696  
FXUS10 KWNH 271813  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
212 PM EDT SAT JUN 27 2020  
 
VALID JUN 27/1200 UTC THRU JUL 1/0000 UTC  
 
...SEE NOUS42 KWNO (ADMSDM) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z MODEL EVALUATION INCLUDING PREFERENCES AND FORECAST CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
18Z UPDATE: THE 12Z CMC TRENDED EASTWARD WITH THE TROUGH AXIS  
ACROSS THE WESTERN U.S. AND THE UPPER HIGH OVER THE GREAT LAKES  
AND ONTARIO BY THE END OF THE FORECAST PERIOD, AND CLOSER TO THE  
OTHER GUIDANCE COMPARED TO ITS 00Z RUN. IT IS THE MOST AMPLIFIED  
WITH THE DEGREE OF AMPLIFICATION OF THE UPPER TROUGH ACROSS THE  
INTERMOUNTAIN WEST, AND INLINE WITH THE MODEL CONSENSUS ACROSS THE  
EAST. THE 12Z UKMET ALSO TRENDED STRONGER ACROSS THE WESTERN U.S.  
FOR THE DAY 3 PERIOD. THE 12Z ECMWF REMAINS STRONGER WITH THE  
SECOND SHORTWAVE CROSSING THE CENTRAL AND NORTHERN PLAINS COMPARED  
TO THE OTHER GUIDANCE.  
 
CLOSED LOW OVER QUEBEC AND ACCOMPANYING SHORTWAVES  
TROUGH IMPACTING THE NORTHEAST  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-NAM BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
AN UPPER LEVEL LOW INITIALLY OVER QUEBEC WILL SUSTAIN A BROAD  
UPPER LEVEL TROUGH CENTERED OVER THE EAST COAST THROUGH THE  
WEEKEND. THE MODELS ARE IN DECENT AGREEMENT ON THE STRUCTURE OF  
THIS LOW OVER QUEBEC AND THE SOUTHWARD EXTENSION OF THE TROUGH  
ACROSS THE NORTHEAST U.S. THIS WEEKEND. ON SUNDAY, A REINFORCING  
SHORTWAVE TROUGH WILL CROSS THE GREAT LAKES AND HELP TO AMPLIFY  
THE SYNOPTIC SCALE TROUGH OVER THE NORTHEAST, AND THE MODELS  
SUPPORT THE CLOSED DROPPING SOUTH ACROSS NEW ENGLAND FOR THE  
BEGINNING OF THE WEEK. THE MAIN DIFFERENCE NOTED IN THE MODELS IS  
A SOUTHWARD DISPLACEMENT WITH THE 12Z NAM BY TUESDAY REGARDING THE  
UPPER LOW PLACEMENT, AND SIMILAR TO EARLIER NAM FORECAST RUNS, SO  
A NON-NAM BLEND WILL BE PREFERRED FOR THIS REGION.  
 
DEEP UPPER TROUGH/CLOSED LOW ACROSS THE ROCKIES AND INTERMOUNTAIN  
WEST  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF THE 12Z GFS/UKMET/ECMWF  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
A DEEP UPPER TROUGH AND ASSOCIATED CLOSED LOW IS FORECAST TO  
AMPLIFY ACROSS THE NORTHERN ROCKIES AND INTERMOUNTAIN WEST THIS  
WEEKEND AS AN UPPER-LEVEL RIDGE BUILDS ACROSS THE GULF OF ALASKA  
AND ALSO ACROSS THE MIDWEST AND GREAT LAKES REGION, SUGGESTING A  
POTENTIAL OMEGA-BLOCK PATTERN. THE MODELS REMAIN IN GOOD  
AGREEMENT ON THE EVOLUTION THROUGH SUNDAY EVENING, AFTER WHICH THE  
00Z CMC IS DISPLACED TO THE SOUTHWEST WITH THE TROUGH AXIS AND  
ALSO WITH THE DOWNSTREAM RIDGE ACROSS THE CENTRAL/NORTHERN PLAINS.  
ALTHOUGH THE GFS TRENDED A LITTLE SLOWER IN LIFTING THE TROUGH  
TOWARDS THE NORTHEAST BY THE END OF THE FORECAST PERIOD COMPARED  
TO ITS 6Z AND 00Z RUNS, IT STILL REMAINS A BIT MORE PROGRESSIVE  
THAN THE MODEL CONSENSUS FOR THE DAY 3 PERIOD. TAKING THESE  
FACTORS INTO ACCOUNT, A ECMWF/UKMET/NAM BLEND SHOULD SERVE WELL AS  
A STARTING POINT IN THE FORECAST PROCESS.  
 
SHORTWAVES LIFTING NORTHEAST OVER THE PLAINS/MIDWEST  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF THE 12Z UKMET/GEFS MEAN/00Z ECENS MEAN  
CONFIDENCE: AVERAGE  
 
AHEAD OF THE DEEP WESTERN U.S. TROUGH/CLOSED LOW WILL BE A PAIR OF  
SHORTWAVE TROUGHS THAT EJECT NORTHEAST OUT OF THE SOUTHWEST AND  
ACROSS THE PLAINS AND MIDWEST. SIMILAR TO EARLIER RUNS, THE 12Z  
NAM CONTINUES TO SUGGEST A STRONGER SOLUTION WITH THE FIRST  
SHORTWAVE AS IT TRACKS TOWARDS THE NORTHEAST FROM THE CENTRAL  
PLAINS TO THE UPPER MIDWEST THROUGH SUNDAY, IN CONTRAST TO THE  
GLOBAL MODELS BEING LESS AMPLIFIED. THE SECOND SHORTWAVE HAS SOME  
MODEL SPREAD NOTED AS THE 00Z ECMWF/ECENS MEAN SUPPORT A SOMEWHAT  
STRONGER SOLUTION VERSUS THE REMAINING GUIDANCE, WHICH IS A LITTLE  
LESS AMPLIFIED. FOR NOW, A BLEND OF THE ENSEMBLE MEANS AND THE  
12Z UKMET WILL BE PREFERRED WITH BOTH SHORTWAVE IMPULSES.  
 
REMNANT ENERGY ACROSS THE LOWER MS VALLEY  
WEAKNESS LINGERING OVER TEXAS  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
THE MODEL SUPPORT A GRADUAL BUILDING OF THE SUBTROPICAL RIDGE THIS  
WEEKEND ACROSS THE FL PENINSULA AND ADJACENT AREAS OF THE GULF  
COAST STATES. SOME OF THE WEAK SHORTWAVE ENERGY LINGERING OVER  
THE LOWER MISSISSIPPI VALLEY SHOULD SHEAR OUT OVER TOP OF THE  
RIDGE THROUGH SATURDAY. HOWEVER, THERE WILL STILL BE A BROAD  
MID-LEVEL WEAKNESS/TROUGH LINGERING OVER TEXAS WHICH SHOULD TEND  
TO RETROGRADE WESTWARD THROUGH SATURDAY, BEFORE THEN LIFTING NORTH  
ACROSS THE SOUTHERN AND CENTRAL PLAINS AHEAD OF THE DEEP WESTERN  
U.S. TROUGH/CLOSED LOW. A GENERAL MODEL BLEND WILL AGAIN BE  
PREFERRED WITH THE WEAK TROUGH OVER TEXAS.  
 
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML  
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML  
 
HAMRICK  
 

 
 
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