292  
FXUS10 KWNH 180657  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
156 AM EST SAT NOV 18 2017  
 
VALID NOV 18/0000 UTC THRU NOV 21/1200 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
00Z MODEL ASSESSMENT INCLUDING PREFERENCES AND CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
MODEL INITIALIZATION ERRORS APPEAR NEGLIGIBLE WITH RESPECT TO  
THEIR FORECASTS  
 
LARGE STORM SYSTEM OVER THE EASTERN U.S. THIS WEEKEND  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 00Z GFS/00Z ECMWF BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
A LARGE FULL LATITUDE UPPER LEVEL TROUGH CURRENTLY OVER THE  
CENTRAL U.S. WILL CONTINUE TO REMAIN AMPLIFIED AS IT REACHES THE  
EAST COAST BY SUNDAY. 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. A SECONDARY TROUGH THEN  
CROSSES THE MID-ATLANTIC REGION SUNDAY NIGHT BEFORE HEIGHTS RISE  
AGAIN. IN TERMS OF THE MODELS, THE GFS AND THE GEFS MEAN ARE BOTH  
FASTER WITH THE COLD FRONT REACHING THE EAST COAST, AND THE NAM  
AND ECMWF ON THE SLOWER SIDE OF THE GUIDANCE. THE CMC ALSO  
BECOMES PROGRESSIVE ONCE THE SYSTEM EXITS THE COAST. THE NAM IS  
NOW MUCH CLOSER TO THE MODEL CONSENSUS COMPARED TO ITS RUN LAST  
NIGHT, ALTHOUGH IT IS STRONGER WITH THE SECONDARY TROUGH ACROSS  
THE MID-ATLANTIC REGION SUNDAY NIGHT AND INTO MONDAY. THE 00Z  
ECMWF TRENDED A LITTLE FASTER AND IS CLOSE TO THE MODEL CONSENSUS.  
A BLEND OF THE GFS AND ECMWF WOULD YIELD A SUITABLE TIMING OF THE  
FRONTAL PASSAGE.  
 
NORTHERN PORTION OF TROF TRACKING EASTWARD ACROSS SOUTHERN CANADA  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 00Z ECMWF/00Z GFS BLEND  
CONFIDENCE: AVERAGE  
 
PART OF THE ENERGY EMERGING FROM THE GULF OF ALASKA IS EXPECTED TO  
BREAK OFF AND TRACK EASTWARD ACROSS SOUTHERN CANADA SUNDAY AND  
INTO MONDAY WITHIN THE NORTHERN STREAM FLOW. A RELATIVELY DEEP  
SURFACE WAVE JUST NORTH OF US BORDER WITH A FRONT ENTERING THE  
NORTHERN PLAINS LATE MONDAY IS PREDICTED BY THE MODEL GUIDANCE. A  
BLEND OF THE FASTER GFS AND SLOWER ECMWF SHOULD YIELD THE BEST  
POSITION OF THE SURFACE LOW.  
 
BASE OF TROUGH APPROACHING THE PACIFIC NORTHWEST SUNDAY  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 00Z ECMWF/12Z EC MEAN  
CONFIDENCE: SLIGHTLY BELOW 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. AN ATMOSPHERIC RIVER OF  
DEEP PACIFIC MOISTURE IS EXPECTED TO ACCOMPANY THIS FEATURE. THE  
OVERALL MASS FIELD DIFFERENCES ARE RELATIVELY MINOR FOR THIS  
SYSTEM THROUGH 48 HOURS AND A GENERAL MODEL BLEND SHOULD WORK WELL  
THROUGH SUNDAY AFTERNOON. BEYOND THAT TIME, MODEL DIFFERENCES  
BECOME MUCH MORE NOTICEABLE, WITH THE CMC INDICATING A DEEPER AND  
MORE PROGRESSIVE TROUGH, AND THE NAM/GFS INDICATING MORE ZONAL  
FLOW. WITH THE EXPECTATION THAT THE TROUGH WILL PERSIST BEYOND  
SUNDAY EVENING, IN CONTRAST TO THE GFS/NAM, THE ECMWF ALONG WITH  
THE EC MEAN, ARE PREFERABLE SOLUTIONS FOR NOW.  
 
WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML  
WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML  
 
HAMRICK  
 

 
 
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