056  
FXUS10 KWNH 280642  
PMDHMD  
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
242 AM EDT SAT OCT 28 2017  
 
VALID OCT 28/0000 UTC THRU OCT 31/1200 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
00Z MODEL EVALUATION...WITH FINAL PREFERENCES AND CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
...OCCLUDED CYCLONE OVER THE WESTERN GREAT LAKES GRADUALLY  
WEAKENING AND LIFTING NNE TO NEAR HUDSON BAY...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
MODELS ARE IN EXCELLENT AGREEMENT WITH THIS SYSTEM...SHOWING VERY  
LITTLE DIFFERENCE AMONG A VARIETY OF MASS FIELDS. THEREFORE...A  
GENERAL MODEL BLEND IS PREFERRED WITH HIGH CONFIDENCE.  
 
   
..POTENTIAL TROPICAL CYCLONE EIGHTEEN
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
NHC BEST PROXY: 00Z GFS/ECMWF AND 21Z SREF MEAN  
PLEASE REFER TO NHC FORECASTS  
 
NHC HAS OFFICIALLY BEGUN FORECASTS ON THE SYSTEM EXITING THE  
WESTERN GULF TOWARD THE FL STRAITS...AND CURRENT FORECAST TRACK IS  
QUITE SIMILAR TO THE 00Z GFS/12Z UKMET UNTIL ABOUT 30HRS (29/06Z)  
WHEN THE UKMET BECOMES A BIT TOO DEEP AND SLOW RESPECTFULLY. THE  
00Z NAM IS ALSO QUITE SIMILAR IN THE TRACK TO THE OFFICIAL  
FORECAST THOUGH IS A BIT SLOWER BUT ALSO A BIT WEAKER OVERALL  
GENERALLY WASHING OUT THE SYSTEM (THROUGH SHEARING EFFECTS) BY  
LATE SUNDAY THROUGH THE NORTHERN BAHAMAS. THE 12Z CMC A BIT SLOW  
AND LEFT OF THE TRACK BUT ALSO TYPICAL OF THE CMC DEEPENS UNDER  
THE BAROCLINIC/SHEARING FORCES AND LIFTS IT NORTHWARD ALONG THE  
GULF STREAM TOWARD CAPE COD BY MONDAY...CLEARLY NOT IN LINE WITH  
THE NHC FORECAST. THE 12Z ECMWF LIKE THE NAM IS A WEAK  
REPRESENTATIVE IN TH SUITE AND DEVIATES WEST/LEFT OF TRACK TOWARD  
SW FL. AS SUCH THE 00Z GFS OR PERHAPS THE 21Z SREF MEAN MAY BE  
THE BEST REPRESENTATION TO THE NHC FORECAST TRACK.  
 
07Z UPDATE: THE 00Z UKMET SHOWS SIMILAR TIMING/STRENGTH ISSUES AS  
THE 12Z RUN BUT HAS SHOWS A STRONGER AGREEMENT IN THE TRACK  
FORECAST EVEN THROUGH 48HRS BUT IS ON PAR/SLIGHTLY SLOW BEFORE IT  
CONTINUES TO DEEPEN LIFTING NORTHWARD TOWARD GEORGES BANK. THE CMC  
MATCHES TIMING WITH THE GFS/SREF PERHAPS A BIT LEFT THROUGH 36HRS  
BUT LIKE THE 12Z RUN RAPIDLY DEEPENS THE CYCLONE AND RACES IT NNE  
TOWARD CAPE COD. THE ECMWF WHILE STILL A BIT LEFT OF THE OFFICIAL  
TRACK IS FAIRLY WELL TIMED WITH THE GFS/SREF AND COULD BE INCLUDED  
TO A BLEND THOUGH THE GFS IS LIKELY THE BEST SINGLE PROXY WITHIN  
THIS CLUSTER.  
 
...KICKER SHORTWAVE DIGGING FROM GREAT LAKES INTO BASE OF THE  
LONGWAVE TROUGH OVER THE SOUTHEAST THIS WEEKEND...  
...INCREASINGLY NEGATIVE TILT TROUGH EJECTING UP THE EAST COAST  
SUNDAY AND THROUGH NEW ENGLAND BY TUES...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 00Z GFS/ECMWF  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
MASS FIELDS ARE BEGINNING TO SOLIDIFY IN A COMMON SOLUTION EVEN  
GIVEN THAT SUBTLE TIMING/ORIENTATIONS OF SMALL SCALE FEATURES MAY  
LEAD TO FEEDBACK MECHANISMS LEADING TO FAIRLY DIFFERENT OUTCOMES.  
DETERMINISTIC/ENSEMBLE GUIDANCE HAVE COME TO STRONG AGREEMENT IN  
PLACEMENT/ORIENTATION OF THE SHORTWAVE AS IT BECOMES NEGATIVE TILT  
AND CLOSES OFF OVER THE CAROLINAS. DIFFERENCES BEGIN TO MANIFEST  
AS THE WAVE LIFTS NORTH...LEADS TO SPLIT JET AND RAPID SFC  
CYCLOGENESIS ALONG THE EAST COAST. THE DIFFERENCES SEEM TO BE  
FROM ADDITIONS FROM THE TROPICAL CYCLONE/MOISTURE/INSTABILITY  
ADVECTION AND THE EFFECTS FROM CONVECTIVE PROCESSES AS THE LOW  
REACHES HUDSON CANYON/RIVER VALLEY ON MONDAY. THE 00Z NAM IS A  
SLIGHT BIT SLOWER AND LEADS TO INCREASED CONVECTIVE INFLUENCE AND  
STRONGER/TIGHTER ROTATION ALLOWING FOR A MORE WESTWARD TRACK THAN  
PRIOR RUNS AND APPEARS TO MATCH THE LEFT SIDE OF THE GUIDANCE  
REPRESENTATIVE: THE 12Z ECMWF. WHILE THE ECMWF HAS ALIGNED BETTER  
IN A TIGHTER ECENS ENSEMBLE SUITE IT REMAINS LEFT/DEEPER. THE 12Z  
CMC LOOKS QUITE GOOD THROUGH SUNDAY...BUT AS IT LIFTS NORTH  
INFLUENCE OF THE DEEPER TROPICAL REPRESENTATION FURTHER EAST AND  
THE APPROACHING SHORTWAVE OVER THE GREAT LAKES...STEALS THE VIGOR  
OF THE MAIN SHORTWAVE LEADING TO A WEAKER SURFACE REFLECTION AS  
WELL...WHICH LEADS TO A SLIGHTLY FASTER SFC SOLUTION. THE 00Z GFS  
TRENDED A LITTLE BIT WEAKER LOOKING SIMILAR TO THE CMC WHICH  
ALLOWS FOR A SLIGHTLY FASTER AND WESTERN TREND TO CONTINUE FOR THE  
PAST DAYS CYCLES. THE 00Z UKMET WHILE INITIALLY GOOD...IS A BIT  
SLOW LIFTING NORTH AND GIVEN THE NORTHERN STREAM SHORTWAVE OVER  
THE GREAT LAKES IS A BIT FAST...THE ORIENTATION IN TIMING LEADS TO  
A MORE PHASED ORIENTATION AND A CLEARLY DIFFERENT EVOLUTION FOR  
THE WAVE AS A WHOLE AND THEREFORE IS OUTRIGHT REJECTED FOR THIS  
RUN. ALL CONSIDERED A NON-UKMET BLEND IS PREFERRED AT INCREASED  
CONFIDENCE (SLIGHTLY ABOVE AVERAGE).  
 
07Z UPDATE: THE 00Z UKMET FAVORABLY TRENDED TOWARD THE GROWING  
CONSENSUS CENTERED NEAR THE 12Z ECENS MEAN/00Z GFS. THE 00Z GEFS  
MEAN AND A SLIGHTLY FASTER/FLATTER (ENTERING NEW ENGLAND) SOLUTION  
OF THE 00Z ECMWF FURTHER CEMENT THIS SOLUTION FROM A MASS  
PERSPECTIVE...LINGERING DIFFERENCE SEEM GREATEST ACROSS THE  
ATLANTIC (SOUTH OF LONG ISLAND) AS THE NAM/CMC BOTH HAVE STRONGER  
CONVECTIVE RESPONSES WHILE THE GFS/ECMWF FURTHER EXPAND THE DRY  
SLOT. A GENERAL MODEL BLEND COULD SUFFICE BUT GIVEN THE GROWING  
CONSENSUS THROUGH MUCH OF THE LOWER ATMOSPHERE INCLUDING QPF...AND  
STRENGTH OF ENSEMBLES SUGGEST A 00Z GFS/ECMWF BLEND.  
 
...SHORTWAVE NEAR S YUKON DIGGING INTO THE NORTHERN PLAINS BY  
SUNDAY AND EXPANDING INTO BROAD GLOBAL TROF ACROSS FROM NORTHEAST  
TO MIDWEST BY TUES...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
THE 12Z CMC AND 00Z GFS ARE A BIT FASTER WITH THE LEAD  
SHORTWAVE/HEIGHT FALLS CROSSING THE GREAT LAKES AIDING LARGER AND  
UPSCALE CYCLONIC DEVELOPMENT ACROSS SOUTHEAST CANADA BY  
MONDAY/TUESDAY...THOUGH THE OVERALL ORIENTATION/SHAPE OF THE BROAD  
TROF/SURFACE LOW AND FRONT ACROSS THE GREAT LAKES MATCHES WITH THE  
ENSEMBLE AND ECMWF/NAM SOLUTIONS TO KEEP WITHIN THE PREFERENCE.  
AS ALLUDED IN SECTION ABOVE...THE UKMET IS AN OUTLIER WITH THE  
OTHER GUIDANCE...MAINLY IN ORIENTATION OF THIS SYSTEM INTERACTING  
WITH NORTHEAST DEEP CYCLONE DEPICTING A MORE PHASED SOLUTION.  
THIS PHASED SOLUTION SLOWS THE EASTWARD PROGRESSION OF THE WAVE  
ALLOWING FOR DEEPER/SLOWER SFC CYCLONE AS WELL AS STALLED CAA  
DELAYING THE COLD FRONTS SOUTH-SOUTHEASTWARD PUSH...THOUGH THE 00Z  
NAM IS NOT TOO AFAR FROM THE LOWER LEVEL TIMING...WILL INCORPORATE  
THE NAM TO HANDLE THE UKMET SOLUTION WITHIN A NON-UKMET BLEND  
PREFERENCE. CONFIDENCE IS ABOVE AVERAGE AS THE OVERALL MODEL  
SPREAD AND EVOLUTION IS NOT SIGNIFICANTLY DIFFERENT.  
 
07Z UPDATE: THE 00Z UKMET STILL APPEARS A BIT SLOW CROSSING  
THROUGH THE GREAT LAKES AND WESTWARD BUT NO LONG HAS A PHASED  
ORIENTATION AS THE SHORTWAVE UNDERCUTS THE COASTAL SHORTWAVE INTO  
TUES...THIS ALLOWS FOR BETTER TIMING/AGREEMENT AS THE WAVE TAKES  
OVER THE CENTRAL HUB OF THE GLOBAL CYCLONE TUES WITH OTHER  
GUIDANCE...ENOUGH SO TO SUPPORT A GENERAL MODEL BLEND AT ABOVE  
AVERAGE CONFIDENCE.  
 
...BREAKDOWN OF WESTERN UPPER RIDGE AND MID-UPPER LEVEL LOW  
APPROACHING CALIFORNIA COAST BY SUNDAY AND THROUGH SOUTHWEST  
MON/TUES...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-NAM BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
MODELS CONTINUE TO SHOW SIMILAR EASTWARD TRACKING OF A FAIRLY  
SYMMETRIC CLOSED SHORTWAVE FEATURE REACHING THE SW CA COAST BY 00Z  
MON. LATITUDINAL DIFFERENCE APPEARS TO BE THE MAIN ISSUE WITH THE  
12Z UKMET NORTH AND THE 00Z NAM SOUTH. THE 12Z CMC IS A BIT  
WEAKER BUT TRACKS WELL WITH THE 00Z GFS/12Z ECMWF...EVEN AS THE  
GFS WEAKENS A BIT FASTER THAN THE ECMWF ACROSS S AZ/NM INTO TUES  
(AS THE ECMWF RETAINS A MORE COMPACT WAVE LONGER AS IT IS APT TO  
DO). WITH LITTLE CHANGE FOR THE 00Z GFS...FROM THE 12Z RUN...  
WILL CONTINUE A 00Z GFS AND 12Z ECMWF/CMC BLEND AT SLIGHTLY ABOVE  
AVERAGE CONFIDENCE.  
 
07Z UPDATE: THE 00Z UKMET SHIFTED AND THE 00Z CMC WAS A BIT DEEPER  
FURTHER SOLIDIFYING INITIAL PREFERENCE AND SUGGEST A NON-NAM BLEND  
WILL SUFFICE AT ABOVE AVERAGE CONFIDENCE.  
 
   
..WEAK SHORTWAVE ENTERING PACIFIC NORTHWEST LATE SUNDAY
 
DIGGING  
TOWARD CENTRAL COASTAL CA BY TUES...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
AS THE WESTERN RIDGE BREAKS DOWN SAT INTO SUNDAY A WEAK SHORTWAVE  
ROTATES INTO THE PACIFIC NORTHWEST SUNDAY AND BEGINS TO DROP SOUTH  
WITH SOME ELONGATION/PHASING WITH THE BASE OF THE LARGER SCALE  
TROF ROTATING THROUGH THE NORTHERN ROCKIES...THOUGH THE BULK OF  
THE ENERGY APPEARS TO TRY TO RECONSOLIDATE ALONG THE CA COAST WITH  
ASSISTANCE FROM UPSTREAM SHORTWAVE ENERGY OUT OF BC MON TOWARD  
TUES WITH THE 00Z NAM AND 12Z ECMWF LEADING THE WAY. THE 00Z GFS  
AND UKMET ARE A BIT MORE ELONGATED/SHEARED THROUGH THIS  
INTERACTION. THE 12Z CMC AND CYCLE TO CYCLE SPAGHETTI ANALYSIS  
TRENDS SEEM TO FAVOR THE ECMWF/NAM. SOLUTION AS SUCH A 00Z NAM AND  
12Z ECMWF/CMC BLEND IS PREFERRED FOR THIS WAVE. WHILE THE  
ORIENTATION/EVOLUTION MAY BE DIFFERENT THE OVERALL  
SPREAD/TIMING/SHAPE DO NOT PRESENT A LARGE SPREAD SUGGESTING  
CONFIDENCE SHOULD BE SLIGHTLY ABOVE AVERAGE FOR THIS BLEND.  
 
07Z UPDATE: THE 00Z UKMET TRENDED POSITIVELY TOWARD THE EVOLUTION  
OF THE INITIAL THINKING/PREFERENCE...THOUGH SIMILARLY THE  
ECMWF/CMC SHIFTED THE EVOLUTION A BIT SLOWER LIKE THE GFS/UKMET.  
OVERALL AS NOTED INITIALLY THE DIFFERENCES WERE MINOR. GIVEN THIS  
AND LIMITED OTHER SENSIBLE WX DIFFERENCES...A GENERAL MODEL BLEND  
APPEARS SUFFICIENT THOUGH CONFIDENCE REMAINS SLIGHTLY ABOVE  
AVERAGE GIVEN THE SLIGHT DIFFERENCES.  
 
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GALLINA  
 

 
 
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