332  
FXUS10 KWNH 111643  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1142 AM EST MON DEC 11 2017  
 
VALID DEC 11/1200 UTC THRU DEC 15/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z MODEL EVALUATION WITH PRELIMINARY PREFERENCES AND CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
   
..LEAD SHORTWAVE OVER THE WESTERN GREAT LAKES TODAY
 
 
...PRIMARY SHORTWAVE OVER NRN ONTARIO DIGGING INTO GREAT LAKES AND  
NORTHEAST TUE-WED WITH DEVELOPING CYCLONE...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
MODEL SOLUTIONS ARE GENERALLY QUITE SIMILAR IN THEIR DEPICTION OF  
THE MASS FIELDS WITH THIS EVOLVING SYSTEM OVER THE NORTHEASTERN  
QUADRANT OF THE CONUS OVER THE NEXT FEW DAYS. THE INTENSITY AND  
POSITION OF THE SURFACE LOW THROUGH 13/12Z IS EXTREMELY CLOSE FOR  
BOTH THE OPERATIONAL MODELS AND THE GEFS AND ECMWF ENSEMBLE MEANS.  
THEREFORE...A GENERAL MODEL BLEND IS PREFERRED WITH RELATIVELY  
HIGH CONFIDENCE. FOR DETAIL DIFFERENCES: ENSEMBLE SENSITIVITY  
ANALYSIS SHOWS THAT THE LARGEST PORTION OF VARIANCE WITH THE SEA  
LEVEL PRESSURE FIELDS IS EXPLAINED BY TIMING DIFFERENCES AS THE  
SURFACE LOW OCCLUDES AND TRACKS THROUGH INTERIOR NEW ENGLAND. AND  
THIS VARIANCE IS WELL CORRELATED WITH THE HEIGHT FIELDS ASSOCIATED  
WITH THE UPSTREAM WAVES: HIGHER HEIGHTS WITH THE WAVES TODAY TEND  
TO CORRELATE WITH SLIGHTLY SLOWER SOLUTIONS.  
 
...STRONG SHORTWAVE IN NERN PACIFIC NEAR 45N/135W TODAY ROUNDING  
THE WESTERN RIDGE THROUGH TUESDAY...   
..DIGGING INTO CENTRAL US TUESDAY NIGHT AND WEDNESDAY
 
 
...SECONDARY SHORTWAVE EMBEDDED IN NWLY FLOW DIGGING INTO NRN  
PLAINS AND GREAT LAKES LATE WED INTO THU...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF 12Z GFS / 00Z ECMWF / 00Z CMC  
CONFIDENCE: AVERAGE  
 
WITH THE LEAD SHORTWAVE CURRENTLY OVER THE NE PACIFIC OCEAN...THE  
00Z UKMET APPEARS TO BE STRONGEST WITH THE DOWNSTREAM RIDGE OVER  
WRN NOAM AND THUS PUSHES THE SHORTWAVE FURTHER NORTH THROUGH THE  
CANADIAN ROCKIES. MEANWHILE...THE 12Z NAM SHOWS THE SHORTWAVE  
ROUNDING THE RIDGE AT A SLIGHTLY LOWER LATITUDE THAN OTHER  
MODELS...AND BREAKS THROUGH THE NORTHERN PERIPHERY OF THE RIDGE  
FASTER...LEADING TO SOME TIMING DIFFERENCES DOWNSTREAM. THESE ARE  
THE LARGEST DIFFERENCES INITIALLY...AND THEREFORE NEITHER THE  
UKMET OR NAM ARE INCLUDED IN THE PREFERENCE. ADDITIONALLY...THESE  
TWO MODELS SHOW A STRONGER AND MORE AMPLIFIED SECONDARY  
WAVE...WHICH SEEMS LESS LIKELY GIVEN THE CLOSE PROXIMITY TO THE  
INITIAL WAVE (WHICH SHOULD BE QUITE STRONG ITSELF). PREFER A BLEND  
OF THE 12Z GFS...00Z ECMWF AND 00Z CMC WHICH KEEP A FLATTER  
SECONDARY WAVE AND PROVIDE AN INTERMEDIATE SOLUTION WITH THE  
PRIMARY WAVE IN HOW IT ROUNDS THE WESTERN RIDGE.  
 
   
..UPPER LEVEL LOW LINGERING NEAR THE NRN GULF OF CALIFORNIA
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 12Z GFS / 12Z NAM / 00Z ECMWF  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
THE 00Z UKMET AND 00Z CMC CONSOLIDATE AN UPPER LEVEL LOW FURTHER  
EAST IN THE VICINITY OF THE GULF OF CALIFORNIA THAN THE OTHER  
MODELS AND ENSEMBLE MEANS...AND THUS EVENTUALLY SHOW DIFFERENT  
INTERACTIONS WITH THE GRADUALLY EXPANDING TROUGH OVER THE CENTRAL  
CONUS. THE VORTICITY FIELDS ALOFT ARE STILL VERY DISPERSED IN THIS  
REGION...AND THUS THE UKMET AND CMC SOLUTIONS CANNOT BE TOTALLY  
DISCOUNTED AS UNREASONABLE POSSIBILITIES. HOWEVER...GOES  
HIGH-DENSITY WINDS IN THE 500-350MB LAYER AND LATEST WATER VAPOR  
LOOPS SHOW THE DOMINANT MID-UPPER LEVEL CIRCULATION CURRENTLY  
FURTHER WEST SO THE PREFERENCE IS TO REMAIN CLOSE TO A SOLUTION  
THAT SHOWS A SIMILAR POSITION.  
 
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML  
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML  
 
LAMERS  
 

 
 

 
 
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