911
FXUS10 KWNH 250633
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
132 AM EST WED DEC 25 2019
VALID DEC 25/0000 UTC THRU DEC 28/1200 UTC
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR
INGEST...
00Z MODEL EVALUATION WITH PREFERENCE AND FORECAST CONFIDENCE
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..OVERALL PATTERN ACROSS THE CONUS
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PREFERENCE: NON-NAM BLEND
CONFIDENCE: AVERAGE
---06Z UPDATE---
THE 00Z CMC HAS TRENDED CLOSER TO THE PRELIMINARY PREFERENCE (GFS,
ECMWF, UKMET) SUCH THAT IT IS NOW INCLUDED IN THE PREFERENCE. ITS
DEPICTION OF THE EVOLUTION OF THE PHASING WAVES IN THE ROCKIES NOW
LOOKS SIMILAR TO THE OTHER MODELS, AND THE SURFACE LOW POSITION IN
THE CENTRAL PLAINS BY 28.12Z HAS TRENDED NORTH CLOSER TO THE OTHER
MODELS. IT'S WORTH NOTING THAT THE 00Z GEFS MEAN LOW POSITION HAS
ALSO TRENDED NORTH.
---PREVIOUS DISCUSSION---
MODELS ARE IN RELATIVELY GOOD AGREEMENT WITH THEIR MASS FIELD
FORECASTS THROUGH THURSDAY AFTERNOON (27.00Z), AT WHICH POINT MORE
SUBSTANTIAL DIFFERENCES BEGIN TO EMERGE. ONE SIGNIFICANT SOURCE OF
MODEL VARIABILITY SEEMS TO BE A POTENT SHORTWAVE CURRENTLY NEAR
THE ALEUTIAN ISLANDS THAT WILL BECOME SHEARED OUT AND DIG INTO THE
NORTHERN ROCKIES BY FRIDAY. SMALL VARIATIONS IN THE EXACT
TRAJECTORY AND STRENGTH OF THE WAVE AS IT REACHES THE U.S. PRODUCE
LARGE DIFFERENCES DOWNSTREAM AS PHASING BEGINS WITH THE EJECTING
SOUTHERN STREAM CLOSED LOW IN THE SOUTHWEST.
THE 00Z NAM AND 12Z CMC SHOW A STRONGER NORTHERN STREAM WAVE THAT
FAILS TO COMPLETELY PHASE BY SATURDAY MORNING (28.12Z). BOTH
MODELS WERE NEAR THE EXTREME END OF THE ENSEMBLE ENVELOPE IN TERMS
OF AMPLIFICATION OF THE NORTHERN STREAM WAVE, AND THE 00Z GFS HAS
TRENDED SLIGHTLY LESS AMPLIFIED WITH ITS NEW RUN (CLOSER TO THE
ECMWF, UKMET AND ENSEMBLE MEANS). THEREFORE, THE PREFERENCE IS TO
LEAN TOWARD THE GFS, ECMWF AND UKMET AS THEY HAVE GREATER ENSEMBLE
SUPPORT AND ARE MORE REPRESENTATIVE OF THE TRENDS OVER THE PAST
COUPLE MODEL CYCLES.
NEVERTHELESS, THOSE THREE MODELS STILL HAVE FAIRLY SIGNIFICANT
DIFFERENCES WITH THEIR QPF. THE ECMWF, FOR INSTANCE, SPREADS
MEASURABLE PRECIPITATION WELL INTO THE DAKOTAS BY THE END OF THE
DAY 3 PERIOD, WHILE THE GFS IS MUCH DRIER THAT FAR NORTH (THE
UKMET IS IN BETWEEN THE TWO WITH RESPECT TO THE NORTHWARD EXTENT
OF PRECIP). THEREFORE, ALTHOUGH THE MASS FIELD PREFERENCE IS FOR A
BLEND OF THE GFS, ECMWF AND UKMET, THE QPF WAS TRENDED TOWARD A
COMPROMISE IN TERMS OF GEOGRAPHICAL EXTENT WHILE STILL MAINTAINING
SOME OF THE MAGNITUDE OF MAXIMUM AMOUNTS IN THE CENTRAL PLAINS.
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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