534  
FXUS10 KWNH 250642  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
241 AM EDT WED OCT 25 2017  
 
VALID OCT 25/0000 UTC THRU OCT 28/1200 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
00Z MODEL EVALUATION...WITH LATEST MODEL PREFERENCES/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: NON-UKMET CONSENSUS  
CONFIDENCE: ABOVE AVERAGE  
 
THE MODELS ARE IN VERY GOOD AGREEMENT THROUGH THE PERIOD WITH THE  
DETAILS OF THE DEEPLY OCCLUDED AND PHASED CYCLONE OVER THE GREAT  
LAKES REGION GRADUALLY LIFTING NORTH UP ACROSS ONTARIO AND  
WEAKENING THROUGH WEDNESDAY. MEANWHILE THERE WILL BE A FRONT  
SITUATED JUST OFF THE MID-ATLANTIC COAST THAT WILL EXTEND NORTH  
AND INLAND ACROSS NEW ENGLAND. 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. THIS WILL  
LEAD TO A SURFACE DEVELOPING SOUTH OF LONG ISLAND ALONG THE FRONT.  
ON THURSDAY THE TROUGH SHOULD PIVOT NORTHEAST ACROSS NEW ENGLAND  
AND DRIVE A RAPIDLY DEEPENING LOW CENTER INLAND ACROSS EASTERN NEW  
ENGLAND...BEFORE THEN LIFTING UP INTO SOUTHEAST CANADA BY FRIDAY.  
THIS WILL BE A DRIVER OF SOME EXCESSIVE RAINFALL FOR SOUTHERN AND  
EASTERN NEW ENGLAND. PLEASE CONSULT THE LATEST QPFPFD AND QPFERD  
FOR MORE DETAILS ON THIS. REGARDING THE MASS FIELDS...THE MODELS  
HAVE COME INTO RATHER GOOD AGREEMENT WITH THE SURFACE AND UPPER  
LEVEL FEATURES...ALTHOUGH THERE ARE SOME MINOR TIMING DIFFERENCES.  
THE ONE MODEL WITH SOME DEEPER CONCERNS IS THE 00Z UKMET WHICH  
STILL TENDS TO HAVE A STRONGER SURFACE LOW THAN THE OTHER MODELS  
AS THE LOW EXITS NORTH OUT OF NEW ENGLAND BY FRIDAY. BASED ON THE  
MODEL CLUSTERING AND ENSEMBLE SUPPORT SEEN OTHERWISE...
A NON-UKMET  
CONSENSUS WILL BE PREFERRED.  
 
   
..SHORTWAVE TROUGH REACHING BRITISH COLUMBIA TODAY
 
   
..DIGGING/AMPLIFYING INTO THE NORTHERN PLAINS BY THURSDAY
 
   
..LONGWAVE TROUGH OVER THE CENTRAL U.S. BY FRIDAY/SATURDAY
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF THE 00Z NAM/GFS/UKMET  
CONFIDENCE: AVERAGE  
 
THE LATEST GUIDANCE IS IN VERY GOOD AGREEMENT IN TAKING A  
SHORTWAVE TROUGH IN ACROSS BRITISH COLUMBIA THROUGH TODAY AND THEN  
DIGGING IT RATHER SHARPLY SOUTHEAST ACROSS THE NORTHERN PLAINS AND  
MIDWEST ON THURSDAY. THIS WILL DRIVE LOW PRESSURE SOUTHEASTWARD  
FROM THE SOUTHWEST CANADIAN PRAIRIES AND TOWARD THE UPPER MIDWEST.  
LOW PRESSURE WILL THEN SLOW DOWN AND PIVOT INTO THE GREAT LAKES  
REGION FRIDAY AND SATURDAY AS A TRAILING COLD FRONT SWEEPS THROUGH  
THE PLAINS/MS VALLEY AND HEADS FOR THE OH/TN VALLEYS. THE 00Z  
CMC/ECMWF TEND TO DIG THEIR HEIGHT FALLS A BIT FARTHER SOUTH THAN  
THE 00Z NAM/GFS/UKMET ON FRIDAY AND SATURDAY...ALTHOUGH THEY DID  
TREND A BIT FARTHER NORTH WITH THEIR LATEST RUN. THE TRENDS OF THE  
LATEST UKMET AND ECMWF HAVE ALSO AT LEAST PUT THEIR SURFACE LOW  
POSITIONS MORE CLOSELY IN LINE WITH THE NAM/GFS/UKMET CLUSTER AND  
WITH BETTER ENSEMBLE SUPPORT. WILL STILL PREFER A BLEND OF THE  
NAM/GFS AND UKMET AT THIS TIME.  
 
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WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML  
 
ORRISON  
 

 
 
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