170  
FXUS10 KWNH 131635  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1134 AM EST WED DEC 13 2017  
 
VALID DEC 13/1200 UTC THRU DEC 17/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z MODEL EVALUATION...WITH LATEST PREFERENCES AND CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
   
..DEEP CYCLONE OVER THE NORTHEAST
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-UKMET CONSENSUS  
CONFIDENCE: ABOVE AVERAGE  
 
THE MODELS OVER THE NEXT 24 HOURS ALLOW THE VERY DEEP COLD  
CYCLONIC LOW OVER THE NORTHEAST TO LIFT NORTH UP ACROSS NEW  
BRUNSWICK AND THEN ACROSS EASTERN QUEBEC LATER TODAY AND TONIGHT.  
THE 00Z UKMET TENDS TO WRAP ITS SURFACE LOW PROBABLY TOO FAR BACK  
TO THE WEST OVER QUEBEC TONIGHT AND THURSDAY...AND ENDS UP LEFT OF  
THE OTHERWISE WELL CLUSTERED MODEL SUITE. WILL PREFER A NON-UKMET  
CONSENSUS AS A RESULT FOR NOW.  
 
   
..CLIPPER SHORTWAVE/LOW CENTER DIGGING SOUTHEAST FROM CANADA
 
   
..CROSSING THE UPPER MIDWEST/OH VALLEY/MID-ATLANTIC TODAY/THURS
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
THE GUIDANCE SHOWS A STRONG CLIPPER TYPE SHORTWAVE AND ASSOCIATED  
SURFACE LOW DIGGING SOUTHEAST OUT OF SOUTHERN CANADA AND QUICKLY  
MOVING SOUTHEAST TOWARD THE UPPER MIDWEST. THIS SYSTEM WILL  
RAPIDLY CROSS PARTS OF THE LOWER GREAT LAKES...OH VALLEY AND  
MID-ATLANTIC REGION TODAY THROUGH THURSDAY. THE LATEST GUIDANCE IS  
IN GOOD AGREEMENT WITH THE MASS FIELD DETAILS OF THIS SYSTEM...SO  
A GENERAL MODEL BLEND WILL BE PREFERRED.  
 
   
..SHORTWAVE DIGGING SOUTH ACROSS THE PLAINS THURS
 
   
..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 THURSDAY 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 00Z CMC REFLECTS A GENERALLY  
STRONGER AND ALSO SLOWER SURFACE LOW OFFSHORE THE MID-ATLANTIC BY  
FRIDAY NIGHT. THE REMAINING GUIDANCE IS A BIT MORE ELONGATED AND  
MODESTLY FLATTER BY COMPARISON. WILL PREFER A NON-CMC CONSENSUS  
WITH THIS SYSTEM.  
 
   
..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 CURRENTLY UP OVER 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 THE END OF THE WEEK. THIS WILL RESULT  
IN HEIGHT FALLS ENCROACHING ON THE GREAT LAKES REGION AND A WAVE  
OF LOW PRESSURE IMPACTING THIS REGION. THE 00Z CMC TENDS TO DIG  
THE ENERGY A LITTLE FARTHER SOUTH ACROSS THE GREAT LAKES REGION  
THROUGH FRIDAY BEFORE THEN CROSSING TOWARD NEW ENGLAND ON  
SATURDAY. THERE IS SOME MODEST TIMING SPREAD WITH THE TIMING OF  
THE HEIGHT FALLS WITH THE REMAINING GUIDANCE...WITH THE 12Z GFS  
AND 00Z ECMWF A TAD SLOWER THAN THE 12Z NAM AND 00Z UKMET. A  
COMPROMISE AMONG THOSE SOLUTIONS WILL BE PREFERRED...WHICH WILL  
REFLECT A NON-CMC CONSENSUS AT THIS TIME.  
 
   
..SHORTWAVE TROUGH ARRIVING ACROSS THE PACIFIC NORTHWEST ON FRI
 
   
..ENERGY DIGGING SOUTHEAST ACROSS THE INTERMOUNTAIN WEST/PLAINS
 
   
..COLD FRONT SETTLING OVER THE PLAINS/MIDWEST BY SAT
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF THE 12Z GFS AND 00Z ECMWF...AT THE SURFACE  
BLEND OF THE 12Z GFS AND 00Z UKMET...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 00Z ECMWF IS GENERALLY THE SLOWEST WITH THE  
SHORTWAVE TROUGH...WITH THE 00Z CMC AND 12Z GFS TENDING TO BE ON  
THE SLOWER SIDE OF THE GUIDANCE TOO. THE 12Z NAM IS THE MOST  
PROGRESSIVE OVERALL FOLLOWED BY THE 12Z UKMET. THE MODEL SPREAD  
WITH THE INITIAL ARRIVAL OF THE HEIGHT FALLS IS RATHER MINIMAL  
THOUGH.  
 
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. BY SATURDAY...THE 12Z NAM  
HAS ENERGY SHIFTING TOO QUICKLY OFF TO THE EAST ACROSS THE  
NORTHERN PLAINS WHICH ALLOWS THE NORTHERN PORTION OF A COLD FRONT  
AND A SURFACE WAVE TO ADVANCE MORE QUICKLY TOWARD THE UPPER MS  
VALLEY. THE REMAINING GLOBAL MODELS ARE ALL CLUSTERED TOWARD A  
SLOWER SOLUTION AND HAVE MUCH OF THE UPPER TROUGHING BACK OVER THE  
NORTHERN HIGH PLAINS AND DOWN ACROSS THE FOUR CORNERS REGION.  
HOWEVER...THE 12Z GFS IS THE SLOWEST SOLUTION WITH MUCH MORE  
ENERGY LINGERING BACK OVER THE GREAT BASIN.  
 
REGARDING THE FRONT AND A SURFACE LOW OVER THE SOUTHERN HIGH  
PLAINS ON SATURDAY...THE NAM IS FARTHEST SOUTH WITH THE  
FRONT...WITH THE CMC THE FARTHEST NORTH. THE UKMET ALSO TENDS TO  
BE A LITTLE FARTHER NORTH AND WEST WITH AT LEAST THE NORTHERN  
PORTION OF THE FRONT. THE GFS AND ECMWF SHOW MUCH BETTER  
CLUSTERING BY COMPARISON AND ARE CLOSE TO THE MODEL CONSENSUS. THE  
06Z GEFS MEAN AND 00Z ECENS MEAN SUPPORT THE MODEL CONSENSUS WITH  
THE GFS/ECMWF CLUSTER AT THE SURFACE. HOWEVER...ALOFT THE SAME  
ENSEMBLE MEANS TEND TO SUPPORT THE GFS AND UKMET SOLUTIONS.  
 
   
..UPPER LEVEL LOW OVER THE BAJA PENINSULA/GULF OF CALIFORNIA
 
   
..PORTION OF ENERGY LIFTING TOWARD THE RIO GRANDE VALLEY
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF THE 12Z GFS AND 00Z ECMWF  
CONFIDENCE: SLIGHTLY BELOW AVERAGE  
 
A WEAK SHORTWAVE DROPPING SOUTH DOWN THE SPINE OF THE ROCKIES  
TODAY WILL TEND TO MERGE UP WITH THE UPPER LOW CURRENTLY OVER THE  
BAJA PENINSULA ON THURSDAY...WITH THE RESULTANT PHASED ENERGY THEN  
RESULTING IN NEW CLOSED LOW EVOLUTION THAT DROPS SOUTHEAST ACROSS  
WESTERN MAINLAND MEXICO BEFORE THEN LIFTING NORTHEAST TOWARD THE  
RIO GRANDE VALLEY BY SATURDAY IN RESPONSE TO UPSTREAM HEIGHT FALLS  
DROPPING INTO THE SOUTHWEST U.S. AND ADJACENT FOUR CORNERS REGION.  
12Z NAM IS A FAST OUTLIER WITH THE ENERGY EJECTING TOWARD THE RIO  
GRANDE VALLEY ON SATURDAY. THE 00Z UKMET IS ALSO ON THE MORE  
PROGRESSIVE SIDE OF THE MODEL SPREAD...BUT THE 12Z GFS/00Z CMC AND  
00Z ECMWF ARE ALL SLOWER WHICH IS SUPPORTED BY THE 06Z GEFS MEAN  
AND 00Z ECENS MEAN. WILL PREFER THE SLOWER CONSENSUS FOR NOW WITH  
A BLEND OF THE GFS AND ECMWF.  
 
...UPPER LOW DEVELOPMENT OVER CALIFORNIA ON SAT..   
..ENERGY DIGGING TOWARD THE NORTHERN BAJA PENINSULA
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF THE 12Z NAM/00Z CMC AND 00Z UKMET  
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 LAT SATURDAY. THE 12Z GFS IS A STRONG  
OUTLIER WITH THIS SYSTEM. THE 12Z NAM/00Z UKMET AND 00Z CMC ALL  
ARE A BIT WEAKER BUT SHOW FAIRLY SIMILAR TIMING TO THE GFS. THE  
00Z ECMWF IS AN OUTLIER IN TAKING THE ENERGY WELL SOUTH BUT  
OFFSHORE OF CALIFORNIA. THE 06Z GEFS MEAN AND 00Z ECENS MEAN BOTH  
TEND TO FAVOR NAM/CMC AND UKMET CAMP...SO A BLEND OF THE LATTER  
WILL BE PREFERRED.  
 
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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