965   
FXUS10 KWNH 180654  
PMDHMD  
  
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
254 AM EDT SUN AUG 18 2019  
  
VALID AUG 18/0000 UTC THRU AUG 21/1200 UTC  
  
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
  
00Z MODEL EVALUATION...INCLUDING PREFERENCES AND CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
   
..OVERALL PATTERN ACROSS THE CONUS  
  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND...FL PANHANDLE/GULF COAST  
            BLEND OF THE 00Z GFS/ECMWF...REMAINDER OF CONUS  
CONFIDENCE: AVERAGE  
  
A BROAD DEEP LAYER TROUGH COVERS THE NORTHERN HALF OF THE CONUS  
WITH A FEW SMALLER SCALE SHORTWAVES CURRENTLY PROGRESSING THROUGH  
THE MIDWEST, GREAT LAKES AND NORTHEAST. THE LATEST GUIDANCE FAVORS  
THE DEEPER LAYER TROUGH ADVANCING EAST ACROSS THE MIDWEST AND  
GREAT LAKES REGION THROUGH SUNDAY, BEFORE THEN BRUSHING THE  
NORTHEAST AND RETREATING UP ACROSS SOUTHEAST CANADA ON MONDAY. IN  
GENERAL, THE 00Z NAM AGAIN APPEARS TO BE A TAD MORE AGGRESSIVE  
THAN THE GLOBAL MODELS WITH THE DETAILS OF THE SHORTWAVE IMPULSES.  
ON THE LARGER SCALE, THE GUIDANCE THOUGH APPEARS TO IN REASONABLY  
GOOD AGREEMENT WHICH INCLUDES THE LARGE SCALE TROUGH EVOLUTION  
OVER THE NORTHERN U.S. AND SOUTHERN CANADA. HOWEVER, THE HEIGHT  
FALLS WILL SEND A COLD FRONT FROM THE MIDWEST THROUGH THE  
NORTHEAST WHICH IS THEN EXPECTED TO STALL OUT ACROSS THE OHIO  
VALLEY AND MID-ATLANTIC REGION ON TUESDAY. THERE ARE SOME  
DIFFERENCES WITH RESPECT TO A COUPLE WAVES OF LOW PRESSURE RIDING  
NORTHEAST UP ALONG THE FRONT. THE 00Z NAM AND TO A GREATER EXTENT  
THE 00Z UKMET APPEAR TO BE TOO STRONG WITH THEIR WAVE ACTIVITY  
IMPACTING THE MIDWEST AND GREAT LAKES REGION.  
  
IN THE WAKE OF THE TROUGH, THE FLOW WILL AT LEAST BRIEFLY FLATTEN  
OUT AND ALLOW A LARGE 594+ DM RIDGE TO EXPAND ACROSS THE SOUTHWEST  
AND MUCH OF THE CENTRAL AND SOUTHERN PLAINS. ONCE AGAIN THOUGH,  
THE UKMET HAS THE STRONGEST RIDGE AXIS OUT OF ALL OF THE MODELS  
WHICH HAS BECOME A NOTABLE BIAS OF THE UKMET WHEN IT COMES TO  
LARGER SCALE HEIGHT RISES/RIDGING IN GENERAL. BY THE END OF THE  
SHORT RANGE PERIOD, THE LARGE SCALE FLOW WILL BECOME A BIT MORE  
AMPLIFIED ACROSS THE CONUS AS A NEW UPPER TROUGH DIGS SOUTHEAST  
ACROSS THE UPPER MIDWEST AND GREAT LAKES WHICH WILL ALLOW A NEW  
COLD FRONT TO SETTLE SOUTHEAST FROM CANADA. THE LATEST GUIDANCE IS  
IN GOOD AGREEMENT WITH THE DETAILS OF THIS OUTSIDE OF THE 00Z CMC  
WHICH TENDS TO BE A BIT DEEPER AND FARTHER SOUTH WITH THE HEIGHT  
FALLS OVER THE MIDWEST.  
  
MEANWHILE, THERE WILL BE AN UPSTREAM TROUGH APPROACHING THE  
PACIFIC NORTHWEST BY THE END OF THE PERIOD, AND THIS IS WHERE  
THERE IS MORE SUBSTANTIAL MODEL SPREAD, AS THE 00Z CMC IS SOMEWHAT  
OF A PROGRESSIVE OUTLIER. MEANWHILE, THE 00Z NAM/GFS SOLUTIONS  
BOTH HAVE THE CORE OF THEIR HEIGHT FALLS DIGGING A TAD FARTHER  
SOUTH THAN THE 00Z ECMWF SOLUTIONS WHICH ALLOWS A RATHER STRONG  
SURFACE LOW TO TRACK A TAD FARTHER SOUTH BY COMPARISON TOWARD  
COASTAL AREAS OF BRITISH COLUMBIA. THE 00Z UKMET THOUGH IS A WEAK  
OUTLIER ALOFT AND EVEN MORE SO AT THE SURFACE WITH ITS SURFACE LOW  
EVOLUTION. THESE HEIGHT FALLS IN ANY EVENT WILL DRIVE A COLD FRONT  
TO JUST OFFSHORE THE PACIFIC NORTHWEST BY EARLY WEDNESDAY.  
  
IN THE TROPICAL CONFLUENCE ZONE INVOLVING THE CENTRAL/EASTERN GULF  
COAST, SOUTHEAST AND SOUTHERN MID-ATLANTIC REGION, THERE WILL BE  
MULTIPLE WAVES OF LOW PRESSURE THAT WILL NEED TO BE CLOSELY  
MONITORED. ONE WAVE OF LOW PRESSURE JUST INLAND OVER FAR NORTHEAST  
SC WILL BE LIFTING NORTHEAST ACROSS THE NC OUTER BANKS BY EARLY  
SUNDAY AFTERNOON AND THEN WELL OUT TO SEA ON MONDAY. THE 00Z NAM  
BECOMES THE FASTEST SOLUTION WITH THIS, AND THE 00Z CMC THE  
SLOWEST. MEANWHILE, THE 00Z UKMET IS A TAD STRONGER THAN THE MODEL  
CONSENSUS. MEANWHILE, THERE IS EVIDENCE OF A NEW COMPACT AREA OF  
LOW PRESSURE SOUTH OF THE FL PANHANDLE THIS EVENING WHICH THE  
GLOBAL MODELS AND HIRES GUIDANCE TAKE GRADUALLY NORTHWARD AND  
INLAND BY MONDAY. THE GUIDANCE IS TRENDING STRONGER WITH THIS  
FEATURE AS THE 00Z NAM/UKMET AND 00Z ECMWF ALL HAVE A FAIRLY  
WELL-DEFINED LOW CENTER. THE 00Z GFS IS THE WEAKEST SOLUTION.  
  
BASED ON ALL OF THE MODEL SPREAD AND LATEST TRENDS, A BLEND OF THE  
00Z GFS AND 00Z ECMWF WILL BE PREFERRED ACROSS THE CONUS FOR THE  
MODEL MASS FIELDS, AND ACCOUNTING PRIMARILY FOR THE OUTLIER  
SOLUTIONS NOTED WITH THE NAM AND UKMET REGIONALLY. THE LATEST  
ENSEMBLE GUIDANCE STRONGLY FAVORS THE GFS/ECMWF CONSENSUS.  
HOWEVER, ONE EXCEPTION IS WITH RESPECT TO THE FL PANHANDLE LOW  
CENTER AS A GENERAL MODEL BLEND WILL BE PREFERRED WITH THIS  
FEATURE. THIS WILL SUPPORT A REASONABLY WELL-DEFINED LOW ADVANCING  
NORTH IN OFF THE GULF OF MEXICO BY MONDAY.  
  
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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