148  
FXUS10 KWNH 121830  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
130 PM EST SUN JAN 12 2020  
 
VALID JAN 12/1200 UTC THRU JAN 16/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z MODEL EVALUATION WITH FINAL PREFERENCES AND FORECAST CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
   
..LARGE SCALE PATTERN ACROSS THE CONUS
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-GFS BLEND  
CONFIDENCE: AVERAGE  
 
19Z UPDATE: THE 12Z ECMWF/UKMET/CMC STILL ARE SHOWING A SLOWER  
PROGRESSION OF THE POLAR VORTEX OVER INTERIOR WESTERN CANADA  
THROUGH THE PERIOD, SOLIDLY PUTTING THE GFS AS A FAST OUTLIER AT  
THIS POINT. THE 12Z CMC DID TREND A TAD FASTER TOWARD THE GFS  
SOLUTION, ROUGHLY A MIDDLE GROUND BETWEEN THE SLOWEST (ECMWF) AND  
FASTEST (GFS). THE NAM/UKMET LIE IN THE MIDDLE AS WELL. WITH THIS  
IN MIND, WILL STILL LEAN TOWARDS A NON-GFS BLEND PREFERENCE.  
 
A BROAD LARGE SCALE TROUGH IS EXPECTED TO DEVELOP OVER THE CONUS  
THROUGH THE NEXT FEW DAYS AS A RESULT OF A CLOSED, SLOWLY MOVING  
LOW SETTLES ACROSS INTERIOR WESTERN CANADA. A STRONG IMPULSE  
RIDING THE PERIPHERY OF THIS FEATURE LIFTS THROUGH THE CENTRAL US  
AND GREAT LAKES REGION MONDAY/TUESDAY FOLLOWED BY A COUPLE  
DIFFERENT SHORTWAVES MID WEEK (ANOTHER CENTRAL US SHORTWAVE AND  
THEN A PACIFIC NORTHWEST LOW).  
 
THE LARGEST AND MOST SIGNIFICANT MODEL DIFFERENCES ARE  
ATTRIBUTABLE TO THE POLAR VORTEX OVER WESTERN CANADA AND ITS  
PROGRESSION (OR LACK OF) EASTWARD IN THE INCREASINGLY SHEARING,  
ZONAL FLOW BY THE END OF THE FORECAST PERIOD. THE GFS HAS  
CONSISTENTLY BEEN SHEARING THE VORTEX TOO QUICKLY EASTWARD AHEAD  
OF ALL THE OTHER AVAILABLE GLOBAL DETERMINISTIC GUIDANCE. ITS 12Z  
SOLUTION REMAINS WAY AHEAD OF EVEN THE GEFS MEAN, WHICH IS ALSO  
CONSIDERABLY FASTER THAN THE NON-NCEP GUIDANCE AND THE 12Z NAM AS  
WELL.  
 
ACROSS THE PACIFIC NW TOWARD MID-WEEK, A STRONGER BUT ALSO MORE  
AMPLIFIED WAVE CROSSES THE ALASKAN PENINSULA AND UPPER ALEUTIANS  
LATE MONDAY INTO TUESDAY, A RELATIVELY FLAT DOWNSTREAM 'RIDGE' OR  
LACK THEREOF, ALLOWS FOR GREATER BUCKLING OF THE FLOW THAT THE  
LEAD PORTION OF THE WAVE SUPPORT STRONG CYCLOGENESIS BY LATE  
TUESDAY INTO WED NEARING 130W. MOST OF THE GUIDANCE NOW HAS  
CONVERGED ON THIS IDEA INCLUDING THE CMC. THE GFS IS A BIT FASTER  
BUT HAS TRENDED TOWARD THE CONSENSUS. A BLEND OF THE NAM/ECMWF  
AND GFS SEEMS APPROPRIATE BUT HEDGING TOWARD THE ECMWF/NAM GIVEN  
THE GFS MAY BE SHOWING FAST BIAS. UNCERTAINTY, IS OBVIOUSLY HIGH  
GIVEN THE PROGRESSIVE FLOW, BUT THE AGREEMENT EVEN AT 84HRS IS  
HIGH ENOUGH TO HAVE AVERAGE CONFIDENCE IN A NAM/ECMWF WEIGHTED  
BLEND.  
 
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.HTML  
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML  
 
TAYLOR  
 

 
 
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