180  
FXUS10 KWNH 260644  
PMDHMD  
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
244 AM EDT THU OCT 26 2017  
 
VALID OCT 26/0000 UTC THRU OCT 29/1200 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
00Z MODEL EVALUATION INCLUDING PREFERENCES AND CONFIDENCE INTERVALS  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
...INCREASINGLY NEGATIVE TILT SHORTWAVE TROUGH EJECTING INTO THE  
NORTHEAST AND THEN DEAMPLIFYING OVER EASTERN CANADA WITH SECONDARY  
SURFACE LOW DEVELOPMENT NEAR THE GULF OF MAINE...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 00Z GFS/ECMWF BLEND  
CONFIDENCE: AVERAGE  
 
THE 00Z NAM LIKE THE 18Z NAM SHOWS CONTINUES A STRONGER TREND AT  
THE APPROPRIATE TIME IN THE NEGATIVE TILT TROF EVOLUTION NEAR CAPE  
CODE AT 24HRS...THIS DEEPER EVOLUTION ALLOWS FOR THE CYCLONE (THRU  
THE ENTIRE DEPTH) TO SLOW AS WELL LEADING TO THE NAM BREAKING FROM  
THE OTHERWISE TIGHT GUIDANCE. NORMALLY THIS WOULD LEAD TO THE NAM  
BEING ELIMINATED FROM THE PREFERENCE...HOWEVER THIS TREND TOWARD  
DEEPENING ON DAY 1 HAS BEEN POSITIVE IN VERIFICATION EVEN WHEN  
OTHER GUIDANCE REMAINS CONSISTENT. AS SUCH THERE IS PAUSE FOR ITS  
FULL EXCLUSION. IN THIS SIMILAR VAIN...THE 12Z UKMET IS STRONG AS  
WELL BUT IS MUCH FASTER THAN EVEN THE ECMWF/CMC/ENSEMBLE SUITE  
TRENDING AGAINST METEOROLOGICAL EVOLUTION/EXPECTATIONS. THE 00Z  
GFS REMAINED SIMILAR TO PRIOR 12Z/18Z RUNS AS WELL AS THE 12Z  
ECMWF/CMC AND THE ENSEMBLES. AS SUCH WILL PREFER A NON-UKMET  
BLEND WEIGHTING TOWARD ECMWF/GFS/CMC THOUGH NOT IGNORING THE 00Z  
NAM. GIVEN THIS NAM TREND CONFIDENCE IS REDUCED A BIT TO AVERAGE.  
 
07Z UPDATE: THE 00Z ECMWF SHIFTED A BIT FASTER THE THE 12Z RUN AS  
WELL AS FASTER THAN THE 00Z GFS. THIS LEADS TO FURTHER SEPARATION  
FROM THE SLOWER DEEPER NAM...SUGGESTING INITIAL THOUGHTS ABOUT THE  
NAM MAY BE FRUITLESS; HOWEVER THE 00Z CMC IS A BIT SLOWER JUST NOT  
AS DEEP/SLOW AS THE NAM. THE 00Z UKMET IS QUITE  
SIMILAR...INITIALLY FAST BUT STRONG...LEADING IT TO SLOW  
COMPARATIVELY TO THE GFS/ECMWF. AS SUCH A GFS/ECMWF BLEND MAY BE  
THE BEST AVENUE GIVEN CONSISTENCY AS WELL AS MATCH TO THE FAIRLY  
TIGHT ENSEMBLE SUITE (INCLUDING THE 00Z GEFS MEMBERS). CONFIDENCE  
REMAINS AVERAGE IN THIS BLEND.  
 
 
...SHORTWAVE TROUGH DIGGING INTO THE WESTERN GREAT LAKES BY FRIDAY  
WITH ASSOCIATED SURFACE CYCLONE DEVELOPMENT...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
GOES-WV MOSAIC DEPICTS HIGHLY ENERGETIC SHORTWAVE ACROSS SOUTH  
CENTRAL CANADA AT THIS TIME AND IS CLEARLY EXPECTED TO BECOME A  
CLOSED UPPER LOW LATER TODAY IN THE UPPER MS VALLEY. GUIDANCE IS  
QUITE SIMILAR THROUGH EARLY FRIDAY WHEN THE SLIGHTLY COLDER 12Z  
CMC BREAKS FROM THE CLUSTER WITH ENHANCED COLD AIR ADVECTION  
DROPPING THE LOW FURTHER SOUTH ACROSS THE MIDWEST LENDING TOWARD  
ITS EXCLUSION FROM ANY BLEND THEREAFTER. BY 72HRS...THE WAVE HAS  
BECOME QUITE MERIDIONAL EXTENDING FROM CENTRAL ONTARIO THROUGH THE  
THE LOWER MS VALLEY...AFTER THIS TIME INTERNAL WAVE  
TIMING/AMPLIFICATIONS ARE SLIGHTLY DISPLACED BASED ON MESOSCALE  
FEEDBACK. NO ONE MODEL SOLUTION WILL BE CORRECT IN HANDLING THESE  
INDIVIDUAL FEATURES TO HAVE MUCH CONFIDENCE OVERALL...SO A BLEND  
OF THE REMAINING GUIDANCE SEEMS PRUDENT TO BEST ACCOUNT FOR THE  
SMALLER SCALE VARIATIONS. THE 00Z GFS WAS A GOOD EXAMPLE OF THIS  
RUN TO RUN VARIATION AS IT TRENDED A BIT FASTER WITH THE TROF  
ROTATING THROUGH THE MIDDLE OF THE WAVE ACROSS THE CENTRAL  
APPALACHIANS; MAKING A NORTHWARD SHIFT ACROSS PA/CENTRAL NY VERSUS  
FURTHER SOUTH PA/WV. ALL CONSIDERED A NON-CMC BLEND IS SUPPORTED  
AT AVERAGE CONFIDENCE.  
 
07Z UPDATE: THE 00Z CMC RESOLVED THE COLDER/FURTHER SOUTH SOLUTION  
THROUGH DAY 2...AND MATCH NICELY TO THE GFS/ECMWF/UKMET/NAM  
THROUGH THIS POINT. THE 00Z ECMWF AND UKMET BOTH TRENDED A BIT  
FASTER IN LIFTING NORTHWARD THROUGH THE CENTRAL PORTION OF THE  
ELONGATED TROF BY SUNDAY...PROVIDING A BIT MORE OVERALL CONFIDENCE  
EVEN THOUGH SMALL VARIATIONS (MAGNITUDE OF INTERNAL SHORTWAVES)  
CONTINUE TO VARY RUN TO RUN. ALL IN ALL A GENERAL MODEL BLEND  
SEEMS PRUDENT...AND CONFIDENCE IS RISING TO SLIGHTLY ABOVE AVERAGE  
FOR THIS BLEND.  
 
...NEXT SHORTWAVE AMPLIFYING ACROSS THE SOUTHERN CANADIAN PRAIRIES  
EARLY SUNDAY WITH ASSOCIATED FRONTAL ZONE ACROSS THE DAKOTAS...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 00Z GFS/UKMET/CMC BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
BY LATE SATURDAY A SHORTWAVE OVER TOPS THE STRONG WESTERN NORTH  
AMERICAN CONTINENT RIDGE DESCENDING INTO THE CENTRAL PRAIRIE  
PROVIDENCES...AND GIVEN THE SPACING BETWEEN THE RIDGE AND  
DOWNSTREAM MERIDIONAL TROF...BEGINS TO AMPLIFY PRESSING HEIGHT  
FALLS SOUTHEAST HELPING TO SPUR SURFACE DEVELOPMENT AS WELL AS  
STRONG DOWN SLOPING OFF THE NORTHERN US ROCKIES INTO THE PLAINS BY  
EARLY SUNDAY. THE 12Z CMC IS MOST OUT OF PHASE FAVORING A  
STRONGER MORE CONSOLIDATED CENTRAL CORE THAT REMAINS FURTHER NORTH  
THAN OTHER GUIDANCE. OTHERWISE THE THE DIFFERENCES ARE FAIRLY  
SMALL FOR DAY 3 AND CONSISTENT WITH THE MEAN ENSEMBLE SUITE TO  
SUPPORT A NON-CMC BLEND AT SLIGHTLY ABOVE AVERAGE CONFIDENCE.  
 
07Z UPDATE: THE 00Z ECMWF TRENDED FASTER THAN THE 12Z RUN AND IS  
UNCHARACTERISTICALLY FASTEST OF THE OVERALL SOLUTIONS...PERHAPS A  
BIT TOO FAST. THE 00Z CMC HAS BACKED OFF THE NORTHERN SOLUTION  
AND IS MATCHING THE OVERALL TIMING OF THE 00Z GFS. THIS IS  
MATCHED BY THE 00Z UKMET MAKING A STRONGER CENTRAL/MODESTLY  
AMPLIFIED SOLUTION EVEN WITH THE BROADER BUT SLOWER NAM. THE 00Z  
GEFS MEAN AND 12Z ECENS MEAN CONTINUE TO FAVOR THIS MIDDLE GROUND  
SOLUTION...PROVIDING SOME ADDITIONAL CONFIDENCE IN THE BLEND. AS  
SUCH WILL SUGGEST A 00Z GFS/UKMET/CMC BLEND AT SLIGHTLY ABOVE  
AVERAGE CONFIDENCE.  
 
...TROPICAL WAVE/DISTURBANCE CURRENTLY IN THE WESTERN CARIBBEAN  
AND APPROACHING THE FLORIDA STRAITS BY THIS WEEKEND...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-UKMET BLEND  
CONFIDENCE: AVERAGE  
 
A BROAD AREA OF LOW PRESSURE WAS SITUATED OVER THE WESTERN  
CARIBBEAN SEA AND CENTRAL AMERICA...AND MODELS SHOW THIS SLOWLY  
CONSOLIDATING OVER THE NEXT COUPLE DAYS. THE 00Z GFS REMAINS ON  
THE WESTERN EDGE OF THE MODEL SPREAD ALONG WITH THE 12Z ECMWF  
HOWEVER THE GFS BEING A BIT FASTER WITH THE NORTHERN STREAM BASE  
OF THE TROF LEADING TO A BIT MORE INCREASED VERTICAL SHEAR ON THE  
SYSTEM THAN THE SLIGHTLY SLOWER ECMWF. THE 00Z NAM SEEMS A GOOD  
BLEND BETWEEN THE TWO HAVING THE STRENGTH OF THE ECMWF BUT THE  
TIMING/NORTHERN STREAM INTERACTION OF THE GFS BUT IN DOING SO  
PRESENT A MUCH DIFFERENT SURFACE EVOLUTION. THE 12Z UKMET IS A  
CLEAR OUTLIER HAVING A MUCH STRONGER WAVE REFLECTION LIFTING OUT  
OF THE WESTERN CARIBBEAN. ALL CONSIDERED WILL CONTINUE A 00Z GFS  
AND 12Z ECMWF BLEND AS PREFERENCE BUT CONFIDENCE IS AVERAGE GIVEN  
THE MODEST SPREAD DUE TO MULTI-STREAM CONFLUENCE/INFLUENCES.  
 
07Z UPDATE: THE 00Z ECMWF PICKED UP A BIT OF PACE AND WHILE STILL  
SLOWER THAN THE NAM IS MATCHED BY THE 00Z CMC...MAKING THE GFS A  
BIT TOO FAST AND MORE SHEARED/WEAKER THAN THE OTHER GUIDANCE WOULD  
SUGGEST. THE UKMET CONTINUES TO BE MUCH STRONGER AND EAST OF THE  
OTHER GUIDANCE. ALL CONSIDERED A NON-UKMET BLEND SEEMS BEST  
REPRESENTS THE MODEST ENSEMBLE SPREAD. CONFIDENCE REMAINS AVERAGE.  
 
BREAKDOWN OF WESTERN UPPER RIDGE AND SHORTWAVE SHIFTING INTO  
SOUTHERN CA BY SUN  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-UKMET BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
A COMPACT FAIRLY SYMMETRIC SHORTWAVE EXISTS OUT NEAR 30N130W AT  
THE BASE OF A REX PATTERN WITH STRONG 588DM RIDGE JUST OFF THE  
PACIFIC NORTHWEST. THIS RIDGE WILL SLOWLY SHIFT EAST AND SOUTH  
AND SLOWLY INTO THE WEST COAST BY SAT...WITH GUIDANCE QUITE  
STRONGLY AGREEING. AS THE RIDGE BREAKS DOWN THE SHORTWAVE SHIFTS  
EASTWARD...AND IN DOING SO THE CMC BECOMES A BIT FASTER AND SOUTH  
OF THE GREATEST CLUSTERING. THIS CONTINUES AS IT REACHES THE  
SOUTHWEST CA COAST BY THE END OF THE FORECAST PERIOD. AS SUCH A  
NON-CMC BLEND IS SUGGESTED AT SLIGHTLY ABOVE AVERAGE CONFIDENCE.  
 
07Z: THE 00Z CMC SHIFTED NORTH AND A BIT BROADER WITH THE  
SYMMETRIC SHORTWAVE ENTERING SW CA BY SUNDAY MORNING MATCHING THE  
00Z ECMWF/NAM AND GFS. THE 00Z UKMET HOWEVER IS NOW THE CLEAR  
OUTLIER...MUCH DEEPER AND MUCH FURTHER SOUTH HAVING MAINTAINED THE  
CORE OF THE RIDGE OFF THE SW OR COAST RATHER THAN BUILDING IT  
SOUTHWARD INTO S CA ON SAT LIKE THE OTHER GUIDANCE. AS SUCH A  
NON-UKMET BLEND IS SUPPORTED AT SLIGHTLY ABOVE AVERAGE CONFIDENCE.  
 
WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML  
WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML  
 
GALLINA  
 

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab HPC Page Main Text Page