570  
FXUS10 KWNH 241643  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1242 PM EDT TUE OCT 24 2017  
 
VALID OCT 24/1200 UTC THRU OCT 28/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z MODEL EVALUATION...WITH PRELIMINARY PREFERENCES AND CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
   
..DEEP OCCLUDING CYCLONE OVER THE GREAT LAKES REGION
 
 
...CLIPPER SHORTWAVE DIGGING FROM THE CANADIAN PRAIRIES TO THE  
OHIO RIVER VALLEY BY WEDNESDAY NIGHT...   
..EVENTUAL NEGATIVE TILT TROUGH EJECTING THROUGH THE NORTHEAST
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND 60 PERCENT 00Z ECMWF  
40 PERCENT 12Z GFS  
CONFIDENCE: ABOVE AVERAGE  
 
MODEL SPREAD HAS CONTINUED TO NARROW WITH THESE SYSTEMS OVER THE  
PAST SEVERAL MODEL CYCLES. THE 00Z CYCLE FROM YESTERDAY EVENING  
WAS IN FAIRLY GOOD AGREEMENT...AND THE 12Z GFS HAS TRENDED CLOSER  
TO THE 00Z ECMWF. THE EUROPEAN MODEL HAS SHOWN THE GREATEST  
RUN-TO-RUN CONSISTENCY OF THE OPERATIONAL MODELS IN HOW IT HANDLES  
THE DIGGING SHORTWAVE ON THE BACKSIDE OF THE CURRENT TROUGH...AND  
THE EVENTUAL EJECTION OF THE TROUGH THROUGH THE NORTHEAST. THE 00Z  
CMC IS VERY CLOSE TO THE ECMWF SOLUTION ALOFT...BUT SHOWS HIGHER  
SURFACE PRESSURES THROUGH THE EASTERN CONUS. GIVEN THAT THIS WOULD  
BE OCCURRING IN THE PRESENCE OF A DIGGING SHORTWAVE THE PREFERENCE  
WOULD TEND TO BE FOR LOWER PRESSURES ANYWAY...AND THIS IS WHERE  
THE MODEL CONSENSUS LIES. THE 00Z UKMET AND 12Z NAM ARE CLOSER TO  
THE EXTREMES OF CURRENT MODEL SPREAD IN THE TIMING OF THE TROUGH  
AS IT EJECTS NORTHEAST...WITH THE UKMET ON THE FAST (AND LOWER  
AMPLITUDE) END OF GUIDANCE...AND THE NAM ON THE SLOW END (WITH THE  
SHORTWAVE DIGGING MORE INITIALLY). PREFER A SOLUTION CLOSER TO THE  
MORE CONSISTENT OPERATIONAL ECMWF...AS THE TREND HAS BEEN IN THAT  
DIRECTION. THE OVERALL PREFERENCE WILL BE FOR A BLEND OF THE 00Z  
ECMWF AND 12Z GFS...WEIGHTED SLIGHTLY TOWARD THE ECMWF.  
 
   
..SHORTWAVE TROUGH REACHING BRITISH COLUMBIA BY WEDNESDAY
 
   
..DIGGING/AMPLIFYING INTO THE NORTHERN PLAINS BY THURSDAY
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND WITH A SLIGHT WEIGHT TOWARD  
THE 12Z GFS AND 00Z ECMWF  
CONFIDENCE: ABOVE AVERAGE  
 
MODELS HAVE ALSO TRENDED INTO BETTER AGREEMENT WITH THIS  
SYSTEM...AND THE 12Z GFS HAS ALSO COME INTO FAIRLY GOOD ALIGNMENT  
WITH THE MORE CONSISTENT (OVER THE PAST SEVERAL MODEL CYCLES)  
ECMWF SOLUTION. THE 12Z NAM IS CLOSE AS WELL...ALTHOUGH IT IS THE  
STRONGEST WITH THE DEPICTION ALOFT OF THE EVENTUAL CYCLONE. THE  
00Z UKMET IS A LITTLE FASTER...PROBABLY DUE TO ITS FASTER EJECTION  
OF THE INITIAL TROUGH OVER THE GREAT LAKES AND NORTHEASTERN U.S.  
BUT OVERALL IS NOT MUCH DIFFERENT FROM OTHER MODELS WITH THIS  
SYSTEM. GIVEN THE GOOD AGREEMENT WITH THIS SYSTEM...A GENERAL  
MODEL BLEND IS PREFERRED...
WITH A SLIGHT WEIGHT TOWARD THE 12Z GFS  
AND 00Z ECMWF.  
 
WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML  
WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML  
 
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