058  
FXUS10 KWNH 170644  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
143 AM EST FRI NOV 17 2017  
 
VALID NOV 17/0000 UTC THRU NOV 20/1200 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
00Z INITIAL MODEL PREFERENCES ALONG WITH CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
MODEL INITIALIZATION ERRORS APPEAR NEGLIGIBLE WITH RESPECT TO  
THEIR FORECASTS  
 
LEAD SHORTWAVE TRACKING ACROSS SOUTHERN CANADA THROUGH FRIDAY NIGHT  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
A LEAD NORTHERN STREAM SHORTWAVE TRACKING EASTWARD FROM ALBERTA TO  
HUDSON BAY WILL SUPPORT A SURFACE LOW WITH A TRAILING COLD FRONT.  
THIS BOUNDARY WILL CROSS THE NORTHERN PLAINS EARLY FRIDAY, AND  
THEN REACH THE NORTHERN GREAT LAKES BY FRIDAY NIGHT WHILE THE  
PARENT LOW LIFTS WELL TO THE NORTH OVER NORTHERN MANITOBA. THE  
NAM BECOMES SLIGHTLY FASTER WITH THE FRONTAL PROGRESSION BY FRIDAY  
NIGHT OVER WISCONSIN AND MICHIGAN, BUT DOES NOT DIFFER ENOUGH TO  
DISCOUNT IT FROM THE PREFERENCES.  
 
LARGE STORM SYSTEM OVER THE EASTERN U.S. THIS WEEKEND  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 00Z GFS/12Z ECMWF/12Z EC MEAN  
CONFIDENCE: AVERAGE  
 
BEHIND THE LEAD SHORTWAVE IS A MUCH LARGER UPPER LEVEL TROUGH THAT  
IS CURRENTLY SITUATED OVER THE PACIFIC NORTHWEST. THIS INITIALLY  
POSITIVELY TILTED TROUGH IS EXPECTED TO TRAVERSE THE CONTINENTAL  
U.S. AND BECOME A FULL LATITUDE TROUGH AS IT CROSSES THE PLAINS  
AND MIDWEST. A SURGE OF SHORTWAVE ENERGY BEHIND THE TROUGH IN  
NORTHWEST FLOW WILL LIKELY RESULT IN THIS FEATURE ACQUIRING  
NEGATIVE TILT AS IT APPROACHES THE NORTHEAST U.S. THIS WILL  
SUPPORT THE DEVELOPMENT OF A STRONG SURFACE LOW TRACKING FROM THE  
OHIO VALLEY TO SOUTHERN QUEBEC. THE NAM BECOMES A NOTABLE  
SOUTHERN OUTLIER WITH THE SURFACE LOW BY SATURDAY, AND ALSO  
CONSIDERABLY WEAKER. THE 18Z GEFS MEAN IS ON THE NORTHERN EDGE OF  
THE GUIDANCE, AND THE EC MEAN IS NEAR THE MODEL CONSENSUS. WITH  
THE GFS AND ECMWF CLOSE TO THE EC MEAN WITH THE SURFACE LOW, A  
BLEND OF THESE THREE MODELS SHOULD SUFFICE WELL FOR NOW.  
 
TROUGH APPROACHING THE PACIFIC NORTHWEST LATER ON SUNDAY  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
A LARGE UPPER LEVEL TROUGH OVER THE GULF OF ALASKA WILL SLOWLY  
SETTLE SOUTHWARD OFF THE BRITISH COLUMBIA COAST AS A POSITIVELY  
TILTED FEATURE, WITH A SURFACE LOW TRACKING INLAND JUST NORTH OF  
VANCOUVER ISLAND. THE TRAILING COLD FRONT IS EXPECTED TO REACH  
WESTERN WASHINGTON BY SUNDAY EVENING. THE OVERALL MASS FIELD  
DIFFERENCES ARE RELATIVELY MINOR FOR THIS SYSTEM AND A GENERAL  
MODEL BLEND SHOULD WORK WELL.  
 
WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML  
WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML  
 
HAMRICK  
 

 
 
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