003  
FXUS10 KWNH 240658  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
258 AM EDT TUE OCT 24 2017  
 
VALID OCT 24/0000 UTC THRU OCT 27/1200 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
00Z MODEL EVALUATION...WITH LATEST MODEL PREFERENCES/CONFIDENCE  
 
***NOTE: THE 00Z ECMWF WAS NOT AVAILABLE FOR ANALYSIS/ASSESSMENT***  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
   
..DEEP PHASED CYCLONE OVER THE GREAT LAKES REGION BY TUES
 
   
..CLIPPER SHORTWAVE DIGGING ACROSS THE MIDWEST
 
   
..LONGWAVE TROUGH AMPLIFICATION OVER THE EASTERN U.S
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF THE 00Z GFS/12Z ECMWF  
CONFIDENCE: ABOVE AVERAGE  
 
THE MODELS ARE IN VERY GOOD AGREEMENT THROUGH TUESDAY IN DEPICTING  
A DEEPLY OCCLUDED AND PHASED CYCLONE OVER THE GREAT LAKES REGION  
AS A COLD FRONT GRADUALLY PUSHES ACROSS THE MID-ATLANTIC AND  
SOUTHEAST COASTAL PLAIN AND THEN OFFSHORE. HOWEVER...THE NORTHERN  
PORTION OF THE FRONT INVOLVING NEW ENGLAND WILL BE VERY SLOW TO  
ADVANCE EAST AS IT BECOMES ALIGNED NEARLY PARALLEL TO THE BACKING  
DEEP LAYER SOUTHERLY FLOW AROUND THE EAST SIDE OF THE UPPER  
TROUGH. A REINFORCING CLIPPER-TYPE SHORTWAVE AND WEAK SURFACE LOW  
WILL BE DIGGING ACROSS THE MIDWEST THROUGH EARLY WEDNESDAY AND  
THIS WILL DIG INTO THE BASE OF THE EASTERN U.S. LONGWAVE TROUGH  
AND ALLOW IT TO TAKE ON A NEGATIVE TILT BY WEDNESDAY NIGHT ACROSS  
THE CENTRAL/SOUTHERN APPALACHIANS AND MID-ATLANTIC REGION. ON  
THURSDAY THE TROUGH SHOULD PIVOT NORTHEAST ACROSS NEW ENGLAND AND  
WILL ALSO BE RESPONSIBLE FOR ALSO DEVELOPING A SURFACE LOW  
PRESSURE WAVE ALONG THE AFOREMENTIONED FRONT OVER SOUTHERN  
ENGLAND. THIS WILL BE A DRIVER OF SOME HEAVY TO POSSIBLE EXCESSIVE  
RAINFALL FOR SOUTHERN AND EASTERN NEW ENGLAND. THE 00Z NAM BECOMES  
A STRONGER OUTLIER WITH THE CLIPPER SHORTWAVE THAT DIGS SOUTHEAST  
THROUGH THE MIDWEST AND ULTIMATELY LEADS TO A SLOWER AND GENERALLY  
STRONGER TROUGH EVOLUTION OVER THE MID-ATLANTIC AND NORTHEAST  
THROUGH WEDNESDAY AND THURSDAY. THE 00Z UKMET ON THE OTHER HAND IS  
A FAST OUTLIER WITH THE TROUGH EVOLUTION. THE BETTER MODEL  
CLUSTERING RESIDES WITH THE 00Z GFS AND 12Z ECMWF...AND HAS  
EXCELLENT ENSEMBLE SUPPORT...SO A BLEND OF THESE SOLUTIONS 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...THROUGH 60 HOURS  
00Z GFS...AFTER 60 HOURS  
CONFIDENCE: SLIGHTLY ABOVE 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 SHARPLY 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 AND TO SOME EXTENT THE 00Z CMC  
BECOME NORTHERLY OUTLIERS WITH THE TRACK OF THE LOW CENTER ACROSS  
SOUTHERN CANADA THEREAFTER. THE 00Z CMC THOUGH DOES COME INTO  
BETTER AGREEMENT WITH THE 00Z GFS/00Z UKMET AND 12Z ECMWF BY  
THURSDAY WHICH ARE ALL CLUSTERED A BIT FARTHER SOUTH WITH THE LOW  
TRACK. OVERALL...THE NAM BECOMES A STRONGER OUTLIER WITH ITS  
TROUGH AMPLIFICATION BY LATER THURSDAY AND EARLY FRIDAY AS THE  
SYSTEM DROPS ACROSS THE MIDWEST. THE UKMET WHICH HAD BEEN A BIT  
TOO PROGRESSIVE HAS TRENDED A LITTLE SLOWER AND IS CLOSER TO THE  
GFS AND ECMWF WHICH ARE RATHER WELL CLUSTERED...ALTHOUGH IT DOES  
APPEAR THAT THE ECMWF MAY BE A BIT TOO SLOW BY THE END OF THE  
PERIOD AS THE 12Z ECENS MEAN AND 00Z GEFS MEAN SHOW VERY STRONG  
SUPPORT FOR THE OPERATIONAL GFS. WILL PREFER A BLEND OF THE GFS  
AND ECMWF THROUGH 60 HOURS...AND THEN FAVOR THE GFS THEREAFTER.  
 
WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML  
WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML  
 
ORRISON  
 

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab HPC Page Main Text Page