484  
FXUS10 KWNH 230409  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1208 AM EDT MON OCT 23 2017  
 
VALID OCT 23/0000 UTC THRU OCT 26/1200 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
00Z MODEL EVALUATION...WITH LATEST MODEL PREFERENCES/CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
   
..SOUTHERN STREAM LOWER MS VALLEY CLOSED LOW
 
   
..SURFACE COLD FRONT SWEEPING ACROSS THE MS/TN VALLEYS
 
   
..NORTHERN STREAM TROUGH AMPLIFICATION OVER CENTRAL/EASTERN U.S
 
   
..DEEP PHASED CYCLONE OVER THE GREAT LAKES REGION BY TUES
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-NAM CONSENSUS...WEIGHTED TOWARD THE 12Z ECMWF  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
A SOUTHERN STREAM CLOSED LOW THAT HAS DEVELOPED OVER THE LOWER MS  
VALLEY IS EXPECTED TO ADVANCE EAST-NORTHEASTWARD OVER THE NEXT 12  
HOURS WHILE ELONGATING AND ACQUIRING A NEGATIVE TILT AS IT CROSSES  
THE TN VALLEY. THIS ENERGY ALONG WITH A DEVELOPING SURFACE LOW  
CENTER WILL LIFT NORTH UP ACROSS THE OH VALLEY AND INTO THE GREAT  
LAKES REGION ON MONDAY AS IT GETS CAUGHT UP AND GRADUALLY ABSORBED  
BY A STRONG NORTHERN STREAM TROUGH THAT WILL AMPLIFY SOUTHEAST  
ACROSS THE MIDWEST. THIS NORTHERN STREAM ENERGY IS ALREADY QUICKLY  
EJECTING ACROSS THE NORTHWEST U.S. AND THE LATEST MODELS ARE IN  
GOOD AGREEMENT IN THE DETAILS OF THIS SHARP AMPLIFICATION. THIS  
WILL LEAD TO A STRONG PHASED CYCLONE OVER THE GREAT LAKES BY  
TUESDAY AND A DEEP LONGWAVE TROUGH MOVING INTO THE EASTERN U.S.  
TUESDAY AND WEDNESDAY. A COLD FRONT WILL CROSS THE TN/OH VALLEYS  
MONDAY AND SWEEP TOWARD THE EASTERN SEABOARD ON TUESDAY BEFORE  
THEN MOVING OFFSHORE. THE MODELS HAVE COME INTO MUCH BETTER  
AGREEMENT WITH THE DETAILS OF THE PHASING OF NORTHERN AND SOUTHERN  
STREAM ENERGY AND THE DEEPENING SURFACE LOW CENTER...HOWEVER THE  
00Z NAM APPEARS TO BE STILL A TAD TOO WEAK WITH THE LOW CENTER  
OVER THE GREAT LAKES MONDAY AND TUESDAY. THE REMAINING MODELS ARE  
RATHER WELL CLUSTERED WITH THE EVOLUTION OF THIS SYSTEM AND ITS  
EXIT INTO ONTARIO THROUGH WEDNESDAY ALTHOUGH THERE IS SOME MODEST  
SPREAD WITH THE STRENGTH OF THE LOW CENTER AS IT EXITS NORTHEAST  
FROM THE GREAT LAKES. THE ECMWF HAS BEEN AMONG THE MOST CONSISTENT  
OF MODELS WITH THIS SYSTEM OVER THE LAST COUPLE OF DAYS...AND SO  
THE PREFERENCE WILL BE A NON-NAM CONSENSUS WEIGHTED TOWARD THE  
ECMWF.  
 
   
..SHORTWAVE DIGGING TOWARD THE NORTHERN PLAINS TUES NIGHT/WED
 
   
..ASSOCIATED SURFACE LOW OVER SOUTHERN CANADA
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF THE 00Z GFS/12Z ECMWF  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
A NORTHERN STREAM SHORTWAVE WILL BE QUICK TO DROP SOUTHEAST ACROSS  
SOUTHERN CANADA AND TOWARD THE NORTHERN PLAINS AND UPPER MS VALLEY  
TUESDAY NIGHT AND WEDNESDAY ALONG WITH A SURFACE WAVE. THE 00Z NAM  
AND 12Z CMC ARE A LITTLE SLOWER THAN THE 00Z GFS/12Z UKMET AND 12Z  
ECMWF. THE GFS AND ECMWF ARE BETTER CLUSTERED AND HAVE EXCELLENT  
ENSEMBLE SUPPORT...AND SO A GFS/ECMWF BLEND WILL BE PREFERRED.  
 
   
..SHORTWAVE TROUGH APPROACHING THE PACIFIC NORTHWEST BY WED
 
   
..AMPLIFYING OUT ACROSS CENTRAL/NORTHERN PLAINS BY THURS
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF THE 00Z GFS/12Z ECMWF  
CONFIDENCE: AVERAGE  
 
A NORTHERN STREAM SHORTWAVE OVER THE GULF OF AK ON TUESDAY IS  
FORECAST BY THE MODELS TO DROP IN ACROSS THE PACIFIC NORTHWEST BY  
WEDNESDAY WHICH VERY QUICKLY EJECTS OUT ACROSS THE CENTRAL AND  
NORTHERN PLAINS BY THURSDAY WHILE ALSO AMPLIFYING. THIS WILL LEAD  
TO A STRENGTHENING LOW CENTER WHICH INITIALLY COMES IN ACROSS  
BRITISH COLUMBIA BY TUESDAY NIGHT AND THEN REDEVELOPS OVER  
SOUTHERN ALBERTA BEFORE THEN DROPPING SOUTHEAST ACROSS THE  
NORTHERN PLAINS AND UPPER MIDWEST BY LATER WEDNESDAY AND THURSDAY.  
THE MODELS ARE IN GOOD AGREEMENT AS THE SYSTEM ARRIVES IN ACROSS  
BRITISH COLUMBIA...BUT 00Z NAM BECOMES A NORTHERLY OUTLIER WITH  
THE TRACK OF THE LOW CENTER ACROSS SOUTHERN CANADA THEREAFTER. THE  
GLOBAL MODELS ARE ALL CLUSTERED FARTHER SOUTH OVER THE NORTHERN  
PLAINS AND EVENTUALLY THE UPPER MIDWEST BUT HAVE SOME TIMING  
DIFFERENCES...WITH THE 00Z GFS THE FASTEST...AND THE 12Z CMC/ECMWF  
SOLUTIONS THE SLOWEST. THE 12Z UKMET TENDS TO BE FASTER LIKE THE  
GFS BUT IS FARTHEST SOUTH WITH ITS LOW TRACK. THERE ARE A FAIR  
NUMBER OF 12Z EURO ENSEMBLE MEMBERS THAT ARE FASTER THAN THE  
OPERATIONAL ECMWF AND SUPPORT A TIMING THAT IS ESSENCE MIDWAY  
BETWEEN THE GFS AND ECMWF. THERE ARE SOME 18Z GEFS AND 12Z  
CANADIAN MEMBERS THAT LIKE THIS IDEA AS WELL...AND SO A BLEND OF  
THE GFS AND ECMWF WILL BE PREFERRED AT THIS TIME.  
 
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ORRISON  
 

 
 
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