136  
FXUS10 KWNH 180439  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1238 AM EDT MON MAY 18 2020  
 
VALID MAY 18/0000 UTC THRU MAY 21/1200 UTC  
 
...SEE NOUS42 KWNO (ADMSDM) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
00Z MODEL EVALUATION INCLUDING PREFERENCES AND CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
TROPICAL STORM ARTHUR  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NATIONAL HURRICANE CENTER OFFICIAL TRACK  
BEST MODEL PROXY: 12Z ECMWF/00Z GFS BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
TROPICAL STORM ARTHUR, CURRENTLY WELL OFFSHORE THE SC COAST WILL  
BRUSH THE OUTER BANKS EARLY MONDAY, BEFORE TURNING NORTHEAST AWAY  
FROM THE EASTERN U.S. TUESDAY. DETERMINISTIC MODEL GUIDANCE HAS  
CONVERGED ON A SOLUTION WITH LESS SPREAD NOTED THAN 24 HOURS AGO.  
THE BEST MODEL BLEND PROXY TO THE OFFICIAL NHC TRACK IS A BLEND OF  
THE 00Z GFS AND 12Z ECMWF, CLOSE TO THE MODEL CONSENSUS, WHICH  
TAKES THE SYSTEM TO ABOUT CAPE HATTERAS AND THEN ON A  
NORTH/NORTHEAST TURN AWAY FROM THE SHORE.  
 
CONSOLIDATION OF MIDWEST AND GULF COAST SHORTWAVES INTO CUT-OFF  
UPPER LOW  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: AVERAGE  
 
A PAIR OF SHORTWAVES OVER THE CENTRAL US, ONE OVER IOWA AND THE  
OTHER ALONG THE CENTRAL GULF REGION, WILL CONSOLIDATE OVER THE  
NEXT DAY INTO A LARGE CUT-OFF LOW THAT SETTLES OVER THE TENNESSEE  
VALLEY EARLY NEXT WEEK. MODEL GUIDANCE HAS IMPROVED IN THE LAST  
COUPLE OF CYCLES AND THERE HAS BEEN SOME TIGHTENING IN THE MODEL  
SPREAD SUCH THAT FROM A MODEL MASS FIELD PERSPECTIVE, A GENERAL  
MODEL BLEND IS SUFFICIENT.  
 
DEEP UPPER LEVEL TROUGH BUILDING IN ACROSS THE WESTERN U.S.  
FOLLOWED BY SECONDARY SHORTWAVE TROUGH APPROACHING PAC NW  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND THROUGH 20.12Z, THEN ECMWF/UKMET  
BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
WITH THE AMPLIFYING UPPER LEVEL PATTERN ACROSS THE CONTINENTAL  
U.S., AN AMPLIFIED UPPER LEVEL TROUGH IS FORECAST TO BECOME  
ESTABLISHED OVER THE WEST COAST AND THEN THE INTERMOUNTAIN WEST BY  
THE MIDDLE OF THE WEEK AS A BIG UPPER LOW FROM THE NORTHEAST  
PACIFIC TRACKS SOUTHEASTWARD. THIS WILL ALSO BE IN RESPONSE TO A  
BUILDING DOWNSTREAM RIDGE AXIS ACROSS THE PLAINS AS AN OMEGA BLOCK  
PATTERN DEVELOPS. BY DAY 3, A SECONDARY SHORTWAVE TROUGH IS  
FORECAST TO DROP DOWN TOWARD THE PACIFIC NORTHWEST AND HERE, THERE  
ARE SOME MODEL DIFFERENCES. THE GFS IS ON THE FASTER SIDE OF THE  
SPREAD. A BLEND COMPOSED OF THE ECMWF/UKMET IS PREFERRED HERE FOR  
DAY 3.  
 
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML  
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML  
 
TAYLOR  
 

 
 
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