352  
FXUS10 KWNH 271613  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1211 PM EDT MON APR 27 2020  
 
VALID APR 27/1200 UTC THRU MAY 01/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z MODEL EVALUATION INCLUDING LATEST PREFERENCES AND CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
   
..DEEP TROUGH/LOW CENTER EXITING THE NORTHEAST
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
THE MODELS GRADUALLY TAKE THE DEEP UPPER TROUGH AND ASSOCIATED  
CLOSED LOW IMPACTING THE NORTHEAST GRADUALLY AWAY FROM THE REGION  
THROUGH TUESDAY. THE GUIDANCE SHOWS RATHER MINIMAL MODEL MASS  
FIELD SPREAD AS THE SYSTEM EXITS AWAY, AND SO A GENERAL MODEL  
BLEND WILL BE PREFERRED.  
 
   
..NORTHERN STREAM TROUGH AMPLIFYING OVER THE MIDWEST
 
   
..SYSTEM ADVANCING INTO THE EASTERN U.S. BY THURSDAY
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF THE 00Z UKMET/ECMWF/ECENS MEAN  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
A NORTHERN STREAM SHORTWAVE TROUGH CLIPPING THE PACIFIC NORTHWEST  
AND SOUTHERN BRITISH COLUMBIA TODAY IS EXPECTED TO AMPLIFY  
SOUTHEASTWARD DOWN ACROSS THE MIDWEST BY WEDNESDAY IN RESPONSE TO  
A DEEP LAYER RIDGE DEVELOPING OVER THE WESTERN U.S. AND SOUTHWEST  
CANADA GOING THROUGH THE MIDDLE OF THE WEEK. THE GUIDANCE SHOWS A  
STRONG CLOSED LOW EVOLVING OVER THE MIDWEST WHICH WILL FOCUS ON  
THE OH VALLEY AND WESTERN GREAT LAKES REGION BY THURSDAY AS A DEEP  
LAYER TROUGH ENVELOPS MUCH OF THE EASTERN U.S. BY THAT TIME  
PERIOD. ALL OF THE MODEL SHOW REASONABLY GOOD AGREEMENT WITH THE  
HEIGHT FALL EVOLUTION AND SURFACE CYCLOGENESIS GOING THROUGH  
WEDNESDAY. BY THURSDAY, THERE IS SOME SPATIAL SPREAD WITH THE  
SURFACE LOW EVOLUTION AS THE 12Z NAM/GFS SOLUTIONS TAKES THE  
SURFACE LOW/ENERGY A LITTLE MORE QUICKLY NORTH ACROSS THE GREAT  
LAKES, WITH THE 00Z NON-NCEP SOLUTIONS TENDING TO KEEP LOW  
PRESSURE CONFINED MORE TO THE OH VALLEY, AND WITH A BIT BETTER  
DEFINED TRIPLE-POINT LOW OVER THE MID-ATLANTIC STATES AT THE END  
OF THE PERIOD GIVEN PLACEMENT OF STRONGER HEIGHT FALLS FOCUSING  
STILL A TAD FARTHER SOUTH. HOWEVER, AMONG THE NON-NCEP SOLUTIONS,  
THE 00Z CMC DOES APPEAR TO BE A BIT TOO WEAK WITH ITS SURFACE LOW  
REFLECTION. GIVEN THE DEPTH OF THE CLOSED LOW, A RELATIVELY SLOWER  
EVOLUTION IS PREFERRED BY THE END OF THE PERIOD, AND THIS WOULD BE  
RESPECTFUL OF THE AMPLIFYING AND TELECONNECTING RIDGE DOWNSTREAM  
OFF THE EAST COAST. THE UKMET AND ECMWF ARE RATHER WELL CLUSTERED  
AND OVERALL HAVE BETTER ENSEMBLE SUPPORT AT THIS POINT, ESPECIALLY  
FROM THE 00Z ECENS SUITE, SO WILL PREFER A NON-NCEP CONSENSUS  
WEIGHTED TOWARD THE UKMET, ECMWF AND ECENS MEAN.  
 
   
..WEAK SHORTWAVE CLIPPING THE NORTHWEST ON WEDNESDAY
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
A MODEST AND RATHER PROGRESSIVE SHORTWAVE TROUGH WILL COME IN OFF  
THE PACIFIC OCEAN AND CLIP AREAS OF THE PACIFIC NORTHWEST AND  
SOUTHERN BRITISH COLUMBIA BY LATE WEDNESDAY. A WEAK AREA OF LOW  
PRESSURE AN ATTENDANT FRONT IS EXPECTED TO ACCOMPANY THIS ENERGY.  
THE 00Z ECMWF WAS PERHAPS A TAD SLOWER THAN THE MODEL CONSENSUS,  
BUT THE MODEL DIFFERENCES ARE QUITE MODEST, SO A GENERAL MODEL  
BLEND WILL BE PREFERRED WITH THIS SYSTEM.  
 
   
..SHORTWAVE MOVING INTO THE WEST ON THURSDAY
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-GFS BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
THE MODELS BRING ANOTHER SHORTWAVE TROUGH IN OFF THE PACIFIC OCEAN  
ON THURSDAY AND IN ACROSS PORTIONS OF THE WEST. THE GUIDANCE  
REFLECTS A RELATIVELY LOW-AMPLITUDE TO THIS SYSTEM AT LEAST  
THROUGH THIS PERIOD, BUT THE GFS IS TAD STRONGER THAN THE NAM AND  
ALSO THE NON-NCEP MODELS AT THIS POINT. THE LATEST GEFS/ECENS  
MEANS ARE NOT AS ROBUST AS THE DETERMINISTIC GFS, AND SO WILL  
SUGGEST LEANING AWAY FROM THE RELATIVELY DEEPER GFS AT THIS POINT.  
 
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML  
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML  
 
ORRISON  
 

 
 
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