305
FXUS10 KWNH 170505
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1205 AM EST TUE DEC 17 2019
VALID DEC 17/0000 UTC THRU DEC 20/1200 UTC
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR
INGEST...
00Z NAM/GFS EVALUATION WITH PRELIMINARY PREFERENCES AND FORECAST
CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
..EASTERN CONUS
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z NAM, 00Z GFS, 12Z ECMWF BLEND
CONFIDENCE: SLIGHTLY ABOVE AVERAGE
NO MAJOR DIFFERENCES NOTED ACROSS THE EASTERN U.S., CONCERNING A
SURFACE LOW AND TRAILING COLD FRONT TO SLIP JUST SOUTH OF THE NEW
ENGLAND COAST TUESDAY NIGHT. THE 12Z UKMET'S SURFACE LOW WAS A BIT
MORE OFFSHORE THAN THE LATEST DETERMINISTIC/ENSEMBLE CLUSTERING.
THE 12Z UKMET AND 12Z CMC ARE ALSO SLIGHTLY SLOWER THAN THE
CONSENSUS REGARDING A DEEP CLOSED MID-LEVEL LOW TO CROSS NEW
ENGLAND ON WEDNESDAY BUT THESE DIFFERENCES SHRINK AS THE CENTER OF
THE CLOSED LOW MOVES INTO THE CANADIAN MARITIMES THURSDAY MORNING.
OVERALL, A 00Z NAM, 00Z GFS, 12Z ECMWF BLEND LOOKS REASONABLE, BUT
THE 12Z UKMET/CMC MAY ALSO HAVE UTILITY AT TIMES.
..WESTERN TO CENTRAL CONUS MID-LEVEL TROUGH
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z CMC / 12Z ECMWF BLEND
CONFIDENCE: AVERAGE
TIMING DIFFERENCES SHOW UP RATHER EARLY WITH A 500 MB TROUGH
REACHING THE CALIFORNIA COASTLINE EARLY WEDNESDAY MORNING WITH THE
00Z NAM SLOWEST. BY WEDNESDAY EVENING, THE 00Z GFS BEGINS TO EDGE
OUT AHEAD OF THE REMAINING DETERMINISTIC GUIDANCE. THROUGH FRIDAY
MORNING, THE 12Z ECMWF AND 12Z CMC FAVOR THE PREFERRED MIDDLE
GROUND WITH THE 12Z UKMET ON THE SLOW SIDE OF THE LATEST ENSEMBLE
GUIDANCE. TRENDS IN THE ENSEMBLES HAVE BEEN A BIT INCONSISTENT
WITH SLOWER TRENDS REGARDING THE MID-LEVEL TROUGH AXIS THROUGH THE
12Z/15 CYCLE, FOLLOWED BY A QUICKER TREND WITH THE 00Z/16 CYCLE
AND A SLOWER TREND AGAIN FOR THE 12Z/16 ENSEMBLE CYCLE. GIVEN SOME
OF THE SHIFTING, PREFER TO STAY TOWARD THE MIDDLE, AGAIN, CLOSER
TO A 12Z ECMWF/CMC BLEND.
..ONSHORE FLOW INTO THE PACIFIC NORTHWEST...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z NAM, 00Z GFS, 12Z ECMWF BLEND
CONFIDENCE: AVERAGE
A COLD FRONT WILL REACH THE PACIFIC NORTHWEST ON WEDNESDAY
FOLLOWED BY SURFACE LOW DEVELOPMENT ALONG THE TRAILING COLD FRONT
IN THE EASTERN PACIFIC THURSDAY MORNING. THIS WAVE WILL TAKE AIM
AT THE COAST OF WASHINGTON FOLLOWED BY THE ARRIVAL OF ITS TRAILING
COLD FRONT THROUGH FRIDAY MORNING. THE RESULT WILL BE A PROLONGED
PERIOD OF ONSHORE FLOW INTO THE PACIFIC NORTHWEST. MASS FIELD
DIFFERENCES ARE RELATIVELY SMALL BUT THERE ARE SOME TIMING
DIFFERENCES WITH THE SURFACE LOW AND FRONTAL TIMING INTO THE
PACIFIC NORTHWEST COAST. A FAVORED MIDDLE GROUND NEAR THE ENSEMBLE
MEANS IS SUPPORTIVE OF A BLEND OF THE 00Z NAM, 00Z GFS AND 12Z
ECMWF. CONFIDENCE IS AVERAGE GIVEN RELATIVELY GOOD AGREEMENT WITH
THE TROUGH PLACEMENT BUT ONLY FAIR AGREEMENT WITH THE SURFACE LOW
AND FRONTAL TIMING.
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.HTML
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML
OTTO
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