580  
FXUS10 KWNH 060656  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
255 AM EDT WED MAY 06 2020  
 
VALID MAY 06/0000 UTC THRU MAY 09/1200 UTC  
 
...SEE NOUS42 KWNO (ADMSDM) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
00Z MODEL EVALUATION INCLUDING FINAL PREFERENCES AND CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
...700 MB LOW TRACKING ACROSS THE NORTHERN MID ATLANTIC TO  
SOUTHEAST NEW ENGLAND WED EVENING AND INTO THE OFFSHORE WATERS WED  
NIGHT NIGHT-THU...  
...SURFACE LOW DEVELOPMENT OVER NORTH CAROLINA TUE NIGHT AND OFF  
THE MID ATLANTIC COAST WED/THU...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
   
..07Z UPDATE
 
 
THE 00Z ECMWF/UKMET/CMC ADJUSTED WEST TO VARYING DEGREES WITH THE  
SURFACE LOW, BUT NOT TO THE EXTENT OF THE 00Z NAM. A GENERAL MODEL  
BLEND CONTINUES TO BE PREFERRED FOR THIS SYSTEM WHICH REPRESENTS A  
SMALL NUDGE TOWARD THE COAST COMPARED TO THE PREVIOUS PREFERENCE.  
   
..PREVIOUS DISCUSSION FOLLOWS
 
 
SOME MINOR WEST-EAST DIFFERENCES EXIST WITH A SURFACE LOW TRACKING  
OFFSHORE OF THE NEW ENGLAND COAST WEDNESDAY NIGHT INTO THURSDAY  
NIGHT. THE 00Z NAM IS CLOSEST TO THE COAST WHILE THE 12Z UKMET IS  
THE FARTHEST OFFSHORE. TRENDS IN THE ENSEMBLE SCATTER LOW PLOTS  
SHOW BETTER CLUSTERING WITH THE PREFERRED MIDDLE GROUND/ENSEMBLE  
MEANS SUPPORTING A PLACEMENT BETWEEN THE WESTERN 00Z NAM AND  
EASTERN 00Z GFS/12Z ECMWF/12Z UKMET/12Z CMC. THE 12Z CMC IS  
FARTHEST FROM THE ENSEMBLE SCATTER LOW PLOT CLUSTERING, SO IT WILL  
NOT BE INCLUDED AS PART OF THE PREFERENCE.  
 
...MID-LEVEL SHORTWAVE MOVING FROM PACIFIC NORTHWEST COAST TUESDAY  
NIGHT ACROSS THE NORTHERN ROCKIES WEDNESDAY NIGHT, NORTHERN PLAINS  
THURSDAY, THEN THE MS VALLEY TO OHIO VALLEY FRIDAY...  
...COLD FRONT DROPPING SOUTHWARD THROUGH THE GREAT PLAINS ON  
THURSDAY AND LOW PRESSURE DEVELOPING ON THE FRONT IN THE OH VALLEY  
FRI, TRACKING NEAR SOUTHERN NEW ENGLAND EARLY SATURDAY...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 00Z NAM/UKMET/CMC BLEND  
CONFIDENCE: AVERAGE  
   
..07Z UPDATE
 
 
THE 00Z ECMWF/UKMET/CMC CONTINUED A TREND TO BE SLOWER, BUT THE  
00Z NAM/GFS REMAIN STRONGER. OVERALL, THE 00Z CMC REMAINS THE  
WEAKEST AND MOST PROGRESSIVE WITH THE 00Z UKMET NOW NEAR THE 00Z  
NAM. THE 00Z ECMWF MADE A SMALL ADJUSTMENT TOWARD THE PREFERENCE  
AND CAME SOUTH WITH THE SURFACE LOW TRACK RELATIVE TO ITS 12Z  
RUN...ENOUGH TO BE INCLUDED AS PART OF THE PREFERRED BLEND ALONG  
WITH THE 00Z NAM AND 00Z UKMET.  
   
..PREVIOUS DISCUSSION FOLLOWS
 
 
TIMING DIFFERENCES SHOW UP EARLY WITH THE SOUTHERN END OF A  
SHORTWAVE TROUGH WHICH IS FORECAST TO EVOLVE INTO A CLOSED LOW  
OVER MT/WY EARLY THURSDAY. THESE DIFFERENCES CONTINUE AS THE  
CLOSED LOW WEAKENS INTO AN OPEN WAVE WHICH THEN MOVES THROUGH THE  
GREAT PLAINS THURSDAY NIGHT.  
 
THE 12Z CMC IS WEAKEST AND FASTEST WITH THE MID-LEVEL SHORTWAVE  
WHILE THE 00Z NAM/GFS ARE A BIT SLOWER AND STRONGER. TRENDS IN  
BOTH THE DETERMINISTIC AND ENSEMBLE GUIDANCE HAS BEEN SLOWER AND  
STRONGER WITH THIS FEATURE SO REMOVING THE 12Z CMC IS LIKELY A  
GOOD IDEA. THE 12Z UKMET IS NEXT IN LINE WITH A SOMEWHAT WEAKER  
AND FASTER MID-LEVEL SHORTWAVE, FOLLOWED NEXT BY THE 12Z ECMWF.  
SOME BLEND OF THE 00Z NAM, 00Z GFS AND 12Z ECMWF IS PREFERRED, BUT  
WITH THE THINKING THAT THE 00Z GFS IS LIKELY TOO STRONG WITH THE  
WAVE AND 12Z ECMWF TOO WEAK.  
 
AN AVERAGE OF THE LATEST AVAILABLE ENSEMBLE MEANS IS PREFERRED FOR  
THE CLOSED LOW PLACEMENT IN SOUTHERN ONTARIO/QUEBEC AND WHEN TYING  
IT IN WITH THE FEATURE TO THE SOUTH, AND ACCOUNTING FOR ENSEMBLE  
SCATTER LOW PLOT PLACEMENT, THE 00Z NAM APPEARS TO BE THE BEST  
MIDDLE GROUND AT THIS POINT. CONFIDENCE IN THE DETAILS IS A LITTLE  
BELOW AVERAGE, BUT OVERALL, THE MODELS HAVE A DECENT HANDLE ON  
THIS SCENARIO.  
 
...MID-LEVEL SHORTWAVE AND CORRESPONDING SURFACE LOW ON FRI/SAT  
AFFECTING THE NORTHERN ROCKIES AND NORTHERN PLAINS...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 00Z GFS/ECMWF BLEND  
CONFIDENCE: SLIGHTLY BELOW AVERAGE  
   
..07Z UPDATE
 
 
THE 00Z ECMWF/UKMET/CMC ADJUSTED TOWARD THE ENSEMBLE MEANS, LESS  
SO IN THE ECMWF WHICH REMAINED RATHER SIMILAR TO ITS 12Z CYCLE.  
HOWEVER, THE ADJUSTMENT WAS RELATIVELY MINOR IN THE UKMET AND CMC,  
WITH A 00Z GFS/ECMWF CONTINUING TO REPRESENT A SOLUTION CLOSER TO  
THE BEST ENSEMBLE CLUSTERING.  
   
..PREVIOUS DISCUSSION FOLLOWS
 
 
DOWNSTREAM OF A SHARP AND ELONGATED MID-LEVEL RIDGE IN PLACE OVER  
THE WEST COAST OF NORTH AMERICA, THE NORTHERN END OF THE SHORTWAVE  
MENTIONED IN THE PREVIOUS SECTION IS FORECAST TO DROP  
SOUTHEASTWARD FROM BRITISH COLUMBIA AND ALBERTA LATE THIS WEEK.  
CONFIDENCE WITH WHERE AND WHEN THIS FEATURE DROPS SOUTHEASTWARD IS  
BELOW AVERAGE GIVEN THE COMPLEXITY OF ITS EVOLUTION. HOWEVER, THE  
ENSEMBLE MEANS PAINT A REASONABLY SIMILAR PICTURE IN THE MIDDLE OF  
THE DETERMINISTIC SPREAD. CURRENTLY, THIS MIDDLE GROUND IS BEST  
REPRESENTED BY A 00Z GFS AND 12Z ECMWF BLEND.  
 
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML  
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML  
 
OTTO  
 

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab HPC Page Main Text Page