746   
FXUS10 KWNH 250437  
PMDHMD  
  
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1136 PM EST TUE DEC 24 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  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
   
..OVERALL PATTERN ACROSS THE CONUS  
  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 00Z GFS, 12Z ECMWF, 12Z UKMET  
CONFIDENCE: AVERAGE  
  
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  
  
LAMERS  
  
  
 
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