661  
FXUS10 KWNH 111655  
PMDHMD  
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1254 PM EDT WED OCT 11 2017  
 
VALID OCT 11/1200 UTC THRU OCT 15/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
00Z PRELIMINARY MODEL EVALUATION...INCLUDING PREFERENCES/CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
...TROUGH DEAMPLIFYING AND ACCELERATING TO THE NORTHEAST U.S.  
COAST BY THURSDAY AND ACCOMPANYING WEAK SURFACE LOW IN THE UPPER  
MIDWEST / OHIO VALLEY...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-CMC BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
IN GENERAL...THERE REMAINS EXCELLENT MODEL AGREEMENT WITH THIS  
SYSTEM. THE LONE AND ALSO FAIRLY SMALL EXCEPTION REMAINS WITH THE  
CMC. THE 00Z CMC SHOWS HIGHER HEIGHTS THROUGH THE DEPTH OF THE  
RIDGE OVER MUCH OF THE EASTERN CONUS. THIS LEADS TO A FASTER  
EJECTION AND DEAMPLIFICATION OF THE WAVE THAN ALMOST ALL OTHER  
MODELS...AND THE RIDGE BUILDING IN ACROSS THE EASTERN U.S. FASTER.  
AS SUCH A NON-CMC BLEND IS CONSIDERED PREFERENCE AT ABOVE  
AVERAGE CONFIDENCE.  
 
...UPPER TROUGH ARRIVING IN THE NORTHWESTERN U.S. WITH LEAD  
SHORTWAVE EJECTING TO HUDSON BAY BY THE WEEKEND...  
...ATTENDANT SURFACE CYCLONE DEVELOPING INTO CANADA AND ASSOCIATED  
COLD FRONT CROSSING THE NW REACHING NRN PLAINS ON THURSDAY AND  
GREAT LAKES TO CENTRAL PLAINS FRI/SAT...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
THERE REMAIN SOME SMALL DIFFERENCES MAINLY WITH THE INNER CORE OF  
THE SHORTWAVE/REFLECTED SURFACE LOW WELL NORTH INTO CENTRAL  
CANADA. THE 12Z NAM CONTINUES THE TREND TOWARD THE STRONGER  
CONSENSUS PRESENTED BY THE ECMWF/GEFS/ECENS MEAN/CMC AND UKMET.  
THE 12Z GFS SHIFTED A BIT FURTHER NORTH . ENOUGH TO SUPPORT A  
GENERAL MODEL BLEND AT ABOVE AVERAGE CONFIDENCE.  
 
...SECONDARY SHORTWAVE DIGGING SOUTH INTO THE WESTERN U.S. FROM  
LATE THURSDAY INTO FRIDAY SPURRING A WEAK SURFACE WAVE ALONG  
FRONTAL BOUNDARY IN PLAINS LATE SAT INTO SUN...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND UP TO 14/00Z  
2/3 00Z ECMWF & 1/3 12Z NAM AFTERWARD  
CONFIDENCE: ABOVE AVERAGE UP TO 14/00Z  
SLIGHTLY BELOW AVERAGE THEREAFTER  
 
SHORTWAVE ENERGY CURRENTLY IN CENTRAL AK WILL DESCEND ON THE  
WESTERN SIDE OF THE TROF/DIG AND REPLACE THE EXITING SHORTWAVE TO  
RESET THE WESTERN TROF OVER THE NORTHWEST US BY LATE FRIDAY/EARLY  
SAT. THE SHORTWAVE WILL COME IN TWO SURGES AND MODEL SPREAD HAS  
INCREASED BASED ON THE SLIGHT TIMING DIFFERENCES OF THESE FEATURES  
MAINLY AS THE TROF ADVANCES EAST AND TILTS MORE POSITIVELY TOWARD  
LATE SATURDAY. THE 12Z NAM/GFS BOTH SHOWED A SLIGHTLY FASTER AND  
STRONGER REPRESENTATION OF THE LEAD SHORTWAVE ROUNDING THE TROF  
BASE ACROSS THE NORTHERN ROCKIES SUPPORTING EARLIER/STRONGER  
HEIGHT FALLS INTO THE NORTHERN PLAINS; WITH THE GFS A BIT STRONGER  
THAN THE NAM. AS SUCH THE 12Z GFS ALSO SUPPORTS A STRONGER  
SURFACE REFLECTION ALONG THE THE DRAPED FRONTAL ZONE IN THE  
CENTRAL PLAINS...SHIFTING FASTER INTO NE IA BY 00Z SUN. THE NAM  
IS MORE RESERVED AND SLOWER CLOSER TO KC METRO. THE 00Z ECMWF/CMC  
LOAD THE TROF WITH A STRONGER SECONDARY WAVE AND WITH A WEAKER  
LEAD WAVE...ALLOWS FOR FURTHER SOUTHWARD DIGGING AND OVERALL  
NARROWING OF THE TROF FROM NNE-SSW BY 00Z SUN...WITH THE CMC EVEN  
LAGGING FURTHER BACK TO THE ECMWF. THE 00Z UKMET SEEMS A SPLIT IN  
THE DIFFERENCE IN TIMING... THOUGH FAVORING THE STRENGTH OF THE  
SECOND WAVE (LIKE THE ECMWF) IS A BIT FASTER LIKE THE NAM OR EVEN  
GFS...THOUGH IN THE COMPROMISE...STRONG NORTHERN FLOW LEADS TO A  
MORE SUBSTANTIAL POSITIVE TILT TO THE TROF OVERALL (LEADING TO  
DEPARTURE IN QPF ORIENTATION/AXIS IN THE LEE OF THE NORTHERN  
ROCKIES/NORTHERN PLAINS. THE OVERALL ENSEMBLE SUITE (ANCHORED BY  
THE 00Z ECENS MEAN/06Z GEFS MEAN) WOULD FAVOR SOMETHING CLOSER TO  
THE 00Z ECMWF.  
 
HOWEVER...THIS RUN MAY BE THE FIRST TO BETTER SAMPLE THE  
ORIGINATING SHORTWAVE NOW THAT IT BECOMING RESOLVED IN THE RAOB  
NETWORK AND THE 12Z NAM/GFS MAY BE FIRST TO SUGGEST THIS TREND.  
OVERALL THIS ADDS UNCERTAINTY MAINLY AFTER 00Z SAT. AS SUCH WILL  
HEDGE BY SUGGESTING A 2/3RDS 00Z ECMWF BLEND WITH 1/3 12Z NAM  
AFTER 00Z SAT BUT WILL REASSESS CHANGES BASED ON THE 12Z SHIFTS IN  
THE NON-NCEP SUITE AND 12Z GEFS. CONFIDENCE IS SLIGHTLY BELOW  
AVERAGE ON SAT BUT ABOVE AVERAGE UNTIL 14/00Z (GENERAL MODEL BLEND)  
 
...TROPICAL WAVE CURRENTLY NEAR HISPANIOLA MOVING WEST TO NEAR  
FLORIDA BY FRIDAY...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-CMC BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
OVERALL MASS FIELDS CONTINUE TO SHOW FAIRLY STRONG MODEL AGREEMENT  
WITH THE PLACEMENT/TIMING OF THE TROPICAL WAVE CROSSING S FL/CUBA  
AND BAHAMAS POSITIVELY TILTING ACROSS THE SARGASSO SEA. THE  
FLATTENING OF THE WAVE ALLOWS FOR INCREASED EASTERLY FLOW ACROSS  
FL INTO SAT. THE MODELS DEPICT SIMILAR EVOLUTION IN THE MASS  
FIELDS WITH EXCEPTION TO THE 00Z CMC. THE CMC IS A BIT SLOWER AND  
MORE AMPLIFIED OVER THE NORTHEAST EXTENSION OF THE INVERTED TROF  
EVEN SUPPORTING A WEAK CLOSED OFF SURFACE REFLECTION NORTHEAST AND  
NORTH OF THE N BAHAMAS THURS/FRI. GIVEN REMAINING SIMILARITY A  
NON-CMC SOLUTION IS PREFERENCE AT ABOVE AVERAGE CONFIDENCE.  
 
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GALLINA  
 

 
 
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