177  
FXUS10 KWNH 171830  
PMDHMD  
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
229 PM EDT THU OCT 17 2019  
 
VALID OCT 17/1200 UTC THRU OCT 21/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z MODEL EVALUATION WITH PREFERENCES AND CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
RECORD DEEP SURFACE LOW IN NORTHEAST  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
VERY STRONG AGREEMENT EXISTS WITH RECORD DEEP CYCLONE IN THE  
NORTHEAST, ONLY THE 00Z CMC SLIGHTLY SHIFTS THE CENTER OF THE  
SURFACE LOW TOWARD THE ENHANCING TRIPLE POINT OVER THE ST.  
LAWRENCE WOBBLING IT FURTHER WEST. EACH OF THE OTHER GUIDANCE  
SHOWS THE STRONG TRIPLE POINT BUT STILL RETAINS THE OLDER OCCLUDED  
CENTER AS DOMINANT LIFTING THROUGH THE SEAWAY. THE CMC ROTATES  
BACK TO THE CONSENSUS AFTER 30HRS, SO A GIVEN THE OTHERWISE SUPER  
STRONG CONSENSUS THROUGH THE REMAINING MASS FIELDS, A GENERAL  
MODEL BLEND IS SUPPORTED AT ABOVE AVERAGE CONFIDENCE.  
 
DEEP LATITUDINAL WESTERN TROF PROGRESSING INTO THE PLAINS BY  
FRI...SPURRING NORTHERN PLAINS SURFACE LOW BY LATE THURS/FRI AND  
SOUTHERN PLAINS SURFACE LOW LATE FRI/SAT  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
MODELS CONTINUE TO SHOW SOLID AGREEMENT FOR THE INITIAL  
HEIGHT-FALLS/TROF CROSSING THE WEST TODAY AND DEVELOPING A  
NORTHERN PLAINS SURFACE WAVE THAT LIFTS NORTHEAST INTO CANADA.  
THE DEEP LATITUDE TROF, WILL ALSO SPUR A SECONDARY SURFACE WAVE  
ACROSS THE SOUTHERN PLAINS THAT WILL ELONGATE/SHEAR ALONG THE  
FRONTAL ZONE AS IT DROPS SOUTH AND THE BULK OF DRIVING ENERGY  
LIFTS NORTH. AS THE NORTHERN PORTION OF THE WAVE CROSSES CENTRAL  
CANADA, THE TRAILING TROF ACROSS THE GREAT LAKES SHOWS SOME MILD  
MID-LEVEL DIFFERENCE, BASED MAINLY ON TYPICAL SLOW BREAK DOWN OF  
THE ECMWF/CMC VS. THE FASTER BREAK DOWN IN THE UKMET/GFS. THIS IS  
NOT MUCH OF IMPORTANCE TO THE SENSIBLE WEATHER ACROSS THE GREAT  
LAKES, SO A GENERAL MODEL BLEND CAN BE SUPPORTED AT ABOVE AVERAGE  
CONFIDENCE.  
 
NW-SE ELONGATED SHORTWAVE ENTERING PAC NW SAT, CURLING INTO  
COMPACT DEVELOPING CLOSED LOW IN LEE OF CENTRAL ROCKIES BY SUN  
AFTERNOON...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND THROUGH 20.00Z  
12Z NAM/ECMWF/CMC BLEND THEREAFTER  
CONFIDENCE: AVERAGE  
 
19Z UPDATE: THE 12Z ECMWF/CMC BOTH TRENDED A BIT SLOWER EMERGING  
INTO THE CENTRAL HIGH PLAINS, PUTTING FURTHER DISTANCE IN TIMING  
AND EVOLUTION TO A MORE COMPACT CLOSED LOW WITH THE 12Z GFS AND  
EVEN THE 12Z NAM. THE 12Z UKMET ALSO FURTHER SLOWED, AND IN DOING  
SO SHIFTED SOUTH WITH THE TRACK/DEVELOPMENT OF THE WAVE AS WELL.  
SO WILL CONTINUE WITH THE INITIAL PREFERENCE INCLUDING THE SLOWING  
TREND WITH A 12Z NAM/ECMWF/CMC BLEND AFTER 20.00Z, THOUGH  
CONFIDENCE IS REDUCED SLIGHTLY TO AVERAGE AFTER 20.00Z.  
 
---PRIOR DISCUSSION---  
IN THE WAKE OF THE INITIAL HEIGHT-FALLS (SEE SECTION ABOVE), THE  
MID TO UPPER LEVEL FLOW IS FAIRLY FLAT AND VERY STRONG ACROSS THE  
PACIFIC. THE NOSE OF THE APPROACHING JET WILL HELP TO SPUR A  
STRONG SHORTWAVE THAT IS FAIRLY FLAT INITIALLY ENTERING THE  
PACIFIC NW BY SAT. GUIDANCE IS IN STRONG AGREEMENT IN  
PLACEMENT/TIMING OF THIS FEATURE, BUT AS THE SYSTEM CROSSES INTO  
THE WESTERN CONUS AND STARTS TO AMPLIFY (MAINLY THE UPSTREAM JET  
BUCKLES WITH A STRONG 150+ KT SPEED MAX ALONG THE SW PERIPHERY  
OF THE WAVE. AS IT CROSSES THE CENTRAL ROCKIES, TIMING ISSUES  
START TO OCCUR AS THE 12Z GFS JET ROUNDS THE BASE OF THE TROF  
ALLOWING FOR FASTER VORTEX ROLL-UP INTO THE CENTRAL PLAINS BY  
SUNDAY AFTERNOON, SPURRING A DEEPENING SURFACE CYCLONE. THE  
REMAINING GUIDANCE AND ENSEMBLES (INCLUDING A BULK OF THE GEFS  
MEMBERS) ARE SLOWER, WITH THE UKMET UNCHARACTERISTICALLY SLOW,  
PERHAPS TOO SLOW WITHIN THE OTHERWISE TIGHTER ENSEMBLE MEMBERS.  
AS SUCH AFTER 20.00Z, A 12Z NAM AND 00Z ECMWF/CMC BLEND IS  
PREFERRED AT SLIGHTLY ABOVE AVERAGE CONFIDENCE (PRIOR, A GENERAL  
MODEL BLEND IS SUFFICIENT).  
 
POTENTIAL TROPICAL CYCLONE SIXTEEN  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: PLEASE REFER TO 15Z NHC FORECAST  
BEST PROXY: 12Z GFS/UKMET UP TO 18.18Z; 12Z GFS/UKMET/ECMWF  
THEREAFTER  
 
19Z UPDATE: THE 12Z ECMWF SHOWS A BIT MORE REFLECTION OF THE  
INITIAL SURFACE WAVE EMERGING FROM THE CENTRAL GULF, BUT STILL HAS  
THE GREATEST HYBRID LOOK THROUGH THE VERTICAL DEPTH OF THE CYCLONE  
THAN THE GFS/UKMET. WHILE THE ECMWF REMAINS ON THE WESTERN SIDE  
OF THE GUIDANCE, A BLEND IN POSITION OF THE ECMWF WITH THE 12Z GFS  
AND 12Z UKMET (WHICH REMAINED FAIRLY CONSISTENT, PERHAPS A SHADE  
STRONGER) WILL BE THE CLOSEST PROXY TO THE OFFICIAL NHC  
TRACK/INTENSITY STARTING A BIT EARLIER AROUND 18.18Z...THOUGH A  
GFS/UKMET BLEND REMAINS BETTER IN LINE PRIOR TO 18.18Z.  
 
---PRIOR DISCUSSION---  
MOST OF THE GUIDANCE HAS FINALLY COME TO CONSENSUS WITH THE  
NORTHERN CLOSED LOW ACROSS TX IN TERMS OF PLACEMENT, DEPTH, AND  
SHAPE TO HAVE BETTER CONFIDENCE IN THIS PORTION OF THE STREAM.  
THE TROPICAL/SUBTROPICAL STREAM IS STILL A BIT ELONGATED AND  
HIGHLY DEPENDENT ON CONVECTIVE ENHANCEMENT TO THE MASS FIELDS, SO  
THERE REMAINS MODERATE SPREAD. THE 12Z GFS AND 00Z UKMET ARE WELL  
TIMED TO THE OFFICIAL NHC FORECAST EVEN EARLY IN THE FORECAST  
PROCESS BUT STILL ON THE SOUTHEAST SIDE OF THE OFFICIAL TRACK.  
THE 00Z ECMWF SHOWS STRONGER/TIGHTER BINARY INTERACTION BETWEEN  
THE NORTHERN AND TROPICAL STREAMS DEEPENING THE SURFACE WAVE VERY  
NEAR THE MOUTH OF THE MS RIVER BY 19.00Z WHICH IS NW OF THE TRACK.  
AFTER 19.00Z, THE OFFICIAL FORECAST REMAINS DOMINANTLY NEAR THE  
GFS/UKMET WITH SOME INCREASING WEIGHTING TOWARD THE ECWMF  
ESPECIALLY AS THE WAVE REACHES NC/EAST COAST AT 21.00Z. THE 12Z  
NAM REMAINS WEAK AND SLOW, AND CMC IS ALSO WEAK AND WELL SOUTH OF  
THE TRACK TO NOT BLEND EITHER. SO, INITIALLY THE BEST PROXY TO  
THE 15Z NHC FORECAST IS A 06Z GFS/00Z UKMET BLEND UP TO 19.06Z,  
THEN INCORPORATE INCREASING INFLUENCE/PERCENTAGE TO THE 00Z ECMWF  
AFTER 19.06Z.  
 
MODEL TRENDS AT WWW.WPC.NOAA.GOV/HTML/MODEL2.HTML  
500 MB FORECASTS AT WWW.WPC.NOAA.GOV/H5PREF/H5PREF.SHTML  
 
GALLINA  
 

 
 
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