119  
FXUS10 KWNH 150632  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
131 AM EST WED NOV 15 2017  
 
VALID NOV 15/0000 UTC THRU NOV 18/1200 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
00Z MODEL EVALUATION WITH FINAL PREFERENCES AND CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
...SHORTWAVE AND ASSOCIATED SURFACE LOW CROSSING GREAT LAKES AND  
NORTHEAST TODAY AND TONIGHT...  
...TRANSITIONING SURFACE WAVE TO COASTAL LOW THROUGH GEORGES BANK  
LATE ON THURSDAY AND INTO FRIDAY...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF THE 00Z ECMWF / 00Z GFS / 00Z CMC  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
THE PRIMARY DIFFERENCES WITH THIS SYSTEM APPEAR TO BE PRIMARILY  
RELATED TO THE TIMING OF THE WAVE AS IT REACHES THE ATLANTIC  
COAST...AND HOW THAT AFFECTS THE COASTAL CYCLOGENESIS. THE 00Z NAM  
HAS A FASTER APPROACH OF THE WAVE TO THE COAST...SHOWING THE  
SURFACE LOW DEVELOPING QUICKER THAN OTHER MODELS. STRONGER INITIAL  
CYCLOGENESIS MAY LEAD TO CHANGES IN IMPACTS ALONG THE SOUTHERN NEW  
ENGLAND COAST...BUT THIS SOLUTION IS NOT FAVORED AT THIS TIME AS  
IT IS FASTER THAN OTHER MODELS AND THE ENSEMBLE MEANS. THE 12Z  
CMC...BY CONTRAST...IS A SLIGHTLY SLOWER WITH THE SHORTWAVE AND ON  
THE WEAKER END OF AVAILABLE MODELS. THIS ALSO DEVIATES FROM THE  
ENSEMBLE MEANS IN A MORE SUBSTANTIAL WAY THAN THE OTHER GLOBAL  
MODELS. THE 00Z GFS ALONG WITH THE 12Z UKMET AND ECMWF ARE QUITE  
CLOSE IN THEIR DEPICTION OF THIS SYSTEM. THERE ARE SOME DETAIL  
DIFFERENCES...BUT THESE ARE NOT SIGNIFICANT ENOUGH TO EXCLUDE ANY  
ONE MODEL...SO A BLEND OF THESE THREE MODELS IS PREFERRED.  
 
06Z UPDATE: CHANGE TO ADD THE CMC AND EXCLUDE THE UKMET FROM THE  
PREFERENCE. THE 00Z CMC LOOKS TO BE IN MUCH BETTER AGREEMENT WITH  
THE OTHER GLOBAL MODELS ON THE STRENGTH AND TIMING OF THE  
SHORTWAVE SO IT IS NOW INCLUDED IN THE FINAL PREFERENCE. THE 00Z  
UKMET IS CONSIDERABLY DEEPER WITH ITS SURFACE LOW BY 17/00Z AND ON  
THURSDAY NIGHT IS GENERALLY ABOUT 5-6MB DEEPER THAN ITS PREVIOUS  
RUN. THE SURFACE LOW IS EVEN DEEPER THAN SUGGESTED BY THE  
PREVIOUSLY MOST AGGRESSIVE NAM SOLUTION...AND THIS MAKES THE UKMET  
AN OUTLIER. THE NAM AND UKMET CAN SHOW STRONGER CYCLONES AT  
TIMES...THUS WITHOUT ADDITIONAL MODEL SUPPORT THE PREFERENCE IS  
FOR THE MORE CONSISTENT GFS/ECMWF SOLUTION (WHICH THE CMC IS NOW  
IN AGREEMENT WITH).  
 
...LEAD SHORTWAVE KICKING AHEAD OF THE PRIMARY LONGWAVE TROUGH IN  
THE WEST...THROUGH THE NORTHERN ROCKIES AND INTO SOUTHERN CANADA...   
..LEE CYCLOGENESIS IN THE CANADIAN PRAIRIES LATE THU/FRI
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF THE 00Z GFS / 00Z NAM / 00Z ECMWF  
CONFIDENCE: AVERAGE TO SLIGHTLY BELOW AVERAGE  
 
MODELS HAVE MOVED INTO BETTER AGREEMENT WITH THIS SYSTEM  
OVERALL...WITH A TIGHT CLUSTERING OF SURFACE LOW POSITIONS AND  
INTENSITIES OVER SOUTH-CENTRAL CANADA BY THURSDAY NIGHT. WITH THE  
EXCEPTION OF THE 12Z CMC AND 12Z UKMET...THE MODELS ARE GENERALLY  
ALL WITHIN 100-150MI (POSITION) AND 2 MILLIBARS (INTENSITY) OF  
EACH OTHER AT 17/06Z. THE 12Z CMC IS MUCH WEAKER WITH ITS  
DEPICTION OF THE SHORTWAVE...WHICH DOES NOT SEEM TO MATCH THE  
VIGOR OF THE TROUGH CURRENTLY APPROACHING THE WEST COAST. ALTHOUGH  
THE EMBEDDED SHORTWAVES CAN VARY QUITE A BIT IN INTENSITY...THE  
CURRENT TRENDS COUPLED WITH MODEL AGREEMENT THAT IS DIFFERENT THAN  
THE CMC MEAN IT IS EXCLUDED FROM THE PREFERENCE FOR THIS SYSTEM.  
THE 12Z UKMET IS NOT VERY DIFFERENT ON POSITION OF THE SURFACE  
LOW...BUT ITS DEEPENING RATE FAR EXCEEDS THAT OF OTHER MODELS (984  
MB AT 17/12Z VERSUS 992MB AVERAGE OF THE OTHER MODELS). ALTHOUGH  
THE SHORTWAVE SHOULD BE STRONGER THAN WHAT THE CMC IS  
PROJECTING...ITS LOW AMPLITUDE AND LACK OF SIGNIFICANT BAROCLINIC  
FORCING ARGUE AGAINST SUCH A RAPID DEEPENING RATE. THEREFORE...THE  
PREFERENCE IS FOR A BLEND OF THE 00Z GFS AND NAM...AND 12Z ECMWF.  
 
06Z UPDATE: NO CHANGE FROM PRELIMINARY PREFERENCE. THE 00Z CMC AND  
00Z UKMET CONTINUED TO SHOW DIFFERENCES SIMILAR TO THE 12Z MODEL  
CYCLE.  
 
...TRAILING/MAIN LONGWAVE TROUGH PROGRESSING THROUGH THE WESTERN  
STATES THROUGH FRIDAY NIGHT...   
..TROUGH REACHING THE PLAINS FRIDAY NIGHT AND SATURDAY
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF 00Z NAM / 00Z ECMWF / 00Z CMC / 12Z EC ENS  
CONFIDENCE: SLIGHTLY BELOW AVERAGE  
 
THE 12Z ENSEMBLE SPAGHETTI PLOTS REVEALED A NOTABLE SPLIT IN  
MODELS WITH THEIR DEPICTION OF THIS TROUGH. THE 12Z  
GFS...GEFS...CMC ENS MEAN...AND MAJORITY OF CMC AND GEFS ENSEMBLE  
MEMBERS...SHOWED A MORE PROGRESSIVE AND LESS AMPLIFIED TROUGH.  
HOWEVER THE 12Z ECMWF...EC ENS MEAN...UKMET...OPERATIONAL  
CMC...AND MAJORITY OF EC ENS MEMBERS SHOWED A MORE AMPLIFIED  
TROUGH WITH A SLOWER PROGRESSION THROUGH THE WEST. THERE WAS VERY  
LITTLE OVERLAP BETWEEN THE TWO CAMPS.  
 
HOWEVER...BOTH 00Z RUNS OF THE GFS AND NAM HAVE TRENDED SLOWER  
THAN THEIR PAST TWO MODEL CYCLES (14/12Z AND 14/00Z)...WHICH  
SUGGESTS A HIGHER CONFIDENCE IN THE SLOWER AND MORE AMPLIFIED  
SOLUTION ADVERTISED BY THE ECMWF. HOWEVER...THE 00Z GFS REMAINS A  
LITTLE FASTER. WILL MAINTAIN THE PREFERENCE OF THE PREVIOUS MODEL  
CYCLE FOR NOW...GIVEN THAT IT SEEMS THE ECMWF MAY BE LEADING THE  
TREND. THE 12Z UKMET IS ALSO CLOSE TO THE TIMING OF THE  
TROUGH...BUT SHOWS MUCH MORE AMPLIFIED UPSTREAM RIDGING...SO FOR  
NOW IT WILL CONTINUE TO BE EXCLUDED.  
 
06Z UPDATE: NO CHANGE FROM PRELIMINARY PREFERENCE. THE 00Z  
NAM...00Z ECMWF...AND 00Z CMC CONTINUE TO BE IN GOOD AGREEMENT AND  
ACTUALLY HAVE MOVED INTO BETTER AGREEMENT AS COMPARED TO THE 12Z  
MODEL CYCLE. THE 00Z UKMET IS VERY CLOSE TO THE 00Z GFS...
BUT  
GIVEN THE NOTEWORTHY TREND OF THE GFS CLOSER TO THE ECMWF...THE  
PREFERENCE WILL REMAIN UNCHANGED.  
 
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