219  
FXUS10 KWNH 150428  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1227 AM EDT FRI MAY 15 2020  
 
VALID MAY 15/0000 UTC THRU MAY 18/1200 UTC  
 
...SEE NOUS42 KWNO (ADMSDM) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
00Z MODEL EVALUATION INCLUDING PREFERENCES AND CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
...CLOSED LOW OVER THE NORTHERN PLAINS AND UPPER GREAT LAKES  
TONIGHT...CROSSING NORTHERN NEW ENGLAND FRI...  
...SURFACE LOW MOVING FROM THE NORTHERN PLAINS TONIGHT INTO  
NORTHERN NEW ENGLAND FRI...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 00Z GFS, 12Z ECMWF, 12Z CMC BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
SHORTWAVE ENERGY CURRENTLY ALONG THE MINNESOTA/CANADIAN BORDER  
WILL QUICKLY SKIRT EASTWARD ACROSS THE NORTHERN GREAT LAKES AND  
INTO THE NORTHEAST BY SATURDAY. THE MODEL GUIDANCE HAS CLUSTERED  
FAIRLY WELL ON A SOLUTION EXCEPT FOR SOME TIMING ISSUES ON DAY 3  
BETWEEN THE SLOWER UKMET AND FASTER NAM 500 SHORTWAVE TIMING.  
THESE DIFFERENCES ARE ALSO MANIFESTED AT THE SURFACE WHERE THE NAM  
IS A BIT TOO DEEP AND ON THE NORTHERN END OF THE MODEL GUIDANCE  
WHILE THE UKMET IS SLOWER AND TO THE SOUTHWEST. FOR THESE REASONS,  
THE WPC PREFERENCE IS FOR A BLEND OF THE OTHER DETERMINISTIC  
GUIDANCE (00Z GFS, 12Z ECMWF, AND 12Z CMC).  
 
   
...CLOSED MID LEVEL LOW OFF THE PACIFIC NORTHWEST TODAY
 
MOVING  
TO THE NORTHERN PLAINS SAT AND  
THE UPPER GREAT LAKES SUN...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
A LARGE CLOSED MID/UPPER LEVEL LOW IS FORECAST TO MOVE FROM THE  
EASTERN PACIFIC TOWARD THE PACIFIC NORTHWEST COAST THROUGH THE  
PERIOD. WITH THE HIGHLY AMPLIFIED PATTERN, THE MODEL GUIDANCE  
SHOWS REASONABLE AGREEMENT WITH ONLY SOME MINOR DIFFERENCES AT 500  
MB ON DAY 3 NOTED (FASTER GFS BIAS). AT THE SURFACE A LOW WILL  
APPROACH THE COAST AND THEN WASH OUT BY DAY 3 AS THE OVERALL  
SYSTEM SLOWS/STALLS OFF THE COAST. THE MODEL GUIDANCE IS NOW  
FAIRLY CLUSTERED AND A GENERAL MODEL BLEND SHOULD SUFFICE THROUGH  
THE PERIOD.  
 
...DEVELOPING LONG WAVE TROUGH MOVING FROM NORTHERN MEXICO INTO  
CENTRAL TX SAT...THEN INTO  
THE LOWER MS VALLEY SUN...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-12Z NAM BLEND  
CONFIDENCE: AVERAGE  
 
WEAK SHORTWAVE TROUGHING WILL MOVE ACROSS THE SOUTHERN PLAINS THIS  
WEEKEND AND GRADUALLY TAKES THE SLOW MOVING MID LEVEL SLOW INTO  
THE LOWER MS VALLEY BY LATE IN THE WEEKEND. THE 00Z NAM IS THE  
LEAST FAVORED DETERMINISTIC MODEL, AS IT IS CONSIDERABLY SLOWER  
WITH THE WAVE MOVING INTO THE LOWER MS BY SUNDAY COMPARED TO THE  
REST OF THE GUIDANCE. THE 12Z UKMET DOES REMAIN ON THE SLOWER SIDE  
TOO BUT HAS TRENDED TOWARD THE REST OF THE GUIDANCE  
(CMC/ECMWF/GFS) IS PICKING UP THE SYSTEM EASTWARD. AS SUCH, WILL  
CONTINUE TO FAVOR A NON-00Z NAM BLEND.  
 
   
..LOW PRESSURE DEVELOPING NEAR THE BAHAMAS FRIDAY
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 12Z GFS/12Z ECMWF/00Z ECMWF MEAN BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE\  
 
WEAK AREA OF LOW PRESSURE IS FORECAST TO DEVELOP OFF THE SOUTHERN  
FLORIDA COAST FRIDAY AND GRADUALLY MOVE TOWARD THE BAHAMAS FRIDAY  
NIGHT BEFORE TURNING NORTHWARD THIS WEEKEND. FORECAST GUIDANCE  
AGREEMENT AND CONFIDENCE REMAINS AVERAGE AT BEST AND BEGINS TO  
DIVERGE BEYOND 48 HOURS. THE 12Z UKMET WAS A CLEAR OUTLIER, WELL  
EAST OF THE MODEL CONSENSUS AND MOST OF THE DETERMINISTIC  
GUIDANCE. MEANWHILE, THE 00Z NAM IS ON THE WESTERN SIDE OF THE  
MODEL SPREAD ENVELOPE AS WELL AS A BIT DEEPER WITH THE LOW AS IT  
TRACKS TO NEAR THE NC COAST BY 84 HOURS. THE REST OF THE  
DETERMINISTIC GUIDANCE (12Z CMC, 12Z ECMWF, AND 00Z GFS) ARE  
REASONABLY CLUSTERED THROUGH 3 DAYS AS A MIDDLE GROUND CONSENSUS.  
THERE IS ALSO PRETTY GOOD AGREEMENT WITH THE GEFS AND ECENS MEANS.  
AS SUCH, THE FAVORED BLEND INCORPORATES THE 00Z GFS, 12Z ECMWF,  
18Z GEFS, AND 12Z ECENS. FOR MORE INFORMATION ON THIS SYSTEM AND  
POTENTIAL DEVELOPMENT, SEE THE LATEST FROM THE NATIONAL HURRICANE  
CENTER.  
 
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML  
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML  
 
TAYLOR  
 

 
 
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