528
FXUS10 KWNH 291645
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1145 AM EST FRI NOV 29 2019
VALID NOV 29/1200 UTC THRU DEC 03/0000 UTC
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR
INGEST...
12Z MODEL EVALUATION AND PRELIMINARY PREFERENCES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
..DEEP CLOSED LOW FORMING IN THE PLAINS
..HANDING OFF TO A NORTHEAST COASTAL LOW ON DAY 3
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF 12Z GFS / 00Z ECMWF...EMPHASIS ON THE ECMWF
A DEEP UPPER TROUGH PULLING INTO THE PLAINS WILL SPAWN
CYCLOGENESIS, RESULTING IN A DEEP CLOSED SYSTEM THAT IS FORECAST
TO SLIDE EASTWARD THROUGH THE SHORT RANGE PERIOD. AS HEIGHT FALLS
CROSS THE APPALACHIANS WE SHOULD SEE A HANDOFF TO A NEWLY FORMING
COASTAL LOW / NOR'EASTERN ON DAY 3, MONDAY. IN RECENT DAYS THE
ECMWF AND ECMWF ENSEMBLE HAVE PROVEN MORE CONSISTENT AND SERVED AS
A BASELINE FOR THIS STORM. THE NCEP SOLUTIONS, HOWEVER, WERE
BECOMING MORE USABLE. THE 12Z NAM AND GFS SHOW A LARGE SCALE
EVOLUTION THAT IS VERY SIMILAR TO THE ECMWF. THE THERMAL FIELDS
ARE OF INTEREST, GIVEN THE ANTICIPATED WINTER WEATHER IMPACTS.
CERTAINLY BY 48 HOURS, 12Z SUNDAY, THE NAM STRONGLY INDICATES ITS
TYPICAL COLD BIAS, WITH 850 MB COLD AIR OF GREATER MAGNITUDE AND
MORE EXPANSIVE THAN THE OTHER MODELS. NOTING THAT THE THERMAL
FIELDS IN THE OPERATIONAL ECMWF ARE STRONGLY SUPPORTED BY THE
ECMWF ENSEMBLE MEAN, WE HAVE MORE TRUST IN THE EUROPEAN AS A
BASELINE. THE GFS LOOKS MORE REASONABLE THAN THE NAM IN THIS
RESPECT. THE MAIN QUESTION MARK IS SLIGHTLY WARMER AIR, 850-700MB,
THE GFS INDICATES ALONG THE WARM FRONT IN THE MIDWEST AND THEN
NEAR THE LOW TRACK THROUGHOUT ITS JOURNEY TO THE EAST COAST. IT
WOULD NOT BE UNUSUAL FOR AIR TO VERIFY A BIT ON THE WARM SIDE OF
THE SPREAD NEAR THE LOW TRACK, BUT FOR NOW WE WOULD PLACE A
MAJORITY EMPHASIS ON THE ECMWF.
..WESTERN U.S. AND NORTHERN ROCKIES/PLAINS
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF 12Z GFS / 00Z ECMWF...EMPHASIS ON THE ECMWF
ANOTHER DEEP TROUGH AND WET STORM SYSTEM WILL DIG INTO PLACE NEAR
THE WEST COAST. THROUGH MONDAY THIS SYSTEM SITS BENEATH MEAN
SHORTWAVE RIDGING OVER THE PACIFIC NORTHWEST, WITH NORTHERN STREAM
SHORTWAVES AMPLIFYING DOWNSTREAM OVER THE NORTHERN ROCKIES AND
NORTHERN PLAINS. LOOKING AT THE FLOW PATTERN ACROSS THE PACIFIC
AND NORTH AMERICA, THE 00Z ECMWF AND CANADIAN MODELS, AS WELL AS
THE 06Z GFS, LOOK QUITE SIMILAR. MOST OF THE FLOW FEATURES ARE
LARGE SCALE AND PREDICTABLE, BUT THE NORTHERN STREAM OFFERS SOME
CHALLENGING SHORTER WAVELENGTHS, AND INTERACTING SHORTWAVES THAT
GYRATE AROUND THE WEST COAST TROUGH DO PRESENT SOME QUESTIONS. THE
12Z NCEP MODELS BEGAN A TREND IN HOLDING ONTO THE DEFINITION OF A
TIGHT UPPER LOW THAT RETROGRADES SOUTHWEST OUT OF OREGON. THE NAM
SEEMS TO SHOW A MORE REASONABLE TREND, WHILE THE GFS WAS MUCH
SLOWER AND REPRESENTED A STARK CHANGE FROM ITS 06Z RUN. ON THE
OTHER HAND, THE NAM SOLUTION IS SO MESSY AND UNSUPPORTED IN THE
NORTHERN STREAM, THROUGH THE NORTHERN ROCKIES, THAT IT IS HARD TO
RECOMMEND IN OUR PREFERENCE. FORTUNATELY, THE NAM/GFS THERMAL
FIELDS ARE VERY SIMILAR TO THE ECMWF OVER THE WESTERN U.S., FOR
FORECASTING PRECIP TYPE. BUT FOR SHORTWAVE TIMING AND LARGE SCALE
FORCING, WE RECOMMEND EMPHASIS ON THE ECMWF.
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.HTML
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML
BURKE
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