023  
FXUS10 KWNH 290644  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
244 AM EDT WED APR 29 2020  
 
VALID APR 29/0000 UTC THRU MAY 02/1200 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
00Z MODEL EVALUATION INCLUDING FINAL PREFERENCES AND CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
PLAINS TO EAST COAST STORM SYSTEM  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 00Z NAM/00Z UKMET/00Z ECMWF  
CONFIDENCE: MODERATE  
 
THE OVERALL UPPER LEVEL PATTERN OVER THE CENTRAL AND EASTERN U.S.  
WILL BECOME MORE AMPLIFIED OVER THE NEXT COUPLE OF DAYS AS AN  
UPPER LEVEL RIDGE BUILDS ACROSS THE ROCKIES AND WESTERN HIGH  
PLAINS. HEIGHT FALLS ON THE EASTERN SIDE OF THE RIDGE IS  
SUPPORTING A RAPIDLY DEVELOPING CLOSED LOW OVER THE MIDWEST AND  
DEEPENS FURTHER AS IT REACHES THE OHIO VALLEY REGION BY THURSDAY.  
AS THE MAIN SURFACE LOW OVER MICHIGAN OCCLUDES BY THURSDAY NIGHT,  
A SECONDARY SURFACE LOW FORMS OVER THE MID-ATLANTIC AND LIFTS  
NORTHWARD AS THE UPPER LEVEL TROUGH ACQUIRES SOME NEGATIVE TILT.  
 
BEYOND 00Z THURSDAY, THE 00Z GFS BECOMES A LITTLE FASTER WITH  
SHORTWAVE ENERGY PIVOTING AROUND THE UPPER LOW, AND FARTHER NORTH  
WITH THE UPPER LOW BY 00Z FRIDAY. THE CMC REMAINS A LITTLE WEAKER  
WITH THE LOW. THE UKMET, NAM, AND ECMWF ARE RELATIVELY WELL  
ALIGNED AND CLOSE TO THE ENSEMBLE MEANS, SO A BLEND OF THESE THREE  
SOLUTIONS SHOULD WORK WELL AS A STARTING POINT. THE 00Z ECMWF  
TRENDED A LITTLE BIT FARTHER TO THE EAST BY SATURDAY MORNING  
ACROSS THE NORTHEAST U.S. AND CLOSE TO THE MODEL CONSENSUS  
 
MULTIPLE SHORTWAVES AFFECTING THE PACIFIC NORTHWEST TO THE  
NORTHERN PLAINS...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 00Z ECMWF/12Z EC MEAN/00Z NAM  
CONFIDENCE: MODERATE  
 
THERE WILL BE THREE INDIVIDUAL SHORTWAVES THAT WILL AFFECT THE  
WEST COAST THROUGH THE END OF THE WEEK AND EVENTUALLY FLATTEN THE  
WESTERN U.S. RIDGE SOME IN THE PROCESS. THE LEAD SHORTWAVE  
REACHES SOUTHERN BRITISH COLUMBIA THURSDAY MORNING, FOLLOWED BY A  
FLATTER WAVE REACHING NORTHERN CALIFORNIA AND OREGON THURSDAY  
AFTERNOON. THESE EVENTUALLY PHASE INTO A STRONGER TROUGH OVER  
SOUTH-CENTRAL CANADA AND THE NORTHERN PLAINS BY FRIDAY EVENING.  
THE THIRD SHORTWAVE APPROACHES THE PACIFIC NORTHWEST COAST BY  
FRIDAY NIGHT ASSOCIATED WITH AN UPPER LOW OVER THE NORTHEAST  
PACIFIC.  
 
THE 18Z GEFS MEAN SHOWS LESS DEFINITION TO THE LEAD SHORTWAVE  
ACROSS BRITISH COLUMBIA, AND THEN THE NAM BECOME SLIGHTLY MORE  
AMPLIFIED. THERE ARE AMPLITUDE DIFFERENCE WITH THE TROUGH  
CROSSING THE PACIFIC NORTHWEST, WITH THE ECMWF AND CMC NOT AS  
STRONG AS THE UKMET/GFS/NAM, AND THE GFS IS WEAKER WITH THE  
DOWNSTREAM RIDGE AXIS. BUT SATURDAY MORNING, THE GFS IS STRONGER  
AND FARTHER SOUTH WITH THE LOW OVER MANITOBA, AND THE CMC IS NOW  
CLOSER WITH THE TIMING OF THE SURFACE FRONT ACROSS THE NORTHERN  
PLAINS COMPARED TO ITS 12Z RUN. MODEL AGREEMENT IS GOOD OVERALL  
WITH THE SYSTEM APPROACHING THE PACIFIC NORTHWEST LATER IN THE  
WEEK WITH MINOR DIFFERENCES IN THE SURFACE LOW EVOLUTION..  
 
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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