344  
FXUS10 KWNH 230639  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
238 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 00Z 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/UKMET/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 00Z CMC ARE A LITTLE SLOWER THAN THE 00Z GFS/UKMET AND ECMWF.  
THE GFS/UKMET AND ECMWF ARE BETTER CLUSTERED AND HAVE EXCELLENT  
ENSEMBLE SUPPORT...AND SO A GFS/UKMET/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/ECMWF  
CONFIDENCE: SLIGHTLY BELOW 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 AND  
LIKELY IS TOO STRONG AS WELL. 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 00Z CMC/ECMWF SOLUTIONS THE SLOWEST. THE 00Z  
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. THE BULK  
OF THE 00Z GEFS MEMBERS ARE ALSO A BIT SLOWER AND WEST OF THE  
OPERATIONAL GFS BY THE END OF THE PERIOD. THUS...BASED ON THE  
LATEST TRENDS AND AVAILABLE ENSEMBLE GUIDANCE...A BLEND OF THE GFS  
AND ECMWF WILL STILL BE PREFERRED. CONFIDENCE THOUGH IS A BIT LOW  
CONSIDERING THE SPREAD IN THE DETERMINISTIC GUIDANCE.  
 
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ORRISON  
 

 
 
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