582  
FXUS10 KWNH 190710  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
309 AM EDT TUE MAY 19 2020  
 
VALID MAY 19/0000 UTC THRU MAY 22/1200 UTC  
 
...SEE NOUS42 KWNO (ADMSDM) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
00Z MODEL EVALUATION INCLUDING PREFERENCES AND CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
07Z UPDATE: NO SIGNIFICANT CHANGES NOTED WITH THE REST OF THE 00Z  
GUIDANCE NOW AVAILABLE.  
 
TROPICAL STORM ARTHUR  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NATIONAL HURRICANE CENTER OFFICIAL TRACK  
BEST MODEL PROXY: 00Z GFS, 12Z ECMWF BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
T.S. ARTHUR CONTINUES TO PULL AWAY FROM THE EAST COAST WITH ITS  
NORTH-NORTHEAST MOTION. OVER THE NEXT 24 HOURS, THE SYSTEM WILL  
GRADUALLY TURN TO THE EAST. THE LATEST GUIDANCE STILL EXHIBITS  
SOME DIFFERENCES, WITH THE 12Z CMC CONSIDERABLY SLOW WHILE THE 12Z  
UKMET IS ON THE FASTER SIDE OF THE MODEL SPREAD. THE NAM/GFS DO  
TREND SLOWER THAN THE ECMWF BEYOND 24 HOURS BUT THE BEST MODEL  
BLEND PROXY TO THE OFFICIAL NHC TRACK IS A COMPROMISE BLEND OF THE  
GFS/ECMWF. PLEASE CONSULT THE LATEST NHC FORECAST ADVISORIES FOR  
MORE INFORMATION ON ARTHUR.  
 
CUT-OFF LOW OVER LOWER OHIO AND TN RIVER VALLEYS  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND...THROUGH 60 HOURS  
ECMWF/UKMET/GEFS BLEND THEREAFTER  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
LARGE ANOMALOUS CLOSED UPPER LEVEL WILL FURTHER REMOVE ITSELF FROM  
THE NORTHERN STREAM FLOW AND BECOME CUT-OFF IN THE NEXT 12-24  
HOURS OVER THE LOWER OHIO VALLEY, EVENTUALLY SETTLING OVER THE TN  
RIVER VALLEY BY DAY 2/3. THROUGH 60 HOURS, THE MODEL AGREEMENT IS  
QUITE HIGH AND THE LATEST GUIDANCE SHOWS VERY GOOD PREDICTABILITY  
AND CONSISTENCY FROM THE PAST SEVERAL RUNS. BEYOND 60 HOURS, THE  
CMC BECOMES AN OUTLIER AND UNUSABLE AS IT DRIFTS THE LOW TOO FAR  
TO THE EAST AND TOO FAST. THE 00Z GFS SHOWS AN WEAKENING/OPENING  
UP WAVE EARLIER THAN THE REST OF THE MODELS AND ALLOW THE FEATURE  
TO LIFT NORTH TOWARD THE GREAT LAKES BY THE END OF THE PERIOD,  
WHICH APPEARS TO BE TOO FAST LOOKING AT THE ENSEMBLE. THE  
ECMWF/UKMET SHOW BETTER RUN TO RUN CONSISTENCY AND ARE BETTER  
ALIGNED WITH THE ENSEMBLE MEANS (INCLUDING THE GEFS) SUCH THAT  
WILL BE THE RECOMMENDED MODEL BLEND PREFERENCE AT THIS TIME.  
 
DEEP UPPER TROUGH ADVANCING ACROSS THE WESTERN U.S. BY TUESDAY  
SECONDARY UPPER TROUGH OVER THE PACIFIC NORTHWEST BY THURSDAY  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND...THROUGH 60 HOURS  
GFS/ECMWF BLEND...AFTER 60 HOURS  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
WITH THE AMPLIFYING UPPER-LEVEL PATTERN ACROSS THE CONTINENTAL  
U.S., A LARGE UPPER-LEVEL TROUGH AND ASSOCIATED CLOSED LOW IS  
FORECAST TO CROSS THE WEST COAST TODAY AND ADVANCE INLAND ACROSS  
THE INTERMOUNTAIN WEST BY TUESDAY. GIVEN THE LARGER SCALE OMEGA  
BLOCK PATTERN EVOLVING ACROSS THE U.S., THIS UPPER LOW/TROUGH  
ACROSS THE WEST WILL SLOW DOWN AND SHOULD REMAIN IN PLACE GOING  
THROUGH WEDNESDAY. HOWEVER, THE ARRIVAL OF ANOTHER STRONG UPPER  
TROUGH AND ASSOCIATED CLOSED LOW FROM THE GULF OF ALASKA AND  
CROSSING THE PACIFIC NORTHWEST BY THURSDAY SHOULD ACT TO KICK OUT  
THE ENERGY OVER THE INTERMOUNTAIN WEST AND LARGELY BACK INTO  
SOUTHWEST CANADA, ALTHOUGH THERE WILL BE A TRAILING TROUGH AXIS  
THAT ADVANCES EAST ACROSS THE ROCKIES AND THE NORTHERN HIGH PLAINS  
BY THE END OF THE PERIOD. THROUGH 60 HOURS, THE MODEL GUIDANCE  
SHOWS PRETTY GOOD PREDICTABILITY BUT BEYOND THAT, WITH THE  
APPROACH OF THE STRONGER SECONDARY SYSTEM, HOW QUICKLY THIS ENERGY  
EJECTS EASTWARD IS DIFFERENT IN THE VARIOUS DETERMINISTIC  
SOLUTIONS. THE NAM AND CMC APPEAR TO BE TOO FAST AND TOO DEEP, SO  
FOR NOW, WILL PREFER A ECMWF/GFS BLEND AFTER 60 HOURS WHICH ALIGNS  
BETTER WITH THE ENSEMBLE MEANS.  
 
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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