974  
FXUS10 KWNH 290427  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1226 AM EDT FRI MAY 29 2020  
 
VALID MAY 29/0000 UTC THRU JUN 01/1200 UTC  
 
...SEE NOUS42 KWNO (ADMSDM) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
00Z MODEL EVALUATION INCLUDING INITIAL PREFERENCES AND CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
UPPER LEVEL TROUGH AND COLD FRONT ACROSS THE EASTERN U.S.  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: MODERATE-HIGH  
 
THE UPPER LEVEL LOW THAT HAD BEEN TRACKING ACROSS THE  
SOUTH-CENTRAL U.S. IS NOW IN THE PROCESS OF BECOMING ABSORBED AND  
PHASING WITH AN AMPLIFYING NORTHERN STREAM TROUGH ACROSS THE GREAT  
LAKES REGION. THIS WILL SUSTAIN THE PASSAGE OF A RATHER STRONG  
COLD FRONT BY LATE MAY STANDARDS ACROSS THE EASTERN U.S. AND  
EXITING THE EAST COAST ON SATURDAY, WITH A HIGH QUALITY AIRMASS  
SETTLING IN BEHIND IT WITH COOLER TEMPERATURES AND MUCH LOWER  
HUMIDITY. A REINFORCING SHORTWAVE WILL PIVOT AROUND THIS TROUGH  
AND FURTHER AMPLIFY THE PATTERN ACROSS THE NORTHEAST STATES, AND  
AN UPPER LEVEL RIDGE BUILDING IN BEHIND ACROSS THE PLAINS. THE  
MODELS ARE ALL IN AGREEMENT ON THE PHASING OF THE TWO DISTURBANCES  
THROUGH FRIDAY NIGHT, WITH ONLY MINOR DIFFERENCES NOTED  
THEREAFTER. THE GFS IS ONLY SLIGHTLY FASTER WITH THE PROGRESSION  
OF THE COLD FRONT ACROSS NEW ENGLAND, AND THE NAM SLIGHTLY MORE  
AMPLIFIED WITH THE UPPER TROUGH ACROSS THE MID-ATLANTIC AND  
NORTHEAST BY SUNDAY. THE DIFFERENCES ARE GENERALLY SMALL ENOUGH  
TO SUPPORT A MULTI-DETERMINISTIC MODEL BLEND.  
 
 
CLOSED UPPER LEVEL LOW THAT REACHES NORTHERN MEXICO ON FRIDAY AND  
BECOMES SLOW MOVING THROUGH THE WEEKEND  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: MODERATE-HIGH  
 
AN UPPER LEVEL TROUGH INITIALLY OVER THE SOUTHERN PLAINS, MAINLY  
EVIDENT AT THE 250MB LEVEL, WILL CONTINUE TO DROP SOUTHWARD TO  
NORTHERN MEXICO BY FRIDAY NIGHT. IT WILL LIKELY BECOME TRAPPED  
SOUTH OF THE BUILDING UPPER RIDGE OVER THE GREAT PLAINS, WITH  
LITTLE IN THE WAY OF MOVEMENT. THERE SHOULD NOT BE MUCH OF A  
SURFACE LOW REFLECTION WITH THIS TROUGH, HOWEVER. THE MODELS ARE  
IN RELATIVELY GOOD AGREEMENT ON THE HANDLING OF THIS FEATURE, AND  
THUS A GENERAL MODEL BLEND CAN BE INCORPORATED.  
 
TROUGH EVOLUTION ALONG THE WEST COAST  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND THROUGH SATURDAY AFTERNOON, THEN  
00Z NAM/GFS/12Z ECMWF BLEND  
CONFIDENCE: MODERATE  
 
A WELL DEVELOPED UPPER LEVEL LOW SITUATED NEAR 30N/125W WITH  
SUBTROPICAL ORIGINS IS FORECAST TO REACH NORTHERN CALIFORNIA BY  
MIDDAY SATURDAY, AND THEN EVOLVE INTO AN OPEN TROUGH AS IT LIFTS  
NORTHWARD ACROSS THE PACIFIC NORTHWEST AROUND THE WESTERN SIDE OF  
THE BUILDING RIDGE ACROSS THE PLAINS. A SECOND TROUGH BUILDS IN  
WEST OF CALIFORNIA BY SUNDAY EVENING AS THE FIRST TROUGH LIFTS  
NORTHWARD ACROSS WESTERN CANADA. IN TERMS OF THE MODEL EVOLUTION,  
THE 12Z UKMET IS PORTRAYING A FASTER TRACK NORTHWARD ACROSS THE  
PACIFIC NORTHWEST BY SATURDAY NIGHT, AND THE 00Z NAM AND GFS HOLD  
ONTO THE CLOSED LOW THE LONGEST BEFORE BECOMING AN OPEN WAVE.  
CONFIDENCE IS A LITTLE LOWER REGARDING THE SECOND DISTURBANCE OFF  
THE CALIFORNIA COAST, WITH THE GFS/NAM/ECMWF SHOWING A STRONGER  
500MB TROUGH COMPARED TO THE FLATTER CMC AND UKMET. THERE IS GOOD  
OVERALL ENSEMBLE SUPPORT FOR THE STRONGER SET OF SOLUTIONS HERE,  
AND A NAM/GFS/ECMWF BLEND WORKS WELL AND ALSO MAINTAINS EARLIER  
FORECAST CONTINUITY.  
 
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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