646  
FXUS10 KWNH 141903  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
203 PM EST THU DEC 14 2017  
 
VALID DEC 14/1200 UTC THRU DEC 18/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z MODEL EVALUATION...WITH LATEST PREFERENCES AND CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
   
..EXITING UPPER TROUGH OVER THE NORTHEAST
 
 
...CLIPPER SHORTWAVE/LOW EXITING OFFSHORE NEW ENGLAND TODAY..  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
THE MODELS SHOW GOOD AGREEMENT WITH THE DETAILS OF THE EXITING  
LARGER SCALE TROUGH OVER THE NORTHEAST AND THE CLIPPER  
SHORTWAVE/SURFACE LOW EXITING AROUND THE BASE OF THIS TROUGH AND  
OFFSHORE NEW ENGLAND THROUGH TODAY. WILL PREFER A GENERAL MODEL  
BLEND WITH ABOVE AVERAGE CONFIDENCE.  
 
   
..SHORTWAVE DIGGING SOUTH ACROSS THE PLAINS
 
   
..ENERGY CROSSING THE LOWER MS/TN VALLEYS ON FRI
 
   
..POSSIBLE SURFACE LOW DEVELOPMENT OFF THE MID-ATLANTIC ON FRI
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-CMC CONSENSUS  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
A SHORTWAVE WILL DROP SOUTH DOWN ACROSS THE PLAINS TODAY BEFORE  
SWEEPING ACROSS THE LOWER MS AND TN VALLEY REGION ON FRIDAY. THIS  
ENERGY IS EXPECTED TO HELP RELOAD A LARGER SCALE LONGWAVE TROUGH  
ACROSS THE EASTERN U.S. BY THE END OF THE WEEK AND WILL ENCOURAGE  
A SURFACE LOW DEVELOPING OFFSHORE THE MID-ATLANTIC BY FRIDAY  
NIGHT. THE GUIDANCE SHOWS GOOD AGREEMENT OVERALL WITH THE  
SHORTWAVE DETAILS...WITH SOME MINOR TIMING DIFFERENCES.  
HOWEVER...AT THE SURFACE...THE 12Z CMC A BIT FARTHER NORTH AND A  
BIT STRONGER THAN THE REMAINING GUIDANCE AS LOW PRESSURE DEVELOPS  
OFFSHORE THE MID-ATLANTIC. GIVEN REASONABLY GOOD MODEL CLUSTERING  
SEEN OTHERWISE ALONG WITH ENSEMBLE SUPPORT...A NON-CMC CONSENSUS  
WILL BE PREFERRED.  
 
   
..NEW UPPER LOW DROPPING SOUTH TOWARD THE GREAT LAKES BY FRI
 
   
..ENERGY ADVANCING INTO NEW ENGLAND ON SAT
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-CMC CONSENSUS  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
THE MODELS TAKE ARCTIC SHORTWAVE ENERGY DROPPING SOUTH FROM  
NUNAVUT IN NORTHERN CANADA DOWN TO THE SOUTH OVER THE NEXT COUPLE  
OF DAYS WHICH RESULTS IN A NEW UPPER LOW DROPPING SOUTH OVER  
HUDSON BAY AND THEN ACROSS ONTARIO BY FRIDAY. THIS WILL RESULT IN  
HEIGHT FALLS ENCROACHING ON THE GREAT LAKES REGION AND A WAVE OF  
LOW PRESSURE IMPACTING THIS REGION. THEREAFTER GOING INTO THE  
WEEKEND...THE ENERGY WILL PIVOT ACROSS NEW ENGLAND. THE 12Z CMC  
DROPS ITS HEIGHT FALLS JUST A TAD FARTHER SOUTH WHICH RESULTS IN  
ITS SURFACE LOW DROPPING A BIT FARTHER SOUTH AS WELL COMPARED TO  
THE REMAINING GUIDANCE. THE 12Z GFS IS ALSO PERHAPS JUST A TAD  
MORE PROGRESSIVE TO SHIFT THE ENERGY FARTHER EAST INTO NEW  
ENGLAND. AT THIS STAGE...THE CMC IS A BIT MORE OF AN OUTLIER...AND  
SO A NON-CMC CONSENSUS WILL BE PREFERRED.  
 
   
..SHORTWAVE TROUGH ARRIVING ACROSS THE PACIFIC NORTHWEST ON FRI
 
   
..TROUGHING DIGGING ACROSS THE INTERMOUNTAIN WEST/PLAINS
 
   
..COLD FRONT SETTLING OVER THE PLAINS/MIDWEST BY SAT
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF THE 12Z GFS/12Z UKMET/12Z ECMWF...AT SURFACE  
BLEND OF THE 12Z UKMET AND 12Z ECMWF...ALOFT W/TROUGH  
CONFIDENCE: SLIGHTLY BELOW AVERAGE  
 
THE MODELS BREAK DOWN THE WESTERN NORTH AMERICA RIDGE BY THE END  
OF THE WEEK AND THIS ALLOWS A SHORTWAVE TROUGH AND ASSOCIATED COLD  
FRONT TO ARRIVE ACROSS THE PACIFIC NORTHWEST BY THE END OF THE  
WEEK. AS ALL OF THE ENERGY INITIALLY COMES INTO THE PACIFIC  
NORTHWEST...THE 12Z GFS IS JUST A TAD MORE PROGRESSIVE WITH THE  
ENERGY COMPARED TO THE MODEL CONSENSUS...WITH THE 12Z CMC A TAD  
SLOWER. THE REMAINING GUIDANCE IS WELL CLUSTERED AND OVERALL THE  
MODEL SPREAD WITH THE INITIAL ARRIVAL OF THE HEIGHT FALLS IS QUITE  
SMALL.  
 
ALL OF THIS ENERGY ALONG WITH A COLD FRONT WILL ADVANCE SOUTHEAST  
ACROSS THE INTERMOUNTAIN WEST AND THEN OUT ACROSS THE PLAINS AND  
MIDWEST FRIDAY NIGHT THROUGH SATURDAY. THE GUIDANCE SUPPORTS THE  
NORTHERN PORTION OF SOME OF THE UPPER TROUGHING CROSSING THE UPPER  
MIDWEST BY EARLY SATURDAY ALONG WITH A CLIPPER-STYLE SURFACE LOW.  
THE 12Z CMC IS MUCH SLOWER AND WEAKER WITH THIS SYSTEM...WITH THE  
REMAINING GUIDANCE RATHER WELL CLUSTERED. THIS ENERGY THEN DAMPENS  
OUT AS IT DIGS SOUTHEAST...BUT ALL OF THE MODELS SHOW A COLD FRONT  
ADVANCING SOUTHEAST DOWN THROUGH THE PLAINS...WITH A NEW AREA OF  
LOW PRESSURE BY LATE SATURDAY FORCING OVER THE SOUTH-CENTRAL HIGH  
PLAINS REGION. THE 12Z NAM GENERALLY KEEPS ITS ENTIRE FRONTAL ZONE  
SOUTHEAST OF THE MODEL CONSENSUS...WITH THE 12Z CMC A BIT FARTHER  
NORTH. THE 12Z GFS/12Z UKMET AND 12Z ECMWF ARE CLUSTERED IN  
BETWEEN. THE DETAILS OF LOW PRESSURE OVER THE HIGH PLAINS AND THE  
FRONTAL PLACEMENT WILL TEND TO BE RELATED TO THE DETAILS OF HEIGHT  
FALLS DROPPING SOUTH ACROSS THE INTERMOUNTAIN WEST AND INTO THE  
FOUR CORNERS REGION. THE 12Z NAM TAKES THE TROUGHING OVER THE FOUR  
CORNERS REGION A BIT FARTHER EAST COMPARED TO THE 12Z GFS AND 12Z  
UKMET...AND THE 12Z CMC AND 12Z ECMWF ARE CLUSTERED TOWARD THE  
GFS/UKMET CAMP. HOWEVER...THE GFS HAS MUCH MORE JET ENERGY DIGGING  
INTO THE BASE OF THE TROUGH COMPARED TO THE OTHER MODELS.  
ACCOUNTING FOR THE LATEST TRENDS AND OUTLIER SOLUTIONS...WPC WILL  
PREFER A BLEND OF THE UKMET/GFS AND ECMWF WITH THE FRONT/SURFACE  
LOW PLACEMENT GIVEN GOOD MODEL CLUSTERING....BUT A BLEND OF THE  
UKMET AND ECMWF WITH THE TROUGH ALOFT.  
 
   
..UPPER LEVEL LOW OVER THE BAJA PENINSULA/GULF OF CALIFORNIA
 
   
..PORTION OF ENERGY LIFTING TOWARD THE RIO GRANDE VALLEY
 
   
..ENERGY SHEARING NORTHEAST ACROSS THE LOWER MS VALLEY
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-CMC CONSENSUS  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
A WEAK SHORTWAVE DROPPING SOUTH DOWN TOWARD NORTHWEST MEXICO WILL  
MERGE UP WITH THE UPPER LOW CURRENTLY OVER THE BAJA PENINSULA  
TODAY...WITH THE RESULTANT PHASED ENERGY THEN RESULTING IN NEW  
CLOSED LOW EVOLUTION THAT MOVES EAST ACROSS WESTERN MAINLAND  
MEXICO BEFORE THEN LIFTING NORTHEAST TOWARD THE RIO GRANDE VALLEY  
ON SATURDAY IN RESPONSE TO UPSTREAM HEIGHT FALLS DROPPING INTO THE  
SOUTHWEST U.S. AND ADJACENT FOUR CORNERS REGION. ON SUNDAY...THIS  
ENERGY WILL SHEAR NORTHEAST AND DOWNSTREAM ACROSS THE SOUTHERN  
PLAINS AND LOWER MS VALLEY. THE 12Z CMC IS A STILL PERHAPS A TAD  
TOO SLOW TO EJECT THE ENERGY OUT OF MAINLAND MEXICO AND ACROSS THE  
RIO GRANDE VALLEY. THE REMAINING GUIDANCE IS WELL CLUSTERED...SO A  
NON-CMC CONSENSUS WILL BE PREFERRED.  
 
   
..UPPER LOW DEVELOPMENT OVER CALIFORNIA ON SAT
 
   
..ENERGY DIGGING TOWARD THE NORTHERN BAJA PENINSULA
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF THE 12Z UKMET AND 12Z ECMWF  
CONFIDENCE: SLIGHTLY BELOW AVERAGE  
 
THE MODELS TAKE A PORTION OF THE UPPER TROUGH CROSSING THE PACIFIC  
NORTHWEST ON FRIDAY AND DROP IT SOUTH DOWN ACROSS CALIFORNIA ON  
SATURDAY WHERE MOST OF THE MODELS SHOW IT AMPLIFYING AND  
SEPARATING OUT INTO A COMPACT CLOSED LOW THAT ARRIVES TOWARD  
SOUTHERN CALIFORNIA BY LATE SATURDAY. THE 12Z GFS IS MORE  
AGGRESSIVE IN SWINGING THE ENERGY SOUTHEAST TOWARD THE DESERT  
SOUTHWEST AND THEN EASTWARD TOWARD PARTS OF THE FOUR CORNERS  
REGION WHERE IT ATTEMPTS TO PHASE WITH ENERGY DROPPING SOUTH OVER  
THE INTERMOUNTAIN WEST. THE 12Z CMC HAS TRENDED TOWARD THE  
STRONGER GFS. THE 12Z ECMWF HAS TRENDED FARTHER EAST BUT IS NOT AS  
STRONG AS THE GFS AND CMC SOLUTIONS. THE 12Z NAM DROPS THE ENERGY  
FARTHER SOUTH AND EAST COMPARED TO THE MODEL CONSENSUS. BASED ON  
THE LATEST MODEL CLUSTERING... A BLEND OF THE 12Z UKMET AND 12Z  
ECMWF WILL BE PREFERRED. CONFIDENCE REMAINS A BIT LIMITED.  
 
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML  
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML  
 
ORRISON  
 

 
 
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