I dont' think we can throw out either GFS or Euro just yet, just need to wait a little longer. The way this "winter" has been, the models really have not shown agreement on any big system until within 48-72 hours. Hopefully 0z tonight and 12z tomorrow will help one way or another.

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