219  
FXUS10 KWNH 131846  
PMDHMD  
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
245 PM EDT FRI OCT 13 2017  
 
VALID OCT 13/1200 UTC THRU OCT 17/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z MODEL PREFERENCES INCLUDING FORECAST CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
FRONT MOVING INTO THE GREAT LAKES/NORTHEAST FRIDAY/SATURDAY  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
CONTINUED VERY STRONG MODEL AGREEMENT WITH LITTLE CHANGE ON THE  
12Z NAM/GFS CONTINUES ABOVE AVERAGE CONFIDENCE IN A GENERAL MODEL  
BLEND ACROSS THE GREAT LAKES/NORTHEAST/MID-ATLANTIC OVER THE NEXT  
FEW DAYS.  
 
SYSTEM MOVING FROM THE NORTHWEST INTO THE GREAT LAKES  
SUNDAY...ATTENDANT FRONTAL ZONE CROSSING EASTERN THIRD OF US LATE  
SUN TO TUES  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-NAM BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
AS THE SHORTWAVE LIFTS OUT OF THE ROCKIES THE LOCATION OF THE  
SHORTWAVE CORE (NORTH TO SOUTH) LEADS TO THE MORE SIGNIFICANT  
DIFFERENCES IN MASS FIELDS. THE 12Z NAM WHILE MUCH QUICKER THAN  
THE PRIOR 00Z/06Z RUNS...REMAINS WELL SOUTH WITH THE CORE AND AS  
SUCH THE SURFACE REFLECTION IS ALSO FURTHER SOUTH THAN PRIOR WPC  
PREFERENCES ANCHORED BY THE 00Z ECMWF/UKMET AND GFS ITERATIONS.  
THE 00Z CMC LIKE THE NAM IS FURTHER SOUTH THOUGH REMAINS SLOW  
OVERALL. THE 12Z GFS HAS SHIFTED SLIGHTLY FURTHER SOUTH THAN THE  
00Z/06Z RUNS THIS LEAVES IT ABOUT A THIRD OF THE WAY BETWEEN THE  
ECMWF AND CMC. THIS SLOWER SOLUTION ALSO ALLOWS FOR INCREASED  
SW-NE ELONGATION OF THE WAVE REDUCING THE DRY SLOT SPACING ACROSS  
IA/WI/MI THAN PRIOR RUNS...BUT ALL IN ALL THE DIFFERENCES ARE  
FAIRLY SMALL TO KEEP THE 12Z GFS AND 00Z ECMWF/UKMET BLEND AS  
PREFERENCE BUT SLIGHTLY REDUCED CONFIDENCE OVERALL GIVEN THE  
SHIFTS IN THE 12Z NAM/GFS SOLUTIONS; YET THIS IS STILL SLIGHTLY  
ABOVE AVERAGE.  
 
19Z UPDATE: THE 12Z ECMWF AND UKMET SEEMS TO HAVE SWAP PLACES WITH  
THE ECMWF SHIFTING FASTER AND THE UKMET SHIFTING SLOWER. THE 12Z  
CMC SHIFTED A BIT NORTH BUT ALSO FASTER...REDUCING THE OVERALL  
SPREAD BUT STILL NOT COMING TO A COMMON SOLUTION JUST YET. THE  
CLUSTERING IS TIGHTEST WITH THE ECMWF/UKMET/CMC AS WELL AS THE GFS  
IS A BIT OUT OF PHASE AND SUGGEST LOWERING ITS WEIGHTING IN THE  
BLEND. AS SUCH A NON-NAM BLEND IS SUGGESTED AT SLIGHTLY ABOVE  
AVERAGE CONFIDENCE.  
 
KICKER SHORTWAVE DROPPING INTO THE GREAT LAKES SUNDAY NIGHT  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
AS EXPECTED THE EVOLUTION OF THE NEXT KICKER WAVE STREAKING ACROSS  
SOUTHERN CANADA INTO THE UPPER MIDWEST SUNDAY ARE AFFECTED BY  
DOWNSTREAM EVOLUTION. INTERESTINGLY...THE 12Z NAM/GFS BOTH  
SUGGESTED A GREATER UNFOLDING OF THE SHORTWAVE AMPLIFYING FURTHER  
SOUTH ACROSS THE OHIO RIVER VALLEY BY MONDAY...SEEMINGLY MATCHING  
MORE OF A UKMET/CMC SOLUTION THAT ARE GENERALLY SHARPER THAN THE  
MORE CONSOLIDATED/ROUNDER BASE OF THE TROF PRESENTED BY THE ECMWF.  
THIS IS A VERY MINOR DIFFERENCE PARTICULARLY IN SENSIBLE WX  
FIELDS BUT GIVEN THE SHIFTS TOWARD THIS INCREASED AMPLIFICATION  
WILL SUGGEST A NON-ECMWF BLEND AT SLIGHTLY ABOVE AVERAGE  
CONFIDENCE FOR THE EVOLUTION OF THIS WAVE AND ITS EFFECTS THE THE  
TRAILING FRONTAL ZONE/MOISTURE RETURN TOWARD IT ACROSS THE  
SOUTHERN STATES.  
 
19Z UPDATE: THE 12Z ECMWF AMPLIFIED IN LINE WITH OTHER GUIDANCE TO  
ONCE AGAIN SUPPORT A GENERAL MODEL BLEND AT ABOVE AVERAGE  
CONFIDENCE FOR THIS KICKER WAVE.  
 
TROPICAL WAVE MOVING THROUGH THE FL STRAITS  
LINGERING UPPER TROUGH/UPPER LOW NEAR THE BAHAMAS INTO MONDAY  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-UKMET BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
THE 12Z NAM CONTINUES TO BE ON THE DEEPER/STRONGER SIDE (AS IT  
TYPICALLY IS...LIKELY RELATED TO GRID SCALE RESOLUTION) BUT STILL  
MATCHES WELL WITH SHAPE/EVOLUTION AND PLACEMENT WITH RESPECT TO  
THE 12Z GFS, 00Z ECMWF/UKMET AND ENSEMBLE SUITE. THE 00Z UKMET  
REMAINS UNIQUELY WEAKER WITH THE SYSTEM PARTICULARLY AFTER THE  
TROPICAL WAVE MOVES THROUGH WITH THE REMAINING ENERGY OVER THE  
BAHAMAS. AS SUCH A NON-UKMET BLEND REMAINS PREFERRED. CONFIDENCE  
IS ABOVE AVERAGE AS EVEN THIS WEAK RESOLUTION REMAINS FAIRLY TIGHT  
IN PLACEMENT.  
 
19Z UPDATE: THE 12Z UKMET REMAINED UNIQUELY WEAKER THAN THE OTHER  
GUIDANCE (12Z ECMWF/CMC/GEFS SHOWS LITTLE CHANGE AS WELL) TO KEEP  
A NON-UKMET PREFERENCE AT ABOVE AVERAGE CONFIDENCE.  
 
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GALLINA  
 

 
 
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