248  
FXUS10 KWNH 251901  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
200 PM EST MON DEC 25 2017  
 
VALID DEC 25/1200 UTC THRU DEC 29/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z MODEL EVALUATION INCLUDING PREFERENCES AND FORECAST CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
   
..NEGATIVELY TILTED TROUGH SWINGING THROUGH THE NORTHEAST
 
   
..DEEPENING LOW CROSSING THE GULF OF MAINE
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
A RAPIDLY AMPLIFYING AND NEGATIVELY TILTING SHORTWAVE LIFTING  
ACROSS THE NORTHEAST THIS MORNING WILL CONTINUE TO FOSTER A  
DEEPENING AREA OF LOW PRESSURE THAT WILL CROSS THE GULF OF MAINE  
AND THEN ACROSS THE CANADIAN MARITIMES TONIGHT. THE MODELS ARE IN  
GOOD AGREEMENT WITH THE MASS FIELD EVOLUTION OF THE SYSTEM OVER  
THE NEXT 12 TO 24 HOURS AS THE LOW CENTER PULLS AWAY...SO A  
GENERAL MODEL BLEND WILL BE PREFERRED.  
 
   
..NORTHERN STREAM SHORTWAVE CROSSING THE NORTHEAST WED/THURS
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-GFS BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
AFTER THE EXIT OF THE STRONG NORTHEAST U.S. LOW  
CENTER/SHORTWAVE...THE DEEP NEGATIVE HEIGHT ANOMALY/VORTEX OVER  
NORTHERN ONTARIO WILL BEGIN TO WEAKEN AS A MEAN LAYER RIDGE/HIGH  
DEVELOPS FROM NEAR THE DAVIS STRAIT AND THEN ADVANCES SOUTHWEST  
TOWARD HUDSON BAY. THE REMNANT NEGATIVE HEIGHT ANOMALY WILL  
ESSENTIALLY BECOME SUPPRESSED AND SQUASHED SOUTHEASTWARD ACROSS  
SOUTHEAST CANADA AND THE NORTHEAST BY WED/THURS AS A  
POSITIVELY-TILTED SHORTWAVE TROUGH. THE 12Z ECMWF TRENDED A LITTLE  
WEAKER AND IS NOW CLOSE TO THE MODEL CONSENSUS WITH THIS  
TROUGH...HOWEVER...THE 12Z GFS NOW APPEARS TO BE A TAD TOO  
PROGRESSIVE TO ADVANCE THE TROUGH ACROSS THE NORTHEAST AND  
ADJACENT AREAS OF SOUTHEAST CANADA. THE GFS IS ACTUALLY EVEN A BIT  
FASTER THAN THE 12Z GEFS MEAN WHICH SUGGESTS ITS SOMEWHAT OF AN  
OUTLIER. WILL SUPPORT THE SOMEWHAT SLOWER AND WELL-CLUSTERED  
CONSENSUS AWAY FROM THE GFS BASED ON THE LATEST TRENDS.  
 
   
..WEAK ELONGATED SHORTWAVE IMPACTING THE NORTHWEST TODAY
 
   
..ENERGY SHEARING DOWNSTREAM ACROSS THE GREAT BASIN/ROCKIES
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
THE LATEST GOES-16 RGB AIRMASS IMAGERY SHOWS A WELL-DEFINED AND  
ELONGATED AXIS OF SHORTWAVE ENERGY EXTENDING FROM JUST OFFSHORE  
THE PACIFIC NORTHWEST AND VANCOUVER ISLAND SOUTHEAST DOWN ACROSS  
THE NORTHERN GREAT BASIN AND NORTHERN ROCKIES. THIS ENERGY WILL BE  
EMBEDDED WITHIN STRONG NORTHWEST MID LEVEL FLOW AND WILL BE  
SHEARING DOWNSTREAM TOWARD THE CENTRAL HIGH PLAINS THROUGH TUESDAY  
BEFORE DAMPENING OUT. THE GUIDANCE IS IN REASONABLY GOOD AGREEMENT  
WITH THIS...AND SO A GENERAL MODEL BLEND WILL BE PREFERRED.  
 
   
..WEAK SHEARING ENERGY ACROSS THE GULF COAST STATES BY WED
 
   
..WEAK SURFACE WAVE DEVELOPMENT OFF THE SOUTHEAST LATE WED
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF THE 12Z UKMET AND 12Z ECMWF  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
SOME OF THE REMNANT ENERGY SHEARING OUT OF THE INTERMOUNTAIN WEST  
AND ACROSS THE PLAINS THROUGH TUES WILL CROSS THE GULF COAST  
STATES AND INTERACT WITH A DEVELOPING FRONTAL ZONE ACROSS THE  
NORTHERN GULF OF MEXICO BY EARLY WED. THERE ARE SOME HINTS THAT  
THIS ENERGY WILL ENCOURAGE A WEAK WAVE OF LOW PRESSURE TO DEVELOP  
OFFSHORE THE SOUTHEAST COASTAL PLAIN LATE WED...BUT THE GUIDANCE  
OVERALL IS QUITE FLAT/SHEARED WITH THE ENERGY AND SO A SIGNIFICANT  
WAVE IS NOT LIKELY TO FORM. HAVING SAID THAT...THE 12Z NAM AND 12Z  
CMC ARE THE STRONGEST SOLUTIONS AND DO SUPPORT A SOMEWHAT  
BETTER-DEFINED LOW OFFSHORE THE CAROLINAS BY MIDDAY WED. THE 12Z  
UKMET AND 12Z ECMWF ARE BOTH WEAKER/FLATTER. THE 12Z GFS IS WEAK  
WITH ANY WAVE DEVELOPMENT...HOWEVER...IT TENDS TO BACK THE 700/500  
MB FLOW A BIT MORE OVER THE LOWER MS VALLEY/GULF COAST STATES  
WHICH ALLOWS IT TO FOSTER OVERRUNNING W/SW FLOW OVER THE FRONTAL  
ZONE OVER THE NORTHERN GULF OF MEXICO AND THUS A WETTER SOLUTION  
OVER THE GULF COAST STATES. THE GFS IS AN OUTLIER IN THIS REGARD.  
THE WEAKER/FLATTER CONSENSUS TOWARD THE UKMET/ECMWF SOLUTIONS WILL  
BE PREFERRED GIVEN THE STRENGTH OF SUPPRESSING NORTHERN STREAM  
FLOW STRETCHING FROM THE MIDWEST TO THE MID-ATLANTIC REGION ALONG  
WITH STRONG ARCTIC HIGH PRESSURE OVER THESE AREAS WHICH WILL ALSO  
HELP SUPPRESS ANY STRENGTHENING BAROCLINIC ZONE. THIS WOULD LIKELY  
FOSTER A RELATIVELY DRIER SOLUTION.  
 
   
..NEXT PACIFIC WAVE ENTERING PAC NW LATE TUES/EARLY WED
 
   
..SHORTWAVE ENERGY DROPPING SOUTH THROUGH BRITISH COLUMBIA
 
   
..ENERGY ROLLING THROUGH THE NORTHERN ROCKIES/PLAINS BY THURS
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF THE 12Z UKMET/12Z ECMWF AND 12Z GEFS MEAN  
CONFIDENCE: SLIGHTLY BELOW AVERAGE  
 
A PORTION OF A SHORTWAVE TROUGH NEAR THE SOUTHERN PORTION OF THE  
GULF OF AK WILL PINCH OFF AND EJECT EAST INTO THE PACIFIC  
NORTHWEST BY LATE TUES AS A SEPARATE AND STRONGER SHORTWAVE TROUGH  
DIGS SOUTH ACROSS BRITISH COLUMBIA. THE INITIAL ENERGY WILL  
BASICALLY SHEAR OUT WITHIN STRONGER MID LEVEL NORTHWEST FLOW AND  
IN FAVOR OF THE NORTHERN STREAM ENERGY DROPPING SOUTH TOWARD  
SOUTHWEST CANADA. ALTHOUGH THE NORTHERN TROUGH WILL LIKELY CAPTURE  
WHATEVER REMNANT THERE IS OF THE PACIFIC SHORTWAVE...AND THE  
PHASED RESULTANT SHORTWAVE WILL THEN CROSS THE NORTHERN ROCKIES  
AND EJECT OUT INTO THE NORTHERN PLAINS AND PARTS OF THE MIDWEST BY  
THURS. THERE ARE SOME NOTABLE DIFFERENCES BY THURS AS THE ENERGY  
EJECTS EAST OF THE ROCKIES...WITH THE 12Z NAM AND 12Z GFS  
SUGGESTING MORE PHASING AND SOME SHORTWAVE AMPLIFICATION TOWARD  
THE UPPER MIDWEST. THE 12Z UKMET/12Z CMC AND 12Z ECMWF ARE ALL  
WEAKER/FLATTER...WITH THE CMC NOW THE FLATTEST SOLUTION. THE  
DIFFERENCES ALOFT RESULT IN THE NAM/GFS SOLUTIONS HAVING A  
STRONGER INVERTED TROUGH AND DEVELOPING SURFACE WAVE OVER PARTS OF  
WI BY THE END OF THE PERIOD. THE 12Z GEFS MEAN SUGGESTS THE NAM  
AND GFS ARE TOO STRONG WITH THE SHORTWAVE TROUGH OVER THE  
MIDWEST...BUT THAT THE NON-NCEP GUIDANCE IS TOO WEAK. AN ATTEMPT  
TO COMPROMISE WOULD SUGGEST A SOLUTION TOWARD A BLEND OF THE  
UKMET/ECMWF AND GEFS MEAN...WHICH DOWNPLAYS THE STRONGER NAM/GFS  
AND WEAKER CMC. CONFIDENCE IS SOMEWHAT LIMITED.  
 
PREVIOUS MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML  
PREVIOUS 500 MB FORECASTS AT  
WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML  
 
ORRISON  
 

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab HPC Page Main Text Page