786  
FXUS10 KWNH 150512  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1211 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 PRELIMINARY 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 GFS / 12Z ECMWF / 12Z UKMET  
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.  
 
...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 / 12Z 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.  
 
...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 / 12Z ECMWF / 12Z 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.  
 
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