248   
FXUS10 KWNH 171851  
PMDHMD  
  
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
251 PM EDT WED JUN 17 2020  
  
VALID JUN 17/1200 UTC THRU JUN 21/0000 UTC  
  
...SEE NOUS42 KWNO (ADMSDM) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
  
12Z MODEL EVALUATION INCLUDING FINAL PREFERENCES AND FORECAST  
CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
  
19Z UPDATE: THE 12Z CMC TRENDED CLOSER TO THE MODEL CONSENSUS WITH  
THE UPPER LOW LIFTING NORTHWARD ACROSS THE APPALACHIANS, WITH THE  
12Z GFS NOTED AS THE MOST PROGRESSIVE BY 00Z SUNDAY.  THERE HAS  
BEEN A SLIGHTLY MORE AMPLIFIED TREND WITH THE NON-NCEP GUIDANCE  
WITH THE TROUGH CROSSING THE CENTRAL AND NORTHERN PLAINS FRIDAY  
NIGHT AND SATURDAY, WITH THE GFS STILL INDICATING THE STRONGEST  
SOLUTION.  THE CMC STILL REMAINS WEST OF THE MODEL CONSENSUS WITH  
THE MAIN UPPER LOW ACROSS SOUTH-CENTRAL CANADA AND NOT MUCH  
DIFFERENT FROM ITS 00Z RUN.  
  
EASTERN U.S. CLOSED LOW AND COASTAL FRONT  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND THROUGH 00Z SATURDAY, THEN NON-GFS  
BLEND  
CONFIDENCE: MODERATE-HIGH  
  
THE CUT-OFF UPPER LOW THAT IS CURRENTLY PARKED OVER WESTERN NORTH  
CAROLINA IS EXPECTED TO GRADUALLY LIFT NORTH ACROSS THE  
APPALACHIANS AND EVENTUALLY REACH THE NORTHEAST U.S. BY THIS  
WEEKEND AS IT SLOWLY EVOLVES INTO AN OPEN WAVE ALOFT.  THIS IS  
SUPPORTING A SURFACE LOW OVER EASTERN NORTH CAROLINA THAT IS  
FUELING CONVECTION AND HEAVY RAIN FOR PORTIONS OF THE SOUTHEAST  
AND MID-ATLANTIC REGION.  THE MODELS ARE INDICATING VERY GOOD  
SYNOPTIC SCALE AGREEMENT ON THE PROGRESS OF THE UPPER LEVEL SYSTEM  
THROUGH FRIDAY EVENING, AFTER WHICH THE GFS AND ITS GEFS MEAN ARE  
A LITTLE QUICKER WITH THE WESTERLIES ABSORBING THE TROUGH.  IN  
CONTRAST, THE CMC TENDS TO KEEP THE CLOSED LOW INTACT AND FARTHER  
SOUTH ON SATURDAY.  AT THE SURFACE, THE 00Z UKMET IS SLIGHTLY  
STRONGER WITH THE LOW, BUT STILL WITHIN THE REALM OF  
POSSIBILITIES.  THEREFORE, BLENDING THE ECMWF/UKMET/NAM SHOULD  
WORK WELL AFTER 00Z SATURDAY.  
  
CLOSED LOW MOVING INTO THE NORTHWEST TUESDAY INTO THE NORTHERN  
HIGH PLAINS BY THURSDAY  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND THROUGH 12Z FRIDAY, THEN 12Z  
UKMET/ECMWF/EC MEAN BLEND  
CONFIDENCE: MODERATE  
  
THE UPPER LEVEL LOW OVER THE NORTHERN ROCKIES IS EXPECTED TO  
BECOME ABSORBED BY A SECOND EVOLVING UPPER LOW OVER SOUTH-CENTRAL  
CANADA BY THURSDAY MORNING.  THIS WILL SUSTAIN AN OCCLUDED SURFACE  
LOW AND A SLOW MOVING COLD FRONT ACROSS THE CENTRAL AND NORTHERN  
PLAINS THROUGH THE END OF THE WEEK.  THE TWO MAIN DIFFERENCES  
NOTED IN THE GUIDANCE IS A MORE AMPLIFIED SOLUTION WITH THE 12Z  
GFS ACROSS THE PLAINS REGARDING HEIGHT FALLS, AND THIS ALSO HOLDS  
TRUE FOR THE NAM BY SATURDAY MORNING.  THE 00Z CMC BECOMES  
DISPLACED TO THE WEST OF THE MODEL CONSENSUS BY 12Z FRIDAY WITH  
THE CLOSED LOW OVER SOUTH-CENTRAL CANADA, BUT IT DOES NOT APPEAR  
TO AFFECT QPF TOO MUCH ACROSS THE PLAINS.  THEREFORE A BLEND OF  
THE 00Z ECMWF/UKMET/EC MEAN SHOULD SUFFICE AS A STARTING POINT IN  
THE FORECAST PROCESS.  
  
TROUGH APPROACHING THE PACIFIC NORTHWEST BY FRIDAY NIGHT  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 12Z ECMWF/NAM/GFS  
CONFIDENCE: MODERATE  
  
A SHORTWAVE TROUGH PIVOTING AROUND A BROAD UPPER LEVEL GYRE OVER  
THE GULF OF ALASKA IS EXPECTED TO REACH THE OFFSHORE WATERS OF THE  
PACIFIC NORTHWEST AND VANCOUVER ISLAND BY FRIDAY EVENING,  
ACCOMPANIED BY A SLOW MOVING COLD FRONT.  THE 00Z UKMET IS SLOWEST  
IN BRINGING THIS TROUGH TOWARDS THE BRITISH COLUMBIA COAST, AND  
THIS IS MORE EVIDENT WITH ITS SURFACE LOW BEING MUCH SLOWER THAN  
THE MODEL CONSENSUS BY 12Z FRIDAY.  BY THE END OF THE FORECAST  
PERIOD SATURDAY EVENING, THE CMC IS MORE AMPLIFIED WITH THE SECOND  
SHORTWAVE TROUGH TO PIVOT TROUGH THE REGION.  THERE IS ENOUGH  
MODEL AGREEMENT AMONG THE NCEP GUIDANCE AND THE ECMWF TO MERIT A  
BLEND OF THOSE MODELS WITH AVERAGE CONFIDENCE.  
  
HAMRICK  
  
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML  
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML  
  
  
 
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