951  
FXUS10 KWNH 290653  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
252 AM EDT SUN MAR 29 2020  
 
VALID MAR 29/0000 UTC THRU APR 01/1200 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
00Z NAM/GFS EVALUATION WITH PRELIMINARY PREFERENCES AND CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
...CLOSED LOW WEAKENING FROM THE UPPER MIDWEST TO THE NORTHEAST  
THROUGH TUESDAY...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL COMPROMISE  
CONFIDENCE: ABOVE AVERAGE  
 
ONLY MINOR TIMING/THERMAL/STRENGTH DIFFERENCES REMAIN WITH THIS  
SYSTEM AS THE POWERFUL CLOSED LOW OVER THE UPPER MIDWEST ON SUNDAY  
MORNING, WEAKENS TOWARD THE NORTHEAST FOR MONDAY AND TUESDAY. AS A  
SECONDARY LOW DEVELOPS IN THE GUIDANCE SUNDAY NIGHT NEAR THE NEW  
ENGLAND COAST, MINOR PLACEMENT DIFFERENCES DEVELOP WITH PERHAPS  
THE 12Z UKMET CLOSEST TO THE COAST, BUT OVERALL DIFFERENCES IN THE  
LATEST DETERMINISTIC AND ENSEMBLE GUIDANCE ARE MINOR.  
 
...SOUTHWEST SHORTWAVE SPURRING SOUTHERN PLAINS CYCLOGENESIS EARLY  
IN THE WEEK...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 75% 12Z ECMWF, 25% 00Z NAM BLEND  
CONFIDENCE: AVERAGE  
 
SOME TIMING DIFFERENCES DEVELOP EARLY WITH THE SHORTWAVE TROUGH  
ACROSS THE SOUTHWEST. THE 00Z NAM ENDS UP FASTER THAN MOST OF THE  
GUIDANCE THROUGH MONDAY WHILE THE 12Z UKMET/CMC END UP SLOWER.  
WHILE THE SLOWER/FARTHER SOUTH TRACK OF THE 12Z UKMET/CMC'S  
SHORTWAVE CONTINUES THROUGH WEDNESDAY MORNING, THE 00Z NAM TIMING  
SLOWS MORE IN LINE WITH THE BEST ENSEMBLE CLUSTERING WHILE THE 00Z  
GFS PULLS AHEAD. THE 12Z ECMWF IS CONSIDERED THE BEST MODEL FOR  
THIS SYSTEM WITH THE 00Z NAM SECOND BEST BUT THE 00Z NAM IS A BIT  
STRONGER, COLDER AND NORTH THAN THE REMAINING GUIDANCE.  
 
CLOSED LOW AND UPPER LEVEL TROUGH APPROACHING PACIFIC NORTHWEST  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 00Z GFS/12Z ECMWF/12Z UKMET BLEND  
CONFIDENCE: AVERAGE  
 
WHILE THE 00Z GFS ENDS UP SLOWER WITH THE TIMING OF THE LEAD  
SHORTWAVE TROUGH MOVING ACROSS THE U.S./CANADIAN BORDER MONDAY  
NIGHT INTO TUESDAY, LOCATED ON THE FRONT EDGE OF A LONGWAVE TROUGH  
OVERTAKING THE NORTHWEST, WHEN THE 00Z GFS IS COMBINED WITH THE  
12Z ECMWF AND 12Z UKMET, A REASONABLE BLEND IS REACHED. THE 00Z  
NAM IS CONSIDERED TOO AMPLIFIED WITH HEIGHTS INTO THE  
INTERMOUNTAIN WEST, WHILE THE 12Z CMC IS FLATTER/WEAKER WITH THE  
OVERALL LONGWAVE TROUGH.  
 
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML  
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML  
 
OTTO  
 

 
 
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