627  
FXUS10 KWNH 241842  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
241 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 OF THE 12Z ECMWF...UKMET...AND 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 MODEL RUNS HAVE  
CONTINUED TO CONVERGE. THE EUROPEAN MODEL HAS GENERALLY 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 12Z ECMWF WAS SLIGHTLY SLOWER WITH THE TROUGH  
EJECTION THAN ITS 00Z RUN...AND SLIGHTLY MORE AMPLIFIED WITH THE  
TROUGH AS WELL. DESPITE THIS...THE 12Z NAM CONTINUES TO REPRESENT  
THE SLOWEST SOLUTION...WITH THE CLIPPER SHORTWAVE DIGGING MORE  
SUBSTANTIALLY EARLIER IN THE RUN. IT IS ENOUGH OF A DISPARITY TO  
EXCLUDE THE NAM FROM THE MODEL PREFERENCE FOR THESE SYSTEMS. THE  
12Z UKMET REMAINS ON THE FASTER END OF MODEL SPREAD...BUT HAS  
TRENDED TO BE MUCH CLOSER TO THE GFS AND ECMWF. FINALLY...THE 12Z  
CMC CONTINUES TO SHOW HIGHER SURFACE PRESSURES ON WEDNESDAY AND  
THURSDAY OVER THE EASTERN CONUS...AND HIGHER HEIGHTS ALOFT ON  
THURSDAY NIGHT AND FRIDAY. THE DIFFERENCE IS SLIGHTLY SMALLER THAN  
IN THE 00Z MODEL CYCLE...BUT STILL ENOUGH OF A DIFFERENCE (AND A  
RECENT BIAS) THAT IT HAS ALSO BEEN EXCLUDED FROM THE PREFERENCE  
FOR THESE SYSTEMS.  
 
UPDATES FROM PRELIMINARY PREFERENCE: ADD THE 12Z UKMET TO THE  
ECMWF/GFS BLEND. THE GFS AND ECMWF CONTINUE TO REPRESENT THE MORE  
CONSISTENT SOLUTIONS DESPITE A CONTINUED REDUCTION IN MODEL SPREAD  
AS COMPARED TO PREVIOUS MODEL CYCLES. THE UKMET HAS TRENDED  
SUBSTANTIALLY ENOUGH IN THAT DIRECTION TO BE INCLUDED IN THE BLEND.  
 
   
..SHORTWAVE TROUGH REACHING BRITISH COLUMBIA BY WEDNESDAY
 
   
..DIGGING/AMPLIFYING INTO THE NORTHERN PLAINS BY THURSDAY
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-CMC BLEND WITH A SLIGHT WEIGHT TO 12Z 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  
12Z UKMET CONTINUES TO BE A LITTLE FASTER (ALBEIT NOT AS MUCH AS  
ITS 00Z RUN)...PROBABLY DUE TO ITS FASTER EJECTION OF THE INITIAL  
TROUGH OVER THE GREAT LAKES AND NORTHEASTERN US. OVERALL THE UKMET  
IS NOT MUCH DIFFERENT FROM OTHER MODELS WITH THIS SYSTEM. THE 12Z  
CMC SHOWS HIGHER HEIGHTS THROUGH MUCH OF THE TROUGH...AND AT  
T+72HR IS ABOUT 60M HIGHER AT 500MB THAN THE GEFS ENSEMBLE MEAN IN  
THE CORE OF THE TROUGH. THIS IS ENOUGH OF A DIFFERENCE THAT IT WAS  
EXCLUDED FROM THE PREFERENCE FOR THIS SYSTEM. OTHERWISE...A  
GENERAL BLEND IS PREFERRED...WITH A SLIGHT WEIGHT GIVEN TO THE  
CONSISTENT ECMWF SOLUTION.  
 
UPDATES FROM PRELIMINARY PREFERENCE: REMOVE THE 12Z CMC. AS OTHER  
MODELS HAVE CONTINUED TO COME INTO BETTER AGREEMENT...THE CMC  
SHOWS HIGHER HEIGHTS ALOFT THROUGH MUCH OF THE CENTRAL U.S. THE  
DISPARITY IS ENOUGH TO REMOVE IT FROM THE PREFERENCE FOR THIS  
SYSTEM.  
 
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