916  
FXUS10 KWNH 261856  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
155 PM EST TUE DEC 26 2017  
 
VALID DEC 26/1200 UTC THRU DEC 30/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
FINAL NAM/GFS EVALUATION AND PREFERENCES/CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
   
..NORTHERN STREAM SHORTWAVE CROSSING THE NORTHEAST WED/THURS
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
PREFERENCE: NON CMC BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
THE DEEP NEGATIVE HEIGHT ANOMALY/VORTEX OVER NORTHERN ONTARIO WILL  
WEAKEN THROUGH TONIGHT AS A MEAN LAYER RIDGE/HIGH DEVELOPING NEAR  
THE DAVIS STRAIT ADVANCES SOUTHWEST TOWARD HUDSON BAY. THE REMNANT  
NEGATIVE HEIGHT ANOMALY/UPPER TROUGH WILL SHIFT SOUTHEAST ACROSS  
SOUTHEAST CANADA AND THE NORTHEAST CONUS WED/THURS AS A  
POSITIVELY-TILTED SHORTWAVE TROUGH FROM AN EXCEPTIONALLY DEEP LOW  
THAT PERSISTS OVER THE LABRADOR SEA. THERE IS GENERAL AGREEMENT ON  
THE TROUGH AXIS LOCATION OVER NEW ENGLAND AMONG 12Z GUIDANCE. AT  
28/12Z THE ECMWF AND NAM ARE SIMILAR AND FARTHER SOUTH THAN THE  
GFS AND UKMET WHICH ARE A BIT MORE PROGRESSIVE AND NORTH. THE CMC  
STANDS OUT AS THE FARTHEST NORTH AND LEAST PROGRESSIVE...SO IT IS  
SUGGESTED TO LEAVE OUT OF THE BLEND.  
 
 
...PACIFIC WAVE ENTERING PAC NW TONIGHT AND MOVING SOUTHEAST  
THROUGH THE NORTHERN ROCKIES/PLAINS THROUGH THURS...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
PREFERENCE: ECMWF AND NAM BLEND  
CONFIDENCE: AVERAGE  
 
A LOW WILL PERSISTS NEAR THE SOUTHERN PORTION OF THE GULF OF AK  
THROUGH THE REST OF THE WORK WEEK...AND WILL EVENTUALLY EJECT  
EAST. SHORTWAVE ENERGY ROUNDING THIS LOW IS WEAKENING THE RIDGE  
OVER THE PACIFIC CONUS COAST TODAY AND WILL SET UP AN ACTIVE  
PERIOD OVER THE NORTHWEST CONUS THROUGH THE REST OF THE WEEK. THE  
FIRST WAVE WILL REACH THE PACIFIC NORTHWEST TONIGHT AS A SEPARATE  
AND STRONGER SHORTWAVE TROUGH PERSISTS OFF BRITISH COLUMBIA. THE  
INITIAL ENERGY WILL 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 AND CROSSES THE GREAT LAKES FRIDAY. BY LATE  
THURSDAY THE GFS STANDS OUT AS MOST AMPLIFIED WHILE THE CMC IS  
MOST PROGRESSIVE. MEANWHILE THE UKMET IS THE LEAST PROGRESSIVE  
LEAVING THE NAM AND ECMWF AS QUITE COMPARABLE.  
   
..FRIDAY APPROACH OF GULF OF ALASKA LOW TO THE PAC NW
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
PREFERENCE: UKMET  
CONFIDENCE: AVERAGE  
 
THE LOW OVER SOUTHERN GULF OF ALASKA THIS WEEK EJECTS EAST AND  
APPROACHES THE PAC NW COAST AS AN OPEN WAVE TOWARD HOUR 84.  
AVERAGE UNCERTAINTY WITH STRENGTH/PROGRESSION IN GLOBAL  
OPERATIONAL AND ENSEMBLE MEANS IS SEEN. THE 12Z NAM IS THE  
FLATTEST WITH SIMILAR AMPLITUDES AMONG THE REST WITH TIMING  
DIFFERENCES APPARENT. BY 30/00Z THE GFS HAS THE FARTHEST EAST  
TROUGH AXIS/IS THE MOST PROGRESSIVE WHILE THE ECMWF AND CMC ARE  
FARTHEST WEST. THE UKMET IS IN BETWEEN THE GFS/ECMWF AND IS A GOOD  
AVERAGE.  
 
JACKSON  
 
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