461  
FXUS10 KWNH 251633  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1132 AM 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-ECMWF 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 00Z ECMWF WAS THE  
STRONGEST SOLUTION WITH THIS ENERGY AS IT CROSSES THE  
NORTHEAST...WITH THE REMAINING MODELS RATHER WELL CLUSTERED AROUND  
A WEAKER SOLUTION. WILL PREFER A NON-ECMWF BLEND AS A RESULT FOR  
THE TIME BEING.  
 
   
..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.  
 
   
..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 GFS AND 00Z UKMET  
CONFIDENCE: 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 00Z UKMET AND 00Z CMC ARE WEAKER...WITH THE  
00Z ECMWF THE WEAKEST/FLATTEST. 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 UKMET AND CMC HINT AT THESE FEATURES BUT ARE LESS  
DEFINED...AND THE ECMWF ESSENTIALLY HAS NO WAVE DEVELOPMENT AT ALL  
OVER THIS REGION. THE NAM GENERALLY APPEARS TO BE TOO STRONG ALOFT  
LATE IN THE PERIOD WHEN COMPARED TO THE 06Z GEFS MEAN AND 00Z  
ECENS MEAN. THE ECMWF THOUGH IS EVEN A BIT WEAKER THAN THE LATEST  
ENSEMBLE MEANS...AND IS LIKELY TOO WEAK. WITH AN ATTEMPT TO  
COMPROMISE...WILL PREFER A BLEND OF THE GFS AND UKMET WHICH AT  
LEAST WOULD SUPPORT THE IDEA OF A COLD FRONT/INVERTED TROUGH AND  
POSSIBLY A WEAK SURFACE WAVE IMPACTING THE CENTRAL/NORTHERN PLAINS  
AND UPPER MIDWEST THROUGH THURS.  
 
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