568   
FXUS10 KWNH 181843  
PMDHMD  
  
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
242 PM EDT SAT APR 18 2020  
  
VALID APR 18/1200 UTC THRU APR 22/0000 UTC  
  
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
  
12Z MODEL EVALUATION WITH FINAL PREFERENCES AND CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
  
19Z UPDATE: THE NON-NCEP GUIDANCE HAS TRENDED A LITTLE STRONGER  
WITH THE SHORTWAVE CROSSING THE DEEP SOUTH AND THIS CONTINUES WHEN  
THE SYSTEM EXITS THE EAST COAST, WITH THE 12Z NAM REMAINING ON THE  
MORE PROGRESSIVE SIDE OF THE 12Z MODEL SUITE.  THERE WAS ALSO A  
SLIGHTLY STRONGER TREND WITH THE GREAT LAKES TROUGH BY DAY 3, WITH  
THE 12Z UKMET INDICATING THE MOST AMPLIFIED SCENARIO, SO THE CMC  
REPLACES THE UKMET AS PART OF THE MODEL PREFERENCE.  OUT WEST, THE  
12Z CMC, AND TO A LESSER EXTENT THE 12Z ECMWF, TRENDED FASTER WITH  
THE UPPER LEVEL LOW OVER THE DESERT SOUTHWEST BY THE END OF THE  
FORECAST PERIOD.  HOWEVER, THE CMC STILL TRAILS THE MAJORITY OF  
THE GUIDANCE WITH THIS FEATURE.     
  
STORM INTENSIFYING OFF THE NORTHEAST COAST THIS WEEKEND  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: HIGH  
  
A POTENT SHORTWAVE TRACKING ACROSS THE MID-ATLANTIC REGION TODAY  
WILL SUPPORT AN INTENSIFYING SURFACE LOW EAST OF NEW ENGLAND AND  
SOUTH OF NOVA SCOTIA THROUGH SUNDAY.  THERE IS NOW ENOUGH MODEL  
AGREEMENT TO SUPPORT A MULTI-MODEL DETERMINISTIC BLEND.  
  
SOUTHERN STREAM SHORTWAVE WITH SURFACE LOW TRACKING ACROSS GULF  
COAST STATES  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 12Z ECMWF/12Z UKMET/12Z GFS  
CONFIDENCE: AVERAGE  
  
THE SOUTHERN STREAM SHORTWAVE EXITING THE SOUTHERN ROCKIES WILL  
GIVE WAY TO LEE CYCLOGENESIS ACROSS THE WESTERN HIGH PLAINS THIS  
EVENING, AND A WELL DEVELOPED SURFACE LOW IS PROGGED TO TRACK  
EASTWARD ACROSS THE SOUTHERN PLAINS AND DEEP SOUTH THROUGH MONDAY  
MORNING, AND THEN EXITING THE SOUTHEAST COAST.  THE 12Z NAM IS A  
BIT FASTER AND A LITTLE FARTHER NORTH COMPARED TO THE MODEL  
CONSENSUS BY SUNDAY NIGHT, AND THE 00Z CMC IS A LITTLE SLOWER WHEN  
THE SYSTEM EXITS THE EAST COAST.  OTHER THAN SOME SMALL MESOSCALE  
DIFFERENCES AMONG THE UKMET, ECMWF, AND 12Z GFS, AN INITIAL BLEND  
OF THESE MODELS WOULD SUFFICE AS A GOOD STARTING POINT IN THE  
FORECAST PROCESS.  
  
AMPLIFYING VORTEX OVER SOUTHERN CANADA WITH COLD FRONT ACROSS  
GREAT LAKES REGION  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 12Z ECMWF/12Z CMC/12Z GFS  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
  
THE LARGE SYNOPTIC SCALE TROUGH OVER CENTRAL/EASTERN CANADA AND  
THE NORTHERN TIER OF THE U.S. GETS REINFORCED WITH A STRONG  
SHORTWAVE TRACKING SOUTHWARD ACROSS MANITOBA, AND THEN EVOLVING  
INTO A COLD UPPER LOW OVER SOUTHERN ONTARIO AND QUEBEC.  THIS WILL  
SUSTAIN A COLD FRONT CROSSING THE GREAT LAKES AND OHIO VALLEY, AND  
THEN REACHING THE EAST COAST BY TUESDAY EVENING.  WHILE THERE IS  
GENERALLY GOOD MODEL AGREEMENT IN THE EVOLUTION OF THIS DEEP UPPER  
LEVEL TROUGH AND RESULTING SURFACE LOW, THE 12Z NAM BECOMES MORE  
PROGRESSIVE WITH THE COLD FRONT ACROSS THE OHIO VALLEY REGION AND  
QUICKER WITH THE ARRIVAL OF HEIGHT FALLS ACROSS SOUTHERN CANADA.   
ALTHOUGH THE UKMET IS A LITTLE STRONGER WITH THE SURFACE LOW AND  
FRONT, IT SHOULD STILL WORK AS A PART OF THE MODEL BLEND.   
  
UPPER LOW AND TROUGH REACHING THE DESERT SOUTHWEST BY TUESDAY  
MORNING  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 12Z NAM/12Z ECMWF/12Z UKMET BLEND  
CONFIDENCE: SLIGHTLY BELOW AVERAGE  
  
THE NEXT SHORT WAVE IN THE FLOW TRACKS TOWARD THE CENTRAL  
CALIFORNIA COAST AFTER MONDAY MORNING. THERE IS STILL SOME MODEL  
SPREAD CONCERNING THE TIMING OF THIS SHORT WAVE, AS IT UNDERCUTS  
MID LEVEL RIDGING ACROSS THE PACIFIC NORTHWEST.  THOUGH THERE IS A  
LOOSE CONSENSUS TAKING THE MID LEVEL SYSTEM OVER NEVADA AND  
ARIZONA BY THE END OF THE FORECAST PERIOD, EACH SOLUTION TAKES A  
SLIGHTLY DIFFERENT ROUTE GETTING THERE.  IN TERMS OF THE MODELS,  
THE 12Z GFS APPEARS MORE PROGRESSIVE WITH THE MID LEVEL SYSTEM,  
AND THE 00Z CMC IS MUCH SLOWER.  WITH THE UKMET, ECMWF, AND NAM  
BEING RELATIVELY WELL CLUSTERED THROUGH DAY 3, A BLEND OF THOSE  
MODELS SHOULD WORK WELL.  
  
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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