106  
FXUS10 KWNH 290444  
PMDHMD  
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1243 AM EDT SUN OCT 29 2017  
 
VALID OCT 29/0000 UTC THRU NOV 01/1200 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
00Z MODEL EVALUATION...WITH FINAL PREFERENCES AND CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
   
..TROPICAL STORM PHILIPPE
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
NHC BEST PROXY: 00Z NAM/18Z GEFS BLEND  
PLEASE REFER TO NHC FORECASTS  
 
DUE TO UNCERTAINTY OF INITIAL CENTER LOCATION/CONSOLIDATION  
CURRENTLY OCCURRING ACROSS THE FL STRAITS...NHC FORECAST IS BASED  
MAINLY ON 21Z FCST BLENDED WITH NEARLY ALL GUIDANCE MEMBERS AND  
SHIFTED NORTH. THIS DOES NOT LEAVE MANY OPTIONS FOR A PROXY TO  
MATCH NHC. HOWEVER...THE 00Z NAM WHILE SOUTHEAST OF THE OFFICIAL  
TRACK DOES EVENTUALLY BECOME MORE ALIGNED IN TIMING AS THE SYSTEM  
GOES POST-TROPICAL BY 36HRS...THE 18Z GEFS WHILE NOT AS FAST  
NORTHWEST AS THE 18Z OR 00Z GFS... SEEMS A GOOD PROXY TO START  
WITH PARTICULARLY FOR THE FIRST 24HRS. AS SUCH A BEST PROXY IS A  
BLEND OF THE 18Z GEFS MEAN AND THE 00Z NAM... WEIGHTING HEAVY GEFS  
FOR 0-24HRS SWITCHING HEAVY 00Z NAM 24-48HRS.  
 
...KICKER SHORTWAVE CURRENTLY IN CENTRAL MS VALLEY DIGS INTO BASE  
OF THE LONGWAVE TROUGH OVER THE SOUTHEAST TODAY...  
...INCREASINGLY NEGATIVE TILT TROUGH EJECTING UP THE EAST COAST  
SUNDAY AND MONDAY WITH RAPID CYCLOGENESIS...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 00Z NAM AND 12Z ECMWF/UKMET BLEND  
(HEAVILY INCL. 12Z ECENS MEAN IF AVAILABLE)  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
WHILE GUIDANCE CONTINUES TO LOCK DOWN ON TIMING...THE  
SHAPE/EVOLUTION OF THE SHORTWAVE LIFTING ALONG THE EAST COAST (AND  
SUBTROPICAL INFLUENCES FROM PHILIPPE) LEAD TO SMALL YET CRITICALLY  
IMPORTANT DIFFERENCES IN THE STRENGTH/TRACK OF THE MASS FIELDS.  
AS BEEN THE CASE THROUGH MUCH OF THE EVOLUTION THE ECENS MEAN  
CONTINUES TO ANCHOR THE GUIDANCE TO PROVIDE CONFIDENCE AND  
CONTINUITY...THE GFS/GEFS HAS BEEN MORE VARIANT WITH TIME AND ONCE  
AGAIN THE 00Z (AND 18Z) RUNS DEPICT A FAST BIAS AND FLATTER  
SOLUTION LEADING THE MASS FIELDS TO BE JUST OFF ESPECIALLY GIVEN  
THE ABSORPTION OF TS PHILIPPE ACROSS SOUTHEAST NEW ENGLAND ON  
MONDAY. THE 00Z NAM SHOWS A BIT OF THIS INTERACTION AND BETTER  
MATCHES THE OFFICIAL NHC 03Z FORECAST...BUT ALSO THE EVOLUTION OF  
THE SHORTWAVE TROF LOOKS MORE INLINE WITH THE ECENS MEAN. THE 12Z  
ECMWF IS ALSO QUITE REPRESENTATIVE OF THE OVERALL ECENS SUITE...TO  
HELP ANCHOR THE BLEND. THE 12Z UKMET WHILE A BIT SLOWER AND MORE  
WOUND UP THAN THE NAM/ECMWF SHOWS ENOUGH SIMILARITY TO SUGGEST ITS  
INCLUSION AS WELL. AS SUCH A BLEND OF THE 00Z NAM AND 12Z  
ECMWF/UKMET IS PREFERRED BUT IF ONE HAS THE ECENS MEAN TO  
BLEND...WEIGHTING HEAVIER TO THAT SOLUTION WOULD GIVE THE GREATEST  
CONFIDENCE.  
 
...SHORTWAVE DIGGING INTO THE NORTHERN PLAINS BY SUNDAY AND  
PHASING WITH EAST COAST CYCLONE INTO MONDAY AND TUESDAY...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-UKMET BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
SHORTWAVE CURRENTLY DROPPING OUT OF N MANITOBA WILL CONTINUE TO  
AMPLIFY INTO THE WESTERN GREAT LAKES WITH FAIRLY GOOD CONSISTENCY  
IN EVOLUTION AND SHAPE. THE TWO AREAS OF DEPARTURE IN GUIDANCE  
ARE HOW SHARP THE JET STREAK UNDERCUTS THE EAST COAST WAVE AND THE  
LINGERING TRAILING WESTERN PORTION OF THE WAVE CROSSING THE  
NORTHERN PLAINS/MIDWEST MON/TUES. WITH RESPECT TO THE PRIOR...THE  
12Z UKMET IS MOST AGGRESSIVELY SURGING THE JET STREAK UNDER THE  
NORTHWARD LIFTING WAVE ACROSS THE WESTERN GREAT LAKES WHILE THE  
ECMWF IS LEAST ENGAGING...THIS MAY BE LEADING TO THE SMALL WEST  
WOBBLE IN TRACK OF THE EAST COAST WAVE BUT IT APPEARS TO BE MINOR  
THAT A GENERAL MODEL BLEND COULD WORK OUT. THE LATTER ISSUE IS A  
BIT MORE UNCERTAIN WITHIN THE GUIDANCE/ENSEMBLE SUITE. THE 12Z  
UKMET APPEARS TO BE A FAST OUTLIER HERE AS WELL WITH A FLATTER  
SOLUTION STREAKING ACROSS THE LOWER GREAT LAKES BY 12Z TUES WHILE  
THE 00Z GFS/NAM AND 12Z ECMWF ARE A BIT MORE AMPLIFIED ACROSS IL  
AND REMAINING AS SHARP THROUGH NEW ENGLAND 00Z WED. THE 12Z CMC  
IS ALSO FLAT BUT NOT AS FAST AS THE UKMET. ALL CONSIDERED WILL  
RETAIN THE CMC TO HEDGE FOR THE FLATTER SOLUTION BUT GIVEN SMALL  
DIFFERENCES IN THE TWO AREAS...A NON-UKMET BLEND IS SUGGESTED.  
CONFIDENCE IS ABOVE AVERAGE AS THE OVERALL SPREAD AND AFFECTS TO  
SENSIBLE WX ARE SMALLER THAN AVERAGE.  
 
...PAIR OF SHORTWAVES SLIDING DOWN EASTERN FLANKS OF CANADIAN  
ROCKIES INTO THE NORTHERN PLAINS...EXPANDING THE GLOBAL TROF  
FURTHER WEST TUES INTO WED WITH ACCOMPANYING BROAD/DEEP SURFACE  
WAVE ALONG NORTHERN TIER WED...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 00Z NAM/GFS AND 12Z ECMWF BLEND  
CONFIDENCE: SLIGHTLY BELOW AVERAGE  
 
STRONG WARM RIDGE OVER THE NORTHEAST PACIFIC AND VERY FIRST  
VESTIGES OF DEEP ARCTIC COLD BLEEDING IN OFF THE ARCTIC OCEAN  
SUPPORT A VERY STRONG JET ACROSS NORTHWEST CANADA MON/TUESDAY.  
EVENTUALLY THE JET DEAMPLIFIES THE NORTHEAST EXTENSION OF THE  
PACIFIC RIDGE IN BC BY LATE TUESDAY. THE FIRST IN A PAIR OF SOLID  
SHORTWAVES AMPLIFIES IN THE EXIT REGION OF THE JET SUPPORTING  
WESTWARD EXPANSION OF THE GLOBAL TROF INTO THE NORTHERN PLAINS  
TOWARD THE WESTERN ROCKIES. THIS WAVE SWINGS THROUGH THE NORTHERN  
PLAINS INTO THE GREAT LAKES WITH LITTLE FANFARE. TIMING SEEMS TO  
BE THE GREATEST DIFFERENCE HERE...AS THE 00Z GFS IS  
UNCHARACTERISTICALLY SLOW AND THE 12Z CMC A BIT FASTER BUT ALSO A  
BIT FURTHER SOUTH COMPARED TO THE 00Z NAM/ECMWF WHICH ARE BEST  
MATCHED WITHIN THE ENSEMBLE SUITE.  
 
THE GREATER SPREAD AND SIGNIFICANT WEATHER PRODUCER IS RELATED TO  
THE CORE OF THE JET AND WHILE THE FLOW IS HIGHLY POSITIVELY TILTED  
SO MUCH SO THAT IT IS ESSENTIALLY FLAT NW TO SE FROM BC INTO THE  
DAKOTAS. HOWEVER THE ENERGY/COLD AIR IT BRINGS SUPPORTS A  
DEEP/BROAD SURFACE WAVE BY WED ACROSS THE NORTHERN TIER. THE  
ISSUES WITH THE SOUTHWARD LEADING WAVE IN THE CMC APPEAR TO COME  
TO ROOST AS THIS WAVE IS FASTER THAN OTHER GUIDANCE WITH A WELL  
FORWARD SURFACE WAVE WITHIN THE GUIDANCE CLUSTER. OTHERWISE THE  
REMAINING GUIDANCE IS QUITE WELL PLACED WITH THE NORTHERN PORTION  
OF THE WAVE AND SURFACE REFLECTION. HOWEVER THE TRAILING TROF IS  
MUCH MORE FORWARD/STRONGER INTO THE PACIFIC NORTHWEST BY THE 12Z  
UKMET. THE 00Z NAM/GFS ARE SLOWER THAN THE 12Z ECMWF WITH THE  
TRAILING TAIL END OF THE TROF STILL BACK OVER THE WESTERN GULF OF  
AK...BUT THIS APPEARS MORE SENSIBLE IN THE ENSEMBLE SUITE AND RUN  
TO RUN SPAGHETTI ANALYSIS. STILL GIVEN THIS IS A CLEAR PATTERN  
CHANGING SYSTEM AND ITS VAST SIZE A BLEND OF THE 00Z GFS/NAM AND  
12Z ECMWF APPEAR A GOOD PROXY FOR THE ENSEMBLE SUITE AND TRENDS  
OVERALL...HOWEVER CONFIDENCE IS SLIGHTLY BELOW AVERAGE GIVEN THE  
POTENTIAL FOR ADDITIONAL CHANGES.  
 
...MID-UPPER LEVEL LOW MOVING INTO THE SOUTHWEST MONDAY AND  
TUESDAY SHEARING INTO FLOW ACROSS SOUTHERN PLAINS WED...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
REMARKABLE SYMMETRY EXISTS WITHIN THE GUIDANCE SUITE WITH THE  
LOCATION/STRENGTH OF THE WAVE INCLUDING THE EVENTUAL SHEARING INTO  
THE CONFLUENT FLOW ACROSS THE SOUTHERN PLAINS BY WED. AS SUCH A  
GENERAL MODEL BLEND CAN BE PREFERRED AT ABOVE AVERAGE CONFIDENCE.  
   
..WEAK SHORTWAVE ENTERING PACIFIC NORTHWEST LATER TODAY
 
DIGGING  
TOWARD CENTRAL COASTAL CALIFORNIA BY TUES AND SETTLING OFF SW CA  
COAST BY WED...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
OVERALL THE TIMING OF THE WEAK SHORTWAVE IS QUITE STRONG ENTERING  
THE PACIFIC NORTHWEST BY LATE SUNDAY AS WELL AS DROPPING SOUTH  
INTO COASTAL CALIFORNIA BY TUESDAY MORNING....IT IS AT THIS TIME  
SMALL DIFFERENCES IN THE EXTENT OF ELONGATION BACK UNDER THE  
NORTHEAST PACIFIC OCEAN ANTICYCLONE APPEARS THE GREATEST  
DIFFERENCE. THE 12Z ECMWF IS MORE COMPACT AND DOES NOT SHEAR AS  
FAR WESTWARD... THOUGH WEAKENS THE CENTRAL CORE OF THE WAVE. THE  
12Z CMC IS ALSO COMPACT AND WHILE THERE IS STRETCHING ON PAR WITH  
THE GFS/NAM AND UKMET... THE INNER CORE REMAINS MORE ROUNDED.  
IMPACTS TO SENSIBLE WEATHER DO NOT SEEM DRAMATIC AND A GENERAL  
MODEL BLEND SHOULD SUFFICE TO ROUND OUT THESE DIFFERENCES.  
CONFIDENCE IS SLIGHTLY ABOVE AVERAGE.  
 
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