820  
FXUS10 KWNH 261651  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1151 AM 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...  
 
12Z NAM/GFS EVALUATION AND PRELIMINARY PREFERENCES/CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
   
..NORTHERN STREAM SHORTWAVE CROSSING THE NORTHEAST WED/THURS
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: SLIGHTLY 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. THE 00Z ECMWF WAS THE  
STRONGEST SOLUTION BY 28/12Z WITH THIS ENERGY AS IT CROSSES THE  
NORTHEAST WITH THE 12Z NAM SIMILAR WHILE THE 12Z GFS AND 00Z  
UKMET/CMC ARE SIMILAR WITH THE 12Z GFS SLIGHTLY MORE PROGRESSIVE.  
THIS IS MAINLY DRY WITH A STRONG OFFSHORE FLOW...THE GREATEST  
DIFFERENCE IS IN THE WIND FORECAST WHICH IS HIGHER IN THE 12Z GFS.  
 
 
...PACIFIC WAVE ENTERING PAC NW TONIGHT AND MOVING SOUTHEAST  
THROUGH THE NORTHERN ROCKIES/PLAINS THROUGH THURS...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: AVERAGE  
 
A LOW WILL PERSISTS NEAR THE SOUTHERN PORTION OF THE GULF OF AK  
THROUGH THE REST OF THE WORK WEEK. SHORTWAVE ENERGY ROUNDING THIS  
LOW IS WEAKENING THE RIDGE OVER THE PACIFIC CONUS COAST TODAY AND  
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 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 GFS AND 00Z CMC SUGGESTING MORE  
PHASING AND SOME SHORTWAVE AMPLIFICATION TOWARD THE UPPER MIDWEST.  
THE 00Z ECMWF AND 00Z UKMET ARE THE WEAKEST/FLATTEST WITH THE 00Z  
CMC. WILL PREFER A GENERAL MODEL BLEND FOR NOW WITH AN EVEN MIX OF  
MORE AND LESS AMPLIFIED TROUGH ACTION. THE FLATTER 00Z ECMWF  
RESULTS IN MORE PRECIP OVER THE NORTHERN ROCKIES WHILE THE 12Z GFS  
IS DRIER. LOW PRESSURE THEN DEVELOPS OVER THE UPPER MIDWEST  
THURSDAY WITH GENERAL AGREEMENT AS IT PROGRESSES THROUGH THE  
GREAT LAKES INTO FRIDAY.  
 
JACKSON  
 
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