410  
FXUS10 KWNH 141841  
PMDHMD  
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
141 PM EST TUE NOV 14 2017  
 
VALID NOV 14/1200 UTC THRU NOV 18/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z MODEL EVALUATION INCLUDING PREFERENCES AND FORECAST CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
   
..SHORTWAVE ENTERING NORTHEAST TODAY EXITING WED
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
MODELS CONTINUE TO SHOW SOLID CONSISTENCY...SMALL VARIATIONS OF  
INITIAL SURFACE ANALYSIS WAS NOTED WITH THE 00Z UKMET BUT DOES NOT  
LEAD TO SUBSTANTIAL EVOLUTIONARY DIFFERENCES TO EXCLUDE FROM THE  
PREFERENCE (GENERAL MODEL BLEND). CONFIDENCE IS ABOVE AVERAGE.  
 
...SHORTWAVE AND ASSOCIATED SURFACE LOW CROSSING NORTHERN TIER  
TODAY INTO GREAT LAKES LATE WED...  
...TRANSITIONING SURFACE WAVE TO COASTAL LOW THROUGH GEORGES BANK  
LATE THURS/FRI...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-NAM BLEND WEIGHTED TOWARD 12Z GFS  
CONFIDENCE: AVERAGE  
 
THE 00Z CMC APPEARS TO HAVE INITIALIZED A BIT MORE WOUND UP WITH  
THE VORT CENTER AT THE APEX OF THE OVERALL ACROSS SE ALBERTA...AND  
WHILE THESE FEATURE LAGS INITIALLY...THE OVERALL TROF TIMING/SHAPE  
APPEAR TO GET BACK IN LINE WITH ACROSS THE GREAT LAKES THOUGH THE  
VORT CENTER REMAINS THE DOMINANT FEATURE WITHIN THE TROF AS A  
WHOLE LEADING TO DIFFERENCES IN LOWER LEVEL MASS FEATURES. THE  
00Z UKMET WHILE INITIALLY BETTER TIMED...IS ALSO QUITE AGGRESSIVE  
WITH THIS ONE VORT FEATURE...AND AS IT BECOMES THE BASE OF THE  
TROF THROUGH THE GREAT LAKES EARLY THURSDAY...IT GOES NEGATIVE  
TILT AND ALLOWS FOR A FASTER/DEEPER MORE WOUND UP TRANSITION OF  
THE SURFACE WAVE JUST SOUTHEAST OF NEW ENGLAND. THE 12Z NAM WHILE  
TIMED BETTER WITH THE GEFS/ECENS MEAN (SLOWER THAN THE  
UKMET)...ALSO DEPICTS A GREATER NEGATIVE TILT OF THE TROF THROUGH  
AND A MUCH FURTHER NORTH/DEEPER DEVELOPMENT OF THE SURFACE LOW IN  
THE GULF OF MAINE...TRANSITIONING INTO SE CANADA BY FRI. WHILE  
THESE SOLUTIONS REMAIN POSSIBLE... THE BULK OF ECENS MEMBERS/GEFS  
MEMBERS REPRESENTED BY THE 12Z GFS AND 00Z ECMWF ARE CLUSTERED  
WELL TO SUPPORT A 12Z GFS/00Z ECMWF BLEND AT SLIGHTLY ABOVE  
AVERAGE CONFIDENCE.  
 
19Z UPDATE: THE 12Z UKMET AND ECMWF TRENDED A BIT SLOWER WITH THE  
VORT CENTER ALLOWING FOR FURTHER SOUTH TRACK OF THE WAVE THROUGH  
THE GREAT LAKES AND INCREASED NEGATIVE TILT...LEADING TO AN  
EARLIER WOUND UP SOLUTION THAN THE GFS...BUT BOTH SLOWER AND MORE  
REASONABLE IN TIMING TO THE GFS/CMC CONFIRMING THE 12Z NAM BEING A  
BIT TOO FAST. THE CMC SHOWS A NICE SIMILARITY BETWEEN THE  
UKMET/ECMWF AND GFS SOLUTIONS. AT THIS POINT...IT IS DIFFICULT TO  
LOCK DOWN THE PRECISE TIMING OF THE VORT CENTER SWINGING THROUGH  
NEGATIVE TILT TO SPUR RAPID COASTAL CYCLOGENESIS BUT WILL CONTINUE  
TO FAVOR THE 12Z GFS BUT WILL INCLUDE SOME WEIGHT TO THE 12Z  
ECMWF/UKMET AND CMC WITHIN A NON-NAM BLEND. CONFIDENCE IS REDUCED  
DUE TO THE PREDICTABILITY IN TIMING FOR SUCH A SMALL FEATURE...BUT  
IS AVERAGE OVERALL GIVEN THE LARGER SCALE PATTERN IS AGREED UPON  
MODERATELY.  
 
...LEADING SHORTWAVE OF LONGWAVE TROUGH AXIS ALONG THE WEST COAST  
WED INTO THU...  
...NORTHERN ROCKIES LEE CYCLONE INTO SOUTHERN CANADIAN PRAIRIES BY  
FRI...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
~~~~~~~~~~~~~~  
PREFERENCE: 12Z NAM/ECMWF BLEND  
CONFIDENCE: AVERAGE TO SLIGHTLY BELOW AVERAGE  
 
LARGE CLOSED LOW OVER PACIFIC WEST OF VANCOUVER ISLAND WILL SHIFT  
SOUTHEAST AND UNFOLD BY THURSDAY SHEDDING A SHORTWAVE INTO THE  
SOUTHWEST FLOW CROSSING THE ID/MT ROCKIES. TIMING AND STRENGTH  
CONTINUE TO SHOW MODERATE SPREAD STARTING AROUND 00Z FRIDAY AS THE  
12Z GFS CONTINUES TO SHOW A SLIGHT FAST BIAS AS IT IS APT TO  
DO...THIS IS MANIFEST GREATEST ACROSS THE NORTHERN TIER INTO THE  
WESTERN GREAT LAKES LATE FRI PRESSING THE COLD FRONT A BIT TOO FAR  
EAST. THE 00Z ECMWF SHOWS ITS BIAS AS WELL EVOLVING A BIT SLOWER  
AND WEAKER...LEADING TO A SURFACE WAVE TO DEVELOP FURTHER SOUTH  
WITHIN THE ENSEMBLE CLUSTER. AS THE WAVE EXITS INTO THE NORTHERN  
GREAT PLAINS/SOUTHERN CANADIAN PRAIRIES THE SHAPE/TIMING OF THE  
FRONT LOOK FAVORABLE TO THE GFS BUT STILL LAG OVERALL. THE 00Z  
UKMET WHILE IS MOST CENTRALLY TIMED FINDS A NICE UPPER FLOW REGIME  
TO AMPLIFY THE WAVE/WIND UP CYCLONE A BIT TOO AGGRESSIVELY THROUGH  
S CANADA...THOUGH THE SHAPE/TIMING OF THE WAVE ACTUALLY LOOK QUITE  
GOOD TO CONSIDER SOME LOW WEIGHTING TO IT. THE 00Z CMC HAS A  
ECMWF FEEL BUT ALSO SLOWER AND MORE WOUND UP INTO N MANITOBA BY  
00Z SAT...FOR LITTLE TO NO CONSIDERATION. THIS LEAVES THE 12Z NAM  
WHICH LIKE THE UKMET LOOKS MOST REASONABLE IN TIMING/SHAPE WITH  
RESPECT TO THE ENSEMBLE MEAN...THOUGH MAY BE DEVELOPING THE  
PIVOT/FULCRUM CYCLONE ACROSS BOREAL SASKATCHEWAN/MANITOBA A BIT  
TOO DEEPLY...LEADING TO A SURFACE WAVE ON THE NORTHERN FRINGE OF  
THE ENSEMBLE SFC LOW CLUSTER. STILL ITS CONNECTION THROUGH THE  
TROF INTO THE CENTRAL ROCKIES (SEE SECTION BELOW) ALSO MAKES IT A  
BIT MORE FAVORABLE OVERALL. AS SUCH A BLEND OF THE 12Z NAM/00Z  
ECMWF/UKMET IS WPC PREFERENCE THOUGH WEIGHTED THE MAJORITY TO THE  
NAM (~70%). CONFIDENCE IS AVERAGE TO SLIGHTLY BELOW AVERAGE IN  
THIS BLEND.  
 
19Z UPDATE: THE 12Z UKMET SHOWS LITTLE CHANGE FROM THE 00Z RUN  
STILL A BIT MORE WOUND UP/DEEPER BUT HAVING A GOOD TIMING/TO THE  
LOW/FRONTAL ZONE. THE 12Z ECMWF SHOWS A BIT GREATER STRENGTH TO  
THE WAVE AND THEREFORE SPINS UP A DEEPER AND FURTHER NORTH SURFACE  
SOLUTION QUITE FAVORABLE TO INITIAL PREFERENCE/THINKING. THE 12Z  
GEFS ALSO SUPPORTS THIS ECMWF SOLUTION PROVIDING GREATER  
CONFIDENCE IN A 12Z NAM/ECMWF BLEND AT EQUAL PARTS. CONFIDENCE  
REMAINS THE SAME...AVERAGE TO SLIGHTLY BELOW AVERAGE.  
 
...TRAILING/MAIN LONGWAVE TROUGH PROGRESSING ACROSS THE WEST COAST  
ON THURSDAY AND GREAT BASIN/CENTRAL ROCKIES FRI...ASSOCIATED  
CENTRAL PLAINS LEE CYCLONE/FRONTAL ZONE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
~~~~~~~~~~~~~~  
PREFERENCE: 12Z NAM/ECMWF/CMC BLEND  
CONFIDENCE: SLIGHTLY BELOW AVERAGE  
 
THE ECENS MEAN HAS BEEN QUITE CONSISTENT WITH THE SLOWER TROF AXIS  
PROGRESSING INTO THE WEST COAST BY EARLY TO MIDDAY FRIDAY THOUGH  
REMAINS ON THE SLOWER SIDE OF THE OVERALL ENSEMBLE SUITE...THE 00Z  
ECMWF HOWEVER IS EVEN ON THE ECENS MEMBER EXTREME WITH A  
DEEPER/MUCH SLOWER SHARPER WAVE ENTERING CA...THIS MAY BE IN PART  
DUE TO A STRONGER SUBTROPICAL JET IN ADVANCE OF THE WAVE ALLOWING  
FOR SLIGHTLY ENHANCED SHORTWAVE RIDGING AND DELAYING EASTWARD  
PROGRESSION...UPSTREAM FASTER AND DEEPER WAVE ALSO HELPS TO  
FLATTEN THE RIDGE BETWEEN...WHICH SEEMS UNREALISTIC BUT ALSO SHOWS  
GREAT VARIATION IN THE ECENS MEMBERS TO PROVIDE LOW CONFIDENCE.  
THE 12Z GFS LIKELY DUE TO A SLIGHTLY STRONGER POLAR JET ACROSS THE  
NORTHERN ROCKIES...HAS SLOWED THE EASTWARD PROGRESSION OF THE BASE  
OF THE TROF MORE FAVORABLY WITH THE OVERALL TREND/ECENS  
MEAN...THOUGH THE OVERALL TROF ORIENTATION IS MUCH MORE POSITIVE  
WHICH LEADS TO A FASTER/EASTWARD SURFACE PATTERN THAT STICKS OUT  
WITHIN THE OVERALL GUIDANCE SUITE TO NOT PREFER IT AT THIS  
TIME...THOUGH IT IS TRENDING BETTER. THE 12Z NAM SHOWS THE  
GREATEST COMPARISON IN SHAPE/TIMING/DEPTH WITH THE ECENS  
MEAN/OVERALL MEAN TREND...TO PREFER IT. ISSUES WITH THE DEEPER  
00Z UKMET FURTHER NORTH DO NOT SEEM TO PLAY AS MUCH OF A FACTOR IN  
THE TRAILING BASE TO ALSO LOOK QUITE SIMILAR AND PREFERABLE. AS  
SUCH A 12Z NAM/00Z UKMET BLEND IS PREFERRED FOR THIS PORTION OF  
THE WAVE. THE SPREAD REMAINS GREAT AND WITH INFLUENTIAL PIECES OF  
ENERGY EMERGING FROM DATA POOR REGIONS...CONFIDENCE IN THIS BLEND  
MAINTAINING IS QUITE LOW. EVEN THOUGH THERE IS CONFIDENCE IN THIS  
BLEND GIVEN THE DATA...THE PATTERN LEADS TO BELOW AVERAGE  
CONFIDENCE OVERALL.  
 
19Z UPDATE: THE 12Z ECMWF REMAINS A BIT MORE AMPLIFIED THAN THE  
BULK OF 00Z ECENS MEMBERS BUT HAS TRENDED A BIT FASTER AND LESS  
DEEP/SOUTH...THIS KEEPS IT SLIGHTLY SLOWER THAN THE INITIAL  
PREFERENCE/12Z NAM. THE 00Z UKMET HAS SIGNIFICANTLY SLOWED THE  
EASTWARD PROGRESSION OF THE BASE OF THE TROF THROUGH THE GREAT  
BASIN AND IS MUCH SHARPER OVERALL AND TAKING ON A MORE POSITIVE  
OVERALL TILT...MATCHING THE 12Z GFS. THE 12Z CMC HAS TRENDED A  
BIT DEEPER AND AS SUCH IS A BIT SLOWER SHOWING A SUGGESTION OF THE  
SLOWER ECMWF SOLUTION AND APPEARS A GOOD MIDDLE GROUND BETWEEN THE  
NAM/ECMWF. AS SUCH WILL CONTINUE TO FAVOR THE 12Z NAM AND  
INCLUDED THE 12Z ECMWF/CMC AT LOWER WEIGHTS WITHIN THE BLEND  
(50/25/25) TO NEAR THE 00Z ECENS MEAN AS BEST AS POSSIBLE.  
CONFIDENCE IS RAISED SLIGHTLY GIVEN AN OVERALL TREND TOWARD  
COMPROMISE FROM GFS/UKMET TO ECMWF/CMC. STILL THE  
PREDICTABILITY/SPREAD IS LOW/LARGE ENOUGH TO HAVE SLIGHTLY BELOW  
AVERAGE CONFIDENCE OVERALL.  
 
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