455
FXUS10 KWNH 081655
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1155 AM EST SUN DEC 08 2019
VALID DEC 08/1200 UTC THRU DEC 12/0000 UTC
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR
INGEST...
12Z MODEL EVALUATION WITH PREFERENCES AND FORECAST CONFIDENCE
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..OVERALL PATTERN ACROSS THE CONUS
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PREFERENCE: BLEND OF 00Z ECMWF, 00Z EC ENS, 12Z GFS, 12Z NAM
LESS WEIGHT ON GFS AND NAM BY DAY 3
CONFIDENCE: AVERAGE
MODEL DIFFERENCES BEGIN TO EMERGE MORE SUBSTANTIALLY AROUND MONDAY
NIGHT WHEN A SOUTHERN STREAM TROUGH EJECTING INTO THE SOUTHERN
PLAINS WILL BEGIN TO INTERACT WITH AN EXPANSIVE TROUGH OVER MOST
OF THE EASTERN HALF OF THE COUNTRY. THESE DIFFERENCES STEM FROM
VARIATION IN THE STRENGTH OF THE SOUTHERN STREAM WAVE ITSELF, TO
THE PRECISE TIMING OF THE EJECTION TO THE EAST-NORTHEAST. THE
DIFFERENCES ARE NOT EXTREMELY LARGE, BUT THEY DO HAVE NOTABLE
IMPACTS ON THE FORECAST GIVEN THE POTENTIAL FOR TRANSITION OF
PRECIPITATION TYPES BEHIND THE ACCOMPANYING SURFACE COLD FRONT.
THE MODEL PREFERENCE IS WEIGHTED MOST STRONGLY TOWARD THE 00Z
ECMWF AND 00Z ECMWF ENSEMBLE MEAN. THEIR MASS FIELD FORECASTS ALSO
HAVE RELATIVELY GOOD AGREEMENT FROM THE 12Z GFS, SO THAT IS ALSO
INCORPORATED. HOWEVER, THE GFS HAS A MUCH LIGHTER PRECIPITATION
PATTERN DESPITE PWAT VALUES IN THE WARM SECTOR EXCEEDING THE 90TH
PERCENTILE FOR EARLY-MID DECEMBER, AND THE STRENGTH OF THE UPPER
LEVEL JET ABOVE THE 95TH PERCENTILE. THEREFORE, THE GFS DID NOT
RECEIVE AS MUCH WEIGHT IN THIS MODEL PREFERENCE, AS MOST OTHER
MODELS GENERATE MORE QPF.
THE 12Z NAM EJECTS THE WAVE FASTER AND PHASES IT WITH THE
LARGE-SCALE TROUGH MORE QUICKLY. IT ALSO HAS A COLDER LOW-MID
LEVEL TEMPERATURE PROFILE. THIS SEEMS TO BE PARTIALLY DUE TO A
FORECAST OF A STRONG FRONTOGENETIC CIRCULATION AND ASSOCIATED
COOLING WITH THE ASCENDING BRANCH. THE STRONG FRONTOGENESIS IS
PRESENT IN THE OTHER MODEL FORECASTS, AND THUS THE NAM SCENARIO
REMAINS PLAUSIBLE. NEVERTHELESS, THE NAM RECEIVED LESS WEIGHT IN
THIS MODEL PREFERENCE DUE TO DIFFERENCES WITH THE MID-UPPER LEVEL
MASS FIELDS FROM THE DOMINANT MODEL CONSENSUS.
OTHERWISE, THE 00Z CMC AND UKMET ARE NOT INCLUDED IN THE
PREFERENCE. THE UKMET, LIKE THE NAM, IS FASTER WITH THE EJECTION
OF THE SOUTHERN STREAM WAVE AND ALSO GENERATES CONSIDERABLY MORE
PRECIPITATION IN THE NORTHEAST. THIS HAS LESS SUPPORT FROM THE
ENSEMBLE DISTRIBUTION. THE CMC MAINTAINS A MUCH STRONGER SOUTHERN
STREAM WAVE, WHICH ALSO HAS LIMITED ENSEMBLE SUPPORT.
SEVERAL OTHER WAVES WILL DIG INTO THE WESTERN U.S. BY MID-WEEK,
AND MODELS DIFFER ON THEIR STRENGTH. THE PREFERENCE IS TO LEAN
TOWARD THE ECMWF AS IT IS CLOSEST TO THE ENSEMBLE MEANS.
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.HTML
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML
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