807  
FXUS10 KWNH 220746  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
345 AM EDT WED JUL 22 2020  
 
VALID JUL 22/0000 UTC THRU JUL 25/1200 UTC  
 
...SEE NOUS42 KWNO (ADMSDM) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
00Z PRELIMINARY MODEL EVALUATION INCLUDING PREFERENCES AND  
FORECAST CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
   
..NORTHERN TIER OF THE CONUS
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 00Z GFS, 12Z ECMWF/CMC/ECENS  
CONFIDENCE: SLIGHTLY BELOW AVERAGE  
 
BIGGEST CONCERN ACROSS THE NORTHERN TIER INVOLVES A SHORTWAVE  
MOVING FROM THE GREAT LAKES TODAY THROUGH THE  
NORTHEAST/MID-ATLANTIC FRIDAY. THIS IMPULSE DRIVES A SURFACE WAVE  
AND COLD FRONT ACROSS THE REGION, WITH A SLOWING OR STALLING OF  
THE FRONT POSSIBLE IN THE MID-ATLANTIC LATE IN THE WEEK AS IT  
BECOMES MORE PARALLEL TO THE FLOW AND MOVES INTO A STRONG  
MID-LEVEL RIDGE. THE NAM AND GEFSMEAN ARE BOTH STRONG OUTLIERS  
WITH THE AMPLITUDE OF THE TROUGH D2 INTO D3 IN THE NORTHEAST, AND  
BOTH APPEAR TO BE DUE TO DIFFERENCES IN HANDLING OF A CONVECTIVELY  
ENHANCED SHORTWAVE/MCV ON THE UPSTREAM SIDE OF THE RIDGE CAUSING  
DEEPER TROUGHING DOWNSTREAM. THE UKMET IS SHOWING ITS TYPICAL  
STRONG BIAS IN THE RIDGE, AND IS MUCH TOO HIGH WITH ITS MID-LEVEL  
HEIGHTS BEHIND THE COLD FRONT. OTHERWISE, THE MASS FIELDS ARE WELL  
AGREED UPON FOR THE MODELS COMPRISING THE PREFERENCE. HOWEVER,  
THERE ARE SOME QPF DIFFERENCES WITH THE FRONT MOVING THROUGH NEW  
ENGLAND AND THEN THE MID-ATLANTIC, MOST NOTABLY THE GFS BEING SLOW  
TO PUSH QPF SOUTHWARD. THE GFS MAY BE A BIT SLOW, BUT SOME  
UNCERTAINTY IN TIMING IS TYPICAL BEYOND 48 HOURS SO THE GFS CAN  
STILL BE INCLUDED AT THIS TIME.  
 
   
..CALIFORNIA/SOUTHWEST U.S
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 00Z NON-NCEP SUITE  
CONFIDENCE: AVERAGE  
 
A LARGE TROUGH IS PROGGED TO DEVELOP ACROSS MUCH OF THE WEST  
THROUGH THE END OF THE WEEK, INCLUDING A CLOSED MID-LEVEL LOW  
ROTATING AROUND CENTRAL CA BEFORE BECOMING ABSORBED INTO THE FLOW  
D3. THE GFS IS TOO STRONG WITH ITS OVERALL TROUGH DEPTH, AND THE  
NAM APPEARS TO BE MISHANDLING NORTHERN STREAM FEATURES MOVING  
ACROSS BRITISH COLUMBIA AND ALBERTA. THE NAM BEING TOO FAST WITH  
THE LATTER IMPACTS THE TROUGH EVOLUTION ACROSS THE WEST  
NEGATIVELY, DESPITE ONLY MODEST INTERACTION WITH THE LONGWAVE  
TROUGH DIGGING INTO THE GREAT BASIN. THE NON-NCEP MODELS ARE IN  
PRETTY GOOD AGREEMENT IN BOTH THE EVOLUTION OF THE CLOSED LOW AND  
THE PARENT LONGWAVE TROUGH, AND COMPRISE THE PREFERRED BLEND.  
 
IT IS WORTH NOTING THAT THIS ENERGY OVER THE SOUTHWEST COUPLED  
WITH AN INFLUX OF DEEPENING MONSOONAL MOISTURE FROM NORTHERN  
MEXICO AND RIO GRANDE VALLEY IS EXPECTED TO HELP DRIVE AN UPTICK  
IN THE COVERAGE AND INTENSITY OF MONSOONAL CONVECTION ACROSS THE  
FOUR CORNERS REGION THROUGH THE END OF THE WEEK.  
 
   
..EASTERLY WAVE MOVING THROUGH THE GULF OF MEXICO
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-CMC  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
A ROBUST EASTERLY WAVE WILL MOVE INTO THE CENTRAL GULF OF MEXICO  
TODAY AND THEN ADVECT SLOWLY WESTWARD TO POSSIBLY COME ONSHORE  
TEXAS FRIDAY. THE TREND OF A SUBTLY DEEPER/MORE AMPLIFIED FEATURE  
CONTINUES TONIGHT, AND WHILE THE NAM REMAINS A STRONG OUTLIER,  
THERE IS A NOTED INTENSIFICATION IN GUIDANCE FROM PRIOR RUNS, AND  
MOST GUIDANCE SHOWS A SHARP TROUGH APPROACHING TEXAS, WHILE 3 OF  
THE MODELS (NAM/CMC/ECMWF) CLOSE OFF A LOW AT 500-700MB BY 84  
HOURS. THE CMC IS THE ONLY OUTLIER IN TERMS OF POSITION, IT  
OUTRUNS THE CONSENSUS AND IS LIKELY TOO FAST. THE UKMET MAY BE A  
BIT FLATTER/WEAKER THAN CONSENSUS, WHILE THE NAM AS NOTED IS ON  
THE STRONG EDGE OF THE ENVELOPE. A GFS/ECMWF COMPROMISE COULD WORK  
WELL HERE, BUT DID NOT WANT TO COMPLETELY REMOVE THE NAM AS SOME  
LIGHT WEIGHT OF ITS DEPTH COULD PRODUCE A BETTER SOLUTION.  
 
ALSO NOTED WAS A CLOSED LOW AT 250 MB MAKING ITS WAY ALONG 30N  
OVER THE WATERS OF THE WESTERN NORTH ATLANTIC OCEAN...APPROACHING  
THE SOUTHEAST U.S. COAST BY 24/12Z IN THE GFS AND ECMWF. GIVEN  
THE FACT THE LOW HAS LITTLE REFLECTION BY 500 MB...NO PREFERENCE  
NEEDED HERE ALTHOUGH IT IS A FEATURE WORTH PROBABLY WORTH WATCHING  
IN SUBSEQUENT RUNS.  
 
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML  
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML  
 
THIS PRODUCT WILL TERMINATE AUGUST 15, 2020:  
WWW.WEATHER.GOV/MEDIA/NOTIFICATION/PDF2/SCN20-58PMDHMD_TERMINATION.  
PDF  
 
WEISS  
 

 
 
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