424  
FXUS10 KWNH 230649  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
248 AM EDT THU APR 23 2020  
 
VALID APR 23/0000 UTC THRU APR 26/1200 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
00Z MODEL EVALUATION WITH INITIAL PREFERENCES AND CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
OVERALL PATTERN ACROSS THE CONTINENTAL U.S.  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND THROUGH 12Z SATURDAY, THEN 00Z  
ECMWF/12Z EC MEAN BLEND FOR MOST AREAS  
CONFIDENCE: MODERATE  
 
7Z UPDATE: THE 00Z ECMWF TRENDED NORTHWARD WITH THE SURFACE LOW  
CROSSING THE OHIO VALLEY THIS WEEKEND WITH A SLIGHTLY LESS  
AMPLIFIED 500MB TROUGH ACROSS THE DEEP SOUTH COMPARED TO ITS 12Z  
RUN. THE UKMET TRENDED A LITTLE LESS AMPLIFIED WITH THE SHORTWAVE  
EXITING THE EAST COAST FRIDAY EVENING, A LITTLE STRONGER AND  
FARTHER SOUTH WITH THE NEXT STORM SYSTEM ACROSS THE MIDWEST, AND  
FASTER WITH THE PACIFIC SYSTEM APPROACHING BRITISH COLUMBIA. THE  
CMC IS NOW A LITTLE SLOWER WITH THE TROUGH CROSSING THE SOUTHERN  
U.S. ON SATURDAY. OVERALL, THERE ARE STILL SIGNIFICANT MODEL  
DIFFERENCES WITH THE WEEKEND STORM SYSTEM ACROSS THE OHIO VALLEY,  
AND GIVEN THE MODEL FLUCTUATIONS OVER THE PAST 24 HOURS, IT IS  
STILL PRUDENT TO INCORPORATE SOME OF THE EC ENSEMBLE MEAN TO  
MITIGATE THESE DIFFERENCES.  
------------------  
A SPLIT FLOW PATTERN WILL INITIALLY BE OVER THE CENTRAL AND  
EASTERN PORTIONS OF THE U.S. WITH A STRONG SOUTHERN STREAM  
SHORTWAVE TRACKING EASTWARD ACROSS THE DEEP SOUTH AND THEN EXITING  
THE EAST COAST BY FRIDAY EVENING. THIS WILL SUSTAIN A SURFACE LOW  
THAT WILL TRACK FROM THE OZARKS TO THE NORTHERN MID-ATLANTIC  
REGION, AND THE CMC BECOMES SLIGHTLY WEAKER WITH THIS DISTURBANCE  
BY FRIDAY, BUT NOT OUT OF THE REALM OF POSSIBILITY, SO A GENERAL  
MODEL BLEND SHOULD SUFFICE FOR THIS STORM SYSTEM GIVEN THE OVERALL  
DECENT MODEL AGREEMENT.  
 
THE NEXT SYSTEM ARRIVES ACROSS THE MIDWEST BY FRIDAY NIGHT AS A  
SHORTWAVE AMPLIFIES IN A NORTHWEST FLOW TYPE PATTERN. THIS WILL  
SUPPORT A SURFACE LOW AND COLD FRONT CROSSING THE CENTRAL PLAINS  
AND MIDWEST STATES, AND THEN THE LOW CROSSES THE OHIO VALLEY AND  
EVENTUALLY THE NORTHEAST STATES. THIS IS WHERE THE MODELS ARE  
DIFFERING THE MOST, WITH THE GFS BECOMING MORE AMPLIFIED BY FRIDAY  
MORNING WITH THE SHORTWAVE ACROSS THE WESTERN HIGH PLAINS, AND  
CONTINUES GOING INTO THE WEEKEND. THE NAM BECOMES SLOWER THAN THE  
MODEL CONSENSUS BY LATE FRIDAY AND THE CMC IS STRONGER WITH THE  
SOUTHERN PORTION OF THE TROUGH ACROSS THE MID-SOUTH BY SATURDAY  
MORNING. BY THE END OF THE FORECAST PERIOD, THE UKMET IS BETWEEN  
THE GEFS AND EC MEANS, AND WOULD BE A GOOD DETERMINISTIC MODEL TO  
USE ALONG WITH THE EC MEAN.  
 
ACROSS THE WESTERN U.S., AN UPPER LEVEL RIDGE AXIS BRIEFLY BUILDS  
IN ACROSS THE REGION THROUGH FRIDAY AHEAD OF THE NEXT SYSTEM  
ARRIVING FROM THE NORTH PACIFIC. THE MAIN SURFACE LOW WILL LIKELY  
IMPACT THE BRITISH COLUMBIA COAST, WITH A COLD FRONT REACHING  
WASHINGTON AND OREGON ON SATURDAY. THE GFS IS SLIGHTLY SLOWER  
WITH THE ARRIVAL OF THIS FRONT, AND THE CMC IS SLIGHTLY MORE  
AMPLIFIED. THERE IS ENOUGH AGREEMENT AMONG THE NAM, ECMWF, AND  
UKMET TO MERIT A BLEND OF THOSE MODELS.  
 
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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