104  
FXUS10 KWNH 090647  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
246 AM EDT THU APR 09 2020  
 
VALID APR 09/0000 UTC THRU APR 12/1200 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
00Z MODEL EVALUATION INCLUDING FINAL PREFERENCES AND FORECAST  
CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
CLOSED LOW OVER NORTHEAST; DEEPENING SURFACE LOW OFF NEW ENGLAND  
COAST  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
07Z UPDATE: NO SIGNIFICANT CHANGES WITH THE REST OF THE 00Z  
GUIDANCE TO WARRANT A CHANGE FROM THE MODEL BLEND PREFERENCE.  
 
---PREVIOUS DISCUSSION---  
ANOMALOUS CLOSED LOW CURRENTLY OVER NORTHERN GREAT LAKES WILL  
DEEPEN AND TAKE A NEGATIVE TILT AS IT APPROACHES THE NORTHEAST  
LATER TODAY WHILE AT THE SURFACE, LOW PRESSURE WILL MOVE TOWARD  
THE EASTERN GREAT LAKES. A SECONDARY LOW WILL DEVELOP ALONG THE  
I-95 CORRIDOR AND DEEPEN ALONG COASTAL MAINE. OVERALL, THE MASS  
FIELDS HAVE COME INTO VERY GOOD AGREEMENT WITH THE EVOLUTION OF  
THIS SYSTEM OVER THE NEXT 24-36 HOURS SUCH THAT A GENERAL MODEL  
BLEND SHOULD SUFFICE.  
 
SLOW MOVING CLOSED LOW ACROSS THE SOUTHWEST  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: ECMWF/ECENS/UKMET/CMC BLEND  
CONFIDENCE: AVERAGE  
 
07Z UPDATE: THE 00Z ECMWF/CMC/UKMET STILL ADVERTISE A SLOWER  
SOLUTION, PUTTING THE GFS AND NAM SOLIDLY AS FAST OUTLIERS. THE  
CMC/UKMET APPEAR MORE USABLE, SO WILL GO AHEAD AND UPDATE THE  
BLEND TO INCLUDE THE 00Z CMC/UKMET.  
 
---PREVIOUS DISCUSSION---  
LARGE, SLOW MOVING CUT-OFF SOUTHERN STREAM CLOSED LOW OVER  
SOUTHERN CALIFORNIA IS EXPECTED TO GRADUALLY MOVE EASTWARD AS IT  
INTERACTS WITH APPROACHING NORTHERN STREAM ENERGY ON DAY 3. UNTIL  
THEN, MOVEMENT WILL BE SLOW AND OVER THE LAST SEVERAL MODEL  
CYCLES, THE ECMWF HAS PROVEN TO BE MORE CONSISTENT. BOTH THE 18Z  
GEFS AND 00Z GFS ARE FAST OUTLIERS WITH THE EJECTION OF THE  
FEATURE INTO THE SOUTHERN PLAINS ON DAY 3, THOUGH IT IS WORTH  
NOTING THAT THE 00Z GFS DID TREND SLOWER, AND IS NOW SLOWER THAN  
THE 18Z GEFS MEAN, SO PERHAPS LATER RUNS OF THE GFS WILL CATCH ON  
TO THE TREND. THE UKMET IS ALSO LESS FAVORED AS IT HAS ITS UPPER  
LOW TOO FAR TO THE SOUTHWEST, AND DIGS FURTHER SOUTH INTO THE BAJA  
REGION. OTHERWISE, A BLEND OF THE ECMWF/ECENS MEAN WITH SOME  
INCLUSION OF THE CMC SEEMS LIKE A GOOD APPROACH FOR THIS SYSTEM  
MASS FIELDS.  
 
UPPER LEVEL TROUGH AND COLD FRONT REACHING THE NORTHWEST BY END OF  
THE WEEK  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: CMC/ECMWF/ECENS MEAN  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
SHORTWAVE ENERGY ALONG THE SOUTHERN COAST OF ALASKA WILL PROGRESS  
EASTWARD TO THE YUKON TERRITORY, AND WITH THE ACCELERATING/EXITING  
JET, THE UPSTREAM RIDGE WILL BREAK DOWN AND ALLOW FOR GREATER  
PROPAGATION EAST AND THEN SOUTHWARD ACROSS SOUTHWESTERN CANADA.  
THE HEIGHT-FALLS WILL OVERSPREAD THE LEE OF THE CANADIAN ROCKIES  
AND THEN NORTHERN HIGH PLAINS, AND SUPPORT A SURFACE COLD FRONT TO  
DROP SOUTHWARD ACROSS MONTANA AND THE DAKOTAS. SOME TIMING  
DIFFERENCES ARE NOTED IN THE LATEST GUIDANCE, WHERE THE GFS/NAM  
AND THE UKMET TO SOME DEGREE WHERE A BIT FASTER THAN THE 12Z  
ECMWF/CMC. A LOOK AT THE LATEST ENSEMBLE MEANS, THE SLOWER TREND  
WOULD BE FAVORED AND THE GFS/NAM ARE LIKELY TOO FAST WITH ITS  
PROGRESSION OF THE COLD FRONT ACROSS THE NORTHERN PLAINS.  
 
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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