648  
FXUS10 KWNH 110504  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
104 AM EDT SUN AUG 11 2019  
 
VALID AUG 11/0000 UTC THRU AUG 14/1200 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
00Z PRELIMINARY MODEL EVALUATION WITH PREFERENCES AND CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
   
..OVERALL PATTERN ACROSS THE CONUS
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 00Z ECMWF/ECENS, 06Z GEFS  
CONFIDENCE: AVERAGE, SLIGHTLY BELOW AVERAGE DAY 3  
 
THROUGH WEDNESDAY, THE SYNOPTIC FLOW WILL TRANSITION FROM A  
MIDDLE-CONUS RIDGE, TO NEARLY ZONAL FLOW, TO A WESTERN  
RIDGE/EASTERN TROUGH BY THE END OF THE FORECAST PERIOD. WHILE THE  
GUIDANCE IS NEARLY UNIFORM IN DEVELOPING THIS EVOLUTION, THE  
TEMPORAL AND SPATIAL DEVELOPMENT VARIES CONSIDERABLY LEADING TO  
LOWERED CONFIDENCE, ESPECIALLY INTO WEDNESDAY.  
 
INITIALLY, A CLOSED LOW MOVING INTO THE NW AND A SHORTWAVE MOVING  
OVER THE SW AND ATOP THE RIDGE WILL INTERACT TO FLATTEN THE RIDGE  
INTO A MORE ZONAL PATTERN. THE NAM IS NORTH AND STRONG WITH THE  
SHORTWAVE MOVING NEAR THE CANADIAN BORDER, AND IS ALL ALONE IN  
KEEPING THE ENERGY NORTH INTO CANADA. SIMILARLY DURING THIS TIME,  
THE UKMET CONTINUES ITS SUMMER-LONG TREND OF BEING GENERALLY TOO  
STRONG WITH THE MID-LEVEL RIDGE, IN THIS CASE KEEPING THE 594DM  
HEIGHTS WELL LONGER THAN ANY OTHER GUIDANCE, AND IS GENERALLY  
ABOUT 4DM HIGHER WITH ITS HEIGHTS THAN THE REMAINING GUIDANCE.  
 
LATER IN THE FORECAST, A SHORTWAVE WILL DRIVE A COLD FRONT INTO  
THE GREAT LAKES AND INTO THE NORTHEAST, AMPLIFYING THE TROUGH IN  
THE EAST DOWNSTREAM OF THE STRENGTHENING RIDGE WHICH BACKS UP INTO  
THE SOUTHWEST ONCE AGAIN. ALONG THIS FRONT, THERE REMAINS A SIGNAL  
FOR HEAVY RAINFALL IN THE NORTHERN OH VLY AND INTO THE GREAT  
LAKES, BUT THE MODELS DIFFER CONSIDERABLY IN PLACEMENT. THE GFS  
APPEARS TOO FAR NORTH, LIKELY DUE TO WEAKER RIDGING OUT WEST  
LEADING TO MORE SUBDUED TROUGHING IN THE EAST, AND IT IS ALSO  
INCONSISTENT WITH ITSELF SHOWING A WIDE RUN-TO-RUN VARIABILITY.  
THE CMC APPEARS TO HAVE THE AXIS OF QPF ELONGATED TOO MUCH TO THE  
SOUTHEAST, A SETUP THAT WOULD BE MORE LIKELY SHOULD THE TROUGH  
BECOME NEGATIVELY TILTED, BUT IN THIS CASE REMAINS POSITIVE TO  
NEUTRAL.  
 
THAT LEAVES THE ECMWF AND THE GEFS/ECENS MEANS AS THE MOST  
REASONABLE AND MIDDLE-GROUND SCENARIO. WHILE THESE SMALL SCALE  
FEATURES ARE DIFFICULT TO DISCERN WITH HIGH CONFIDENCE, AND THE  
EVOLUTION MAY CHANGE, THE CONSISTENCY OF THE ECMWF ALONG WITH THE  
ENSEMBLE SUPPORT SUGGEST THIS BLEND SHOULD BE REASONABLE FOR THE  
ENTIRE CONUS DURING THE NEXT 3 DAYS.  
 
MODEL TRENDS AT WWW.WPC.NOAA.GOV/HTML/MODEL2.HTML  
500 MB FORECASTS AT WWW.WPC.NOAA.GOV/H5PREF/H5PREF.SHTML  
 
WEISS  
 

 
 
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