916  
FXUS10 KWNH 021839  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
239 PM EDT SAT MAY 2 2020  
 
VALID MAY 2/1200 UTC THRU MAY 6/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z MODEL EVALUATION INCLUDING FINAL PREFERENCES AND CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
19Z UPDATE: THE 12Z CMC HAS TRENDED TO A MORE AMPLIFIED SOLUTION  
WITH THE SHORTWAVE ACROSS THE UPPER MIDWEST AND OHIO VALLEY IN  
RESPONSE TO A STRONGER UPSTREAM RIDGE ACROSS THE ROCKIES COMPARED  
TO ITS 00Z RUN, AND SLIGHTLY STRONGER (ALONG WITH THE 12Z UKMET)  
WITH THE TROUGH OVER THE NORTHEAST ON MONDAY AND SLOWER WITH THE  
SECOND DISTURBANCE APPROACHING THE PACIFIC NORTHWEST. THERE IS  
ALSO A SLIGHTLY SLOWER TREND WITH THE 12Z UKMET OVER THE NORTHEAST  
PACIFIC AND THE RIDGE AXIS OVER THE INTERMOUNTAIN WEST, AND THE  
ECMWF TRENDED MORE AMPLIFIED. TAKING ALL OF THE MODELS INTO  
ACCOUNT, THE NAM REMAINS FASTER AND STRONGER WITH THE SHORTWAVE  
CROSSING THE NORTHERN PLAINS, AND THE CMC SLIGHTLY STRONGER WITH  
THE SURFACE LOW CROSSING THE MID-SOUTH WITH THE MORE AMPLIFIED  
TROUGH CROSSING THE OHIO VALLEY. THE GFS REMAINS SLIGHTLY FASTER  
WITH THE FRONT REACHING THE EAST COAST, AND THE UKMET IS STRONGER  
AND FARTHER SOUTH WITH THE SURFACE LOW APPROACHING THE PACIFIC  
NORTHWEST BY TUESDAY EVENING, AND MORE IN LINE ACROSS THE GREAT  
LAKES REGION COMPARED TO ITS FASTER 00Z RUN.  
 
SHORTWAVE AND SURFACE LOW TRACKING FROM GREAT LAKES TO THE  
NORTHEAST THROUGH MONDAY  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 12Z ECMWF/UKMET/NAM BLEND  
CONFIDENCE: MODERATE-HIGH  
 
A POSITIVELY TILTED SHORTWAVE TROUGH IN AN ACTIVE NORTHERN STREAM  
MID-LEVEL FLOW WILL CROSS ONTARIO AND QUEBEC THROUGH THE WEEKEND  
AND SUSTAIN A SURFACE LOW AND COLD FRONT CROSSING THE GREAT LAKES,  
OHIO VALLEY, AND THEN REACHING THE EAST COAST BY SUNDAY NIGHT.  
 
THE MODELS ARE IN EXCELLENT AGREEMENT THROUGH SUNDAY MORNING,  
AFTER WHICH THE 00Z UKMET BECOMES FASTER WITH THE UPPER LEVEL  
FEATURE. THE GFS AND ITS ENSEMBLE MEAN ARE FASTER BRINGING THE  
COLD FRONT ACROSS THE EAST COAST AND THE ARRIVAL OF HEIGHT FALLS  
ACROSS THE NORTHEAST, AND THE CMC IS NOT QUITE AS AMPLIFIED AS THE  
OTHER DETERMINISTIC GUIDANCE ALOFT. A BLEND OF THE ECMWF/NAM AND  
SOME OF THE EC MEAN WOULD WORK WELL AS A STARTING POINT AND  
MAINTAINS PREVIOUS OVERNIGHT MODEL PREFERENCE.  
 
TROUGH TRACKING FROM PACIFIC NORTHWEST TO THE GREAT LAKES THROUGH  
TUESDAY  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 12Z ECMWF/UKMET/EC MEAN BLEND  
CONFIDENCE: LOW-MODERATE  
 
SHORTWAVE ENERGY PIVOTING AROUND THE GULF OF ALASKA UPPER LEVEL  
GYRE BREAKS OFF TO THE EAST AND TRACKS NEAR THE U.S./CANADA  
BORDER, BRIEFLY BECOMING A CLOSED UPPER LOW OVER ALBERTA AND  
SASKATCHEWAN ON MONDAY BEFORE EVOLVING INTO AN OPEN WAVE AGAIN.  
THIS WILL SUSTAIN A COLD FRONT CROSSING THE INTERMOUNTAIN WEST,  
ROCKIES, AND THEN THE WESTERN HIGH PLAINS BY MONDAY.  
 
SIMILAR TO PREVIOUS RUNS, THE GFS AND TO A LESSER EXTENT THE GEFS  
MEAN ARE STILL MORE AMPLIFIED WITH THE TROUGH CROSSING THE  
NORTHERN ROCKIES AND NORTHERN PLAINS, AND THE UKMET LIKELY TOO  
WEAK WITH THE UPPER TROUGH AS IT REACHES THE GREAT LAKES BASED ON  
ENSEMBLE SPREAD. BY THE END OF THE FORECAST PERIOD, THE NAM  
BECOMES MORE AMPLIFIED AND IS A LITTLE FASTER THAN THE OTHER  
MODELS, AND ALSO LOSES ENSEMBLE SUPPORT. THIS SYSTEM CONTINUES TO  
HAVE THE MOST VARIABILITY AMONG THE GUIDANCE, THUS REDUCING  
OVERALL CONFIDENCE IN DETAILS.  
 
NEXT STORM SYSTEM APPROACHING PACIFIC NORTHWEST EARLY IN THE WEEK  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 12Z ECMWF/CMC/00Z EC MEAN BLEND  
CONFIDENCE: MODERATE  
 
THE THIRD AREA OF INTEREST WILL BE ACROSS THE NORTHEAST PACIFIC  
AND THE PACIFIC NORTHWEST BY LATE MONDAY AND INTO TUESDAY AS A  
PAIR OF SHORTWAVES PIVOT AROUND THE BROADER UPPER LEVEL LOW OVER  
THE GULF OF ALASKA, WITH A COUPLE OF RELATIVELY WEAK COLD FRONTS  
APPROACHING THE REGION.  
 
THE 00Z UKMET IS A BIT STRONGER WITH THE FIRST SHORTWAVE/FRONT  
APPROACHING THE REGION, HOWEVER IT IS STILL WITHIN THE ENSEMBLE  
SPREAD AND THE OTHER MODELS ARE RELATIVELY CLOSE IN AGREEMENT.  
WITH THE SECOND SHORTWAVE, THE NAM AND GFS ARE A LITTLE FASTER,  
THE UKMET STRONGER, AND THE GEFS MEAN SLOWER AND WELL BEHIND THE  
OPERATIONAL GFS.  
 
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML  
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML  
 
HAMRICK  
 

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab HPC Page Main Text Page