861  
FXUS10 KWNH 151851  
PMDHMD  
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
150 PM EST WED NOV 15 2017  
 
VALID NOV 15/1200 UTC THRU NOV 19/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z MODEL EVALUATION WITH PREFERENCES AND CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
...SHORTWAVE AND ASSOCIATED SURFACE LOW CROSSING GREAT LAKES AND  
NORTHEAST TODAY...  
...TRANSITIONING SURFACE WAVE TO COASTAL LOW LATE ON THURSDAY AND  
INTO FRIDAY...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
MODELS ARE CONSOLIDATING ON A COMMON SOLUTION WITH THE LONE  
REMAINING DIFFERENCE SEEN OVER THE LAST FEW RUNS...THAT BEING THE  
TIMING/DEPTH AND LOCATION OF THE COASTAL CYCLOGENESIS. RECENT  
RUNS SHOW EXPECTED SMALL DIFFERENCES/VARIANCE FOR THE LOW TO  
DEVELOP SOUTH OF RI AND INTO THE GULF OF MAINE. THE 00Z UKMET IN  
ITS KNOWN BIAS IS A BIT DEEPER AND PREFERS A STRONG WOBBLE/EARLIER  
OCCLUSION...TUCKING IT CLOSEST TO DOWNEAST ME ALONG WITH THE 12Z  
NAM (WHICH IS ALSO A BIT DEEPER- TYPICAL OF ITS BIAS). THIS  
WOBBLE WILL SLOW ITS NORTHEASTWARD TREK COMPARED TO THE OVERALL  
GUIDANCE SUITE. THE GFS WAS A BIT WEAK IN THE CENTER THEREFORE  
SHIFTING THE SURFACE WAVE TO THE CENTRAL/SOUTHERN SIDE OF THE  
ENSEMBLE CLUSTER...HOWEVER THE 12Z RUN HAS TRENDED MORE IN LINE  
WITH THE STRONGER INNER CORE AND NOW MATCHES EVEN TIGHTER WITH THE  
ECMWF/CMC/NAM SOLUTIONS. ALL CONSIDERED A NON-UKMET BLEND IS  
SUPPORTED AT SLIGHTLY ABOVE AVERAGE CONFIDENCE.  
 
19Z UPDATE: THE 12Z UKMET SHIFTED A BIT MORE POSITIVELY TOWARD THE  
OVERALL CONSENSUS...AND WHILE THE 12Z CMC/ECMWF SHIFTED A TAD BIT  
FASTER IT MATCHES THE GFS QUICK WELL TO SUPPORT A GENERAL MODEL  
BLEND AT ABOVE AVERAGE CONFIDENCE.  
 
...LEAD SHORTWAVE KICKING AHEAD OF THE PRIMARY LONGWAVE TROUGH IN  
THE WEST...THROUGH THE NORTHERN ROCKIES AND INTO SOUTHERN CANADA  
WITH LEE CYCLOGENESIS INTO THE CANADIAN PRAIRIES LATE THU/SAT ...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-NAM BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
CLUSTERING CONTINUES TO TIGHTEN NOW AS THE SHORTWAVE STARTS TO  
EMERGE FROM THE LARGER PARENT DEEP CYCLONE OFF THE NW COAST. THE  
12Z NAM CONTINUES TO TRACK THE SYSTEM A BIT FURTHER NORTH THAN THE  
REMAINING SOLUTIONS AND FAVORS SPLITTING THE WAVE TO THE NORTH  
INTO CANADA WHILE PRESSING THE SOUTHERN PORTION OF THE WAVE  
THROUGH THE NORTHERN TIER INTO THE NORTHERN GREAT LAKES BY SAT  
MUCH FASTER AND STRONGER THAN THE OTHER GUIDANCE (AFFECTING THE  
SOUTHERN PORTION OF THE MEAN TROF LIFTING FROM THE CENTRAL MS  
VALLEY...SEE SECTION BELOW)...MAKING THE NAM LESS PREFERABLE  
ESPECIALLY AFTER 00Z/SAT. THE 12Z GFS WHILE REMAINING SLIGHTLY  
FASTER THAN THE GEFS MEAN SEEMS TO HAVE TEMPERED THE  
STRENGTH/CYCLONIC SPIN-UP OF THE WAVE INTO CANADA RELATIVE TO THE  
00Z/06Z RUNS SLOWING ITS NORTHEASTWARD PUSH RELATIVE TO THOSE  
EARLIER RUNS. THIS PAIRED WITH A MUCH STRONGER/FASTER SOLUTION  
PRESENTED BY THE 00Z ECMWF SEEM TO MATCH WELL TO REPRESENT THE  
GEFS/ECENS MEANS (THAT SIT DIRECTLY BETWEEN THEIR OPERATIONAL  
COUNTERPARTS. THE 00Z UKMET CONTINUES TO BE SLIGHTLY NORTH (LIKE  
THE NAM) THOUGH MORE IMPORTANTLY WRAPS UP A DEEPER IN DEPTH AND  
STRENGTH THOUGH TIMING IS MATCHED OK WITH THE ECMWF. THE 00Z CMC  
IS MUCH SLOWER AND LIKE THE UKMET MORE AMPLIFIED BEING THE MOST  
OUTSIDE FRINGE OF THE MAIN DETERMINISTIC GUIDANCE MEMBERS. AS  
SUCH A 00Z ECMWF/12Z GFS BLEND IS SUPPORTED BUT EVOLUTION LOOKS  
REALISTIC AND REPRESENTATIVE OF THE PATTERN/ENSEMBLE SUITE TO HAVE  
SLIGHTLY ABOVE AVERAGE CONFIDENCE IN THIS THIS BLEND.  
 
19Z UPDATE: THE 12Z UKMET TRENDED A BIT FASTER AND LESS  
AMPLIFIED/WOUND UP. ADDITIONALLY THE 12Z CMC WAS LESS AMPLIFIED  
AND FASTER ALONG WITH SLIGHTLY FASTER 12Z ECMWF RESULTING IN  
FAIRLY GOOD AGREEMENT WITH RESPECT TO THE 12Z GFS. THIS LEAVES  
THE 12Z NAM AS THE LONE OUTLIER. AND WHILE THE ECMWF IS FAVORED  
SLIGHTLY IN THE OVERALL WEIGHTING IN THE PREFERENCE...A NON-NAM  
BLEND IS SUPPORTED AT SLIGHTLY ABOVE AVERAGE CONFIDENCE.  
 
...TRAILING/MAIN LONGWAVE TROUGH PROGRESSING THROUGH THE WESTERN  
STATES FRI NIGHT REACHING THE PLAINS/MIDWEST THRU SAT WITH  
ASSOCIATED SURFACE WAVE FROM E CO FRI NIGHT TO CENTRAL GREAT LAKES  
SAT...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 12Z ECMWF/CMC (75%) WITH 12Z GFS (25%)  
CONFIDENCE: AVERAGE  
 
LAST 4 CYCLES OF THE ENSEMBLE SPAGHETTI PLOTS REVEALS A LARGE  
CHANGE WITH THE 00Z ECENS MEMBERS/MEAN ADJUSTING MUCH FASTER WITH  
GREATER AMPLIFICATION OF THE UPSTREAM RIDGE AND SLIGHTLY BROADER  
TROF SHIFTING INTO THE THE EASTERN THIRD OF THE US BY LATE  
SAT...WHILE THE OTHER GUIDANCE (CMCE/GEFS/SREF AND THEIR  
OPERATIONAL MEMBERS) CONTINUE TO BE MUCH MORE AMPLIFIED ON BOTH  
FEATURES AS WELL AS SLIGHTLY FASTER. OVERALL THIS SHIFT WAS A  
POSITIVE SIGN; IN GENERAL WHEN THE ECMWF/ECENS MEAN DOES THIS  
TOWARD A FASTER SOLUTION...THIS ADJUSTMENT OCCURS AND THEN BECOMES  
STABLE WITH OTHER GUIDANCE ADJUSTING TOWARD IT (ESPECIALLY AS  
FEATURES EMERGE OUT OF COMBINING STREAMS IN THE EASTERN PACIFIC).  
THE OVERALL SHAPE/TIMING AND STRENGTH OF THE 00Z ECMWF SEEMS A  
VERY STRONG REPRESENTATIVE OF THE ECENS MEAN AND SEEMS TO BE THE  
BAR TO ADJUST TO/FROM. THE 00Z UKMET IS A CLEAR  
OUTLIER...PRESENTING A BROADER AND SLOWER TROF EVOLUTION ACROSS  
THE CENTRAL PLAINS AS THE SURFACE WAVE CLEARLY LAGS AS A WHOLE.  
THIS SEEMS DRIVEN BY THE UPSTREAM JET STREAK BEING MUCH WEAKER OR  
NOT EVEN OVER-TOPPING THE RIDGE IN THE WEST TO HELP NARROW THE  
WAVELENGTH OF THE TROF AS A WHOLE. THE 00Z CMC TRENDS NICELY WITH  
THE ECMWF INITIALLY ESPECIALLY EMERGING FROM THE PACIFIC THROUGH  
THE MOUNTAINS; HOWEVER...NORTHERN STREAM ENERGY DESCENDS ACROSS  
THE DAKOTAS SAT MUCH TOO FAR SOUTH AND SUPPORTING CYCLONIC  
AMPLIFICATION WHICH DELAYS THE SURFACE LOW AND KEEPS IT SOUTH.  
 
AS MENTIONED IN THE SECTION ABOVE...THE 12Z NAM IS QUICK TO SPLIT  
THE NORTHERN STREAM WAVE (BISECTING JET IN S CANADA) THAT LEADS TO  
A STRONGER/FASTER HEIGHT FALL COUPLET TRACKING THROUGH THE GREAT  
LAKES. WHILE THE SOUTHERN PORTION OF THE LARGER SCALE WAVE IS  
QUITE FAVORABLE COMPARATIVE TO THE ECENS MEAN/00Z ECMWF...THE  
INTERACTION OF THE DEEPER WAVE ACROSS THE GREAT LAKES LEADS TO  
UNREPRESENTATIVE NORTHERN/FASTER DEVELOPMENT OF THE WAVE THROUGH  
SAT...GENERALLY UNFAVORABLE AT THIS POINT. THE 12Z GFS APPEARS TO  
SHOW THE FIRST SIGNS OF THE ADJUSTMENT TOWARD THE NEW ECMWF/ECENS  
MEAN POSITION...HAVING SLOWED A BIT. WHILE THE JET STREAK THAT  
DEVELOPS OVER THE NORTHERN ROCKIES FRI/SAT CONTINUES TO SUPPORT A  
FAST TRANSITION ACROSS ACROSS THE MO RIVER VALLEY INTO THE  
SOUTHERN GREAT LAKES...THERE IS SOME CONFIDENCE IN ITS INCLUSION  
TO THE BLEND. AS SUCH A 2/3RD 00Z ECMWF AND 1/3 GFS BLEND IS  
SUPPORTED (THOUGH BLENDING SOME 12Z NAM WOULD BE USEFUL THROUGH  
THE SOUTHERN ROCKIES/PLAINS THURS/FRI). CONFIDENCE IS INCREASED  
BY THE AFOREMENTIONED ADJUSTMENTS TOWARD A COMMON SOLUTION TO HAVE  
AVERAGE TO SLIGHTLY ABOVE AVERAGE CONFIDENCE IN THIS BLEND.  
 
19Z UPDATE: THERE WAS LITTLE CHANGE NOTED BETWEEN THE 12Z ECMWF  
AND THE 00Z RUN PERHAPS A TAD SLOWER OVERALL BUT PRESSING THE COLD  
FRONT FASTER THROUGH THE SOUTHERN STATES SAT. THE 12Z CMC JOINED  
THE ECMWF WITH SIGNIFICANT REDUCTION OF NORTHERN STREAM INFLUENCE  
ACROSS THE MIDWEST ON SAT. THE 12Z UKMET ALSO TRENDED POSITIVELY  
TOWARD THE GROWING CONSENSUS IN TIMING BUT LIKE THE 00Z RUN  
REMAINS A BIT BROADER WITH THE TROF DELAYING IT SUFFICIENTLY TO  
NOT WANT TO INCLUDE IT IN THE BLEND. ALL CONSIDERED WILL SUPPORT A  
12Z ECMWF/CMC BLEND WITH A DASH OF THE 12Z GFS (25%) WITH  
CONFIDENCE TRENDING TO THE POSITIVE SIDE OF AVERAGE CONFIDENCE.  
 
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