566  
FXUS10 KWNH 210648  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
247 AM EDT SAT SEP 21 2019  
 
VALID SEP 21/0000 UTC THRU SEP 24/1200 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
00Z MODEL EVALUATION WITH PREFERENCES AND FORECAST CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
   
..SYNOPSIS
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
THE SYNOPTIC PATTERN WILL FEATURE A RATHER STRONG DEEP LAYER RIDGE  
ACROSS A LARGE PORTION OF THE EASTERN U.S. THIS WEEKEND, AS A PAIR  
OF FAIRLY ROBUST NORTHERN STREAM TROUGHS TRAVERSE THE WESTERN AND  
CENTRAL U.S. THE FIRST TROUGH WILL ADVANCE EAST ACROSS THE  
CENTRAL/NORTHERN PLAINS AND UPPER MIDWEST SATURDAY AND SUNDAY  
ALONG WITH AN ATTENDANT COLD FRONT AND A MULTIPLE WAVES OF LOW  
PRESSURE RIDING UP ALONG IT. THIS ENERGY WILL BREAK DOWN THE RIDGE  
OVER THE EAST BY LATER SUNDAY AND WILL ALLOW A COLD FRONT TO  
ARRIVE ACROSS THE OH VALLEY AND LOWER GREAT LAKES REGION BY  
MONDAY. THE HEIGHT FALLS ARE EXPECTED TO SHARPEN A BIT OVER THE  
NORTHEAST BY TUESDAY, AND THERE IS SUPPORT FOR A SOMEWHAT STRONGER  
SURFACE LOW TO DEVELOP OVER THE INTERIOR OF NORTHERN NEW ENGLAND  
AS THE COLD FRONT PUSHES OFF THE EAST COAST. MEANWHILE, A SECOND  
UPSTREAM TROUGH WILL CROSS THE WEST COAST AND MOVE INTO THE GREAT  
BASIN BY MONDAY BEFORE THEN CUTTING OFF FROM THE WESTERLIES AND  
DROPPING INTO THE SOUTHWEST ON TUESDAY. THIS UPPER TROUGH WILL BE  
A KEY PLAYER IN ALSO STEERING THE MOISTURE AND ENERGY ASSOCIATED  
WITH HURRICANE LORENA UP ACROSS AREAS OF NORTHWEST MEXICO AND INTO  
PARTS OF THE FOUR CORNERS REGION ON MONDAY AND TUESDAY.  
 
   
..DEEP TROUGH CROSSING THE PLAINS/MIDWEST THIS WEEKEND
 
   
..ENERGY CLOSING OFF OVER THE NORTHEAST EARLY NEXT WEEK
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND...THROUGH 60 HOURS  
NON-GFS BLEND...AFTER 60 HOURS  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
MODEL DIFFERENCES WITH THE FIRST TROUGH ARE RATHER SMALL THROUGH  
MOST OF THE WEEKEND AS THE ENERGY CROSSES THE INTERMOUNTAIN WEST  
AND ADVANCES ACROSS THE PLAINS AND MIDWEST, BUT BY LATER MONDAY  
AND TUESDAY AS THE ENERGY CROSSES THE GREAT LAKES AND MOVES INTO  
THE NORTHEAST, THE 00Z GFS BECOMES A BIT MORE PROGRESSIVE THAN THE  
REMAINING GUIDANCE. THE 00Z NON-NCEP GUIDANCE IS NOW ALL VERY WELL  
CLUSTERED AND CLOSE TO THAT OF THE 00Z NAM. THE 00Z GEFS MEAN IS A  
TAD MORE PROGRESSIVE THAN THE NON-GFS SUITE OF MODELS TOWARD THE  
END OF THE PERIOD, BUT NOT AS PROGRESSIVE AS THE DETERMINISTIC  
GFS, WHICH SUGGESTS THE GFS IS A BIT OF AN OUTLIER AT LEAST BY THE  
END OF THE PERIOD. WILL RECOMMEND A GENERAL MODEL BLEND THROUGH  
ABOUT 60 HOURS, AND THEN A NON-GFS BLEND THEREAFTER.  
 
   
..UPPER TROUGH DIGGING INTO THE WEST BY MONDAY
 
   
..CLOSED LOW EVOLUTION OVER THE SOUTHWEST BY TUESDAY
 
   
..MOISTURE/ENERGY ASSOCIATED WITH HURRICANE LORENA
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF THE 00Z NAM/GFS AND 00Z UKMET  
CONFIDENCE: AVERAGE...BECOMING BELOW AVERAGE BY MON/TUES  
 
REGARDING THE SECOND TROUGH, THE MODEL GUIDANCE IS WELL CLUSTERED  
AND IN GOOD AGREEMENT WITH RESPECT TO TIMING AND DEPTH AS THE  
SYSTEM ARRIVES ON MONDAY IN ACROSS THE INTERMOUNTAIN WEST.  
HOWEVER, BY TUESDAY AS THE ENERGY CUTS OFF AND DROPS SOUTH INTO  
THE SOUTHWEST, THE 00Z ECMWF IS POSITIONED WEST OF THE 00Z NAM/GFS  
AND 00Z UKMET SOLUTIONS WHICH ARE NOW PRETTY WELL CLUSTERED. THE  
00Z CMC IS NOW THE FARTHEST EAST SOLUTION BY THE END OF THE  
PERIOD. THE SPREAD IN THE GUIDANCE DOES STILL PLAY A ROLE IN HOW  
THE MOISTURE AND ENERGY ASSOCIATED WITH HURRICANE LORENA EVOLVES  
WHICH IS EXPECTED TO LIFT NORTH THROUGH THE GULF OF CA AND ACROSS  
ADJACENT AREAS OF NORTHWEST MEXICO THROUGH THE PERIOD. THE 00Z  
GEFS MEAN IS FARTHEST EAST WITH ITS TROUGH/CLOSED LOW AT THE END  
OF THE PERIOD AND IS EVEN A LITTLE EAST OF THE CMC SOLUTION. THE  
12Z ECENS MEAN TENDS TO SUPPORT THE MAJORITY CLUSTER OF SOLUTIONS,  
BUT IT DOES SUGGEST THE 00Z ECMWF MAY BE A TAD TOO FAR WEST. BASED  
ON THE LATEST CLUSTERING OF SOLUTIONS, A BLEND OF THE 00Z NAM/GFS  
AND 00Z UKMET WILL BE PREFERRED. CONFIDENCE BECOMES A BIT LIMITED  
LATE IN THE PERIOD THOUGH BASED ON THE RELATIVELY LARGE ENSEMBLE  
SPREAD SEEN WITH THE HEIGHT FALL DETAILS.  
 
MODEL TRENDS AT WWW.WPC.NOAA.GOV/HTML/MODEL2.HTML  
500 MB FORECASTS AT WWW.WPC.NOAA.GOV/H5PREF/H5PREF.SHTML  
 
ORRISON  
 

 
 
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