790   
FXUS10 KWNH 250647  
PMDHMD  
  
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
247 AM EDT WED MAR 25 2020  
  
VALID MAR 25/0000 UTC THRU MAR 28/1200 UTC  
  
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
  
00Z MODEL EVALUATION WITH FINAL PREFERENCES AND CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
  
EAST COAST CYCLOGENESIS THROUGH WEDNESDAY NIGHT  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: HIGH  
  
THE SURFACE LOW THAT HAS BEEN TRACKING EASTWARD ACROSS THE  
SOUTH-CENTRAL U.S. IS FORECAST TO REDEVELOP NEAR THE MID-ATLANTIC  
COASTLINE AND THEN INTENSIFY AS IT TRACKS OUT TO SEA, LIKELY  
TAKING A TRACK FARTHER OFFSHORE THAN THE RECENT NOR'EASTER THAT  
AFFECTED NEW ENGLAND MONDAY NIGHT.  THERE IS ENOUGH AGREEMENT IN  
THE GUIDANCE TO MERIT THE USE OF A MULTI-MODEL BLEND, EVEN THOUGH  
THE 12Z ECMWF IS SLIGHTLY SLOWER WITH TAKING THE LOW AWAY FROM THE  
COAST.  
  
LONGWAVE TROUGH OVER THE WESTERN U.S.  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-UKMET BLEND AFTER 12Z THURSDAY  
CONFIDENCE: MODERATE  
  
THE AMPLIFIED PATTERN OVER THE EASTERN PACIFIC WILL END UP  
PRODUCING A POSITIVELY TILTED LONGWAVE TROUGH AXIS WHICH WILL  
SLOWLY PROGRESS DOWN THE WEST COAST, AND THEN GRADUALLY MOVE  
INLAND ACROSS THE DESERT SOUTHWEST BY FRIDAY MORNING AND REACH THE  
ROCKIES BY SATURDAY MORNING.  THIS WILL SUPPORT LEE CYCLOGENESIS  
ACROSS THE WESTERN HIGH PLAINS ALONG THE EXISTING FRONTAL  
BOUNDARY.  THE MAIN DIFFERENCE HERE IS WITH THE 12Z UKMET BEING  
SLOWER WITH THE PROGRESSION OF THE TROUGH ACROSS THE INTERMOUNTAIN  
WEST, AND THUS THE EVOLVING SURFACE LOW IS WEST OF THE MODEL  
CONSENSUS BY SATURDAY MORNING.  
  
SHORTWAVE AND SURFACE COLD FRONT APPROACHING PACIFIC NORTHWEST  
SATURDAY MORNING  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 00Z GFS/00Z CMC/18Z GEFS MEAN  
CONFIDENCE: MODERATE  
  
A SHORTWAVE TROUGH ORIGINATING FROM ALASKA WILL TRACK  
SOUTHEASTWARD ACROSS THE NORTHEAST PACIFIC AND REACH THE PACIFIC  
NORTHWEST BY SATURDAY MORNING.  THIS WILL BRING THE NEXT  
SIGNIFICANT ROUND OF PRECIPITATION TO THIS REGION BY THE END OF  
THE FORECAST PERIOD.  MODEL DIFFERENCES BECOME APPARENT BY 00Z  
SATURDAY WITH THE 12Z ECMWF BECOMING MORE AMPLIFIED, AND THE UKMET  
A BIT WEAKER AND FASTER.  
  
NORTHERN STREAM SHORTWAVES CROSSING SOUTHERN CANADA THIS WEEK  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 12Z ECMWF/12Z CMC/18Z GEFS MEAN  
CONFIDENCE: MODERATE  
  
THERE WILL BE THREE SEPARATE SHORTWAVE PERTURBATIONS IN THE  
NORTHERN STREAM NEAR THE CANADIAN BORDER THAT WILL BE PIVOTING  
AROUND THE MAIN POLAR VORTEX OVER NORTHERN CANADA, WITH THE FIRST  
CROSSING THE NORTHERN GREAT LAKES ON WEDNESDAY.  THIS WILL RESULT  
IN A COLD FRONT DROPPING SOUTHWARD ACROSS THE NORTHERN PLAINS AND  
THE UPPER MIDWEST.  ALTHOUGH THERE IS GOOD MODEL AGREEMENT WITH  
THE LEAD WAVE, THERE ARE SOME TIMING AND AMPLITUDE DIFFERENCES  
WITH THE NEXT SET OF DISTURBANCES TO MOVE THROUGH.  THE GFS AND  
NAM ARE STRONGER WITH THE THIRD WAVE, AND THE UKMET IS MORE  
PROGRESSIVE.  THE ECMWF AND CMC INDICATE A SIMILAR EVOLUTION WITH  
SUPPORT FROM THE ENSEMBLE MEANS, SO A BLEND OF THESE SOLUTIONS  
WITH THE GEFS MEAN SHOULD SERVE WELL AS A STARTING POINT.  
  
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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