300
FXUS10 KWNH 181835
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
234 PM EDT FRI OCT 18 2019
VALID OCT 18/1200 UTC THRU OCT 22/0000 UTC
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR
INGEST...
12Z MODEL EVALUATION WITH PREFERENCES AND CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
NORTHERN STREAM SHORTWAVES ENTERING THE WEST EJECTING INTO
NORTHERN AND SOUTHERN PLAINS...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND THROUGH 54 HOURS;
12Z UKMET/ECMWF/GEFS AND 00Z ECENS MEAN BLEND
THEREAFTER
CONFIDENCE: SLIGHTLY ABOVE AVERAGE TO ABOVE AVERAGE FOR LEAD WAVE
AVERAGE AFTER 54HRS
19Z UPDATE: NO CHANGE ON THE LEADING SHORTWAVE(S) IN EITHER STREAM
AND CONTINUATION WITH GENERAL MODEL BLEND REMAINS.
FOR THE DEVELOPING PLAINS LOW ON DAY 3, THE 12Z UKMET SLOWED A
TAD, TOWARD THE 06Z GEFS AND WITH THE 12Z GEFS SHIFTING A BIT
FASTER THAN THE 06Z GEFS, THERE IS STILL SOLID AGREEMENT TO KEEP
BETTER CONFIDENCE AWAY FROM THE FASTER NAM/OPERATIONAL GFS. THIS
WAS FURTHER ENHANCED AS THE 12Z ECMWF TRENDED FASTER AND VERY
CLOSE TO THE 00Z ECENS. SO THERE IS EVIDENCE, BOTH OF THESE
OPERATIONAL GUIDANCE MEMBERS ALONG WITH THE ENSEMBLE MEANS WILL BE
FRUITFUL AS PREFERENCE BRINGING CONFIDENCE BACK TO AVERAGE AFTER
54HRS. FOR NOTE: THE 12Z CMC REMAINED SLOW AND LOOKS LIKE A
CLEAR OUTLIER NOW WITHOUT ITS ECMWF PAIR.
---PRIOR DISCUSSION---
GOES-WV SUITE DENOTES A SHARP AND DEEP LATITUDE TROUGH ADVANCING
FROM SW SASKATCHEWAN SOUTH THROUGH UT/AZ ADVANCING WITH MODEST
PACE. A SURFACE TROF WITH MULTIPLE WAVES ACROSS S CANADA AND THE
DAKOTAS WILL SHARPEN/FOCUS TO THE NORTH AS THE NORTHERN PORTION OF
THE TROF BREAKS FROM THE SOUTHERN. ALOFT THE CMC, MORE SO THAN
THE ECMWF, ARE IN A TYPICAL SLOWER POSITION AND SO ARE A BIT MORE
AMPLIFIED LIFTING THROUGH THE GREAT LAKES BUT WITH LIMITED
SENSIBLE WEATHER AFFECTS TO BREAK FROM A GENERAL MODEL BLEND FOR
THIS PORTION OF THE WAVE.
AS THE SOUTHERN PORTION OF THE TROF EMERGES, EARLY SATURDAY, THE
FRONTAL ZONE WILL PRESS EASTWARD INTO AR/E TX BY LATE EVENING WITH
THE GFS A BIT FASTER THAN THE ECMWF BUT NOT TO TREMENDOUS NEGATIVE
EFFECT GIVEN HOW WEAK THE REMAINING FORCING IS RELATIVE TO NORTH.
STILL THE UPPER LEVEL SHORTWAVE WILL HELP TO KICK OUT THE COMBINED
BAROCLINIC/POTENTIAL TC 16 WITH GENERAL WEAKENING THROUGH THE TN
VALLEY. SO LIKE THE NORTH, A GENERAL MODEL BLEND CAN BE SUPPORTED
FOR THIS WAVE.
UPSTREAM, HOWEVER, THE NEXT STRONGER SHORTWAVE ALONG THE CYCLONIC
ROTOR OF A VERY STRONG/BROAD PACIFIC JET, IS ALREADY PRESSING
HEIGHT-FALLS WITH INCREASED WAVY NATURE TO THE PATTERN ENTERING
THE UPPER SNAKE RIVER/CENTRAL ROCKIES BY 20.00Z. TYPICAL TIMING
ISSUES ARE ALREADY STARTING TO MANIFEST BY THIS TIME, WITH THE 12Z
GFS AND 00Z UKMET OUTPACING THE 00Z ECMWF/CMC. HOWEVER, THE GEFS
MEMBERS ARE SLOWER THAN THE OPERATIONAL AND THE ECENS ARE FASTER
AND THIS WILL BE KEY AS THE NOSE OF THE DIFFLUENT PATTERN AHEAD OF
THE TROF REACHES THE FRONT RANGES OF THE ROCKIES. VORTICAL
STRETCHING COMBINED WITH THE FAVORABLE UPPER PATTERN LEADS TO
RAPID SURFACE CYCLOGENESIS IN THE FASTER SOLUTIONS OF THE GFS, BUT
THE SLIGHTLY SLOWER NAM, UKMET ARE A BIT MORE REASONABLE RELATIVE
TO THE GEFS THAN THE OPERATIONAL GFS. BY 21.00Z, THE ECMWF IS
WELL TOO SLOW AND EMERGES MORE ELONGATED NORTH SOUTH DUE TO
BROADER ZONE OF VORTICITY STRETCHING OUT OF THE TERRAIN. THIS
LEADS TO ABOUT A 6HR DELAY EVEN COMPARED TO YESTERDAY'S 12Z ECMWF
RUN AND TWO MOST RECENT ECENS MEANS; A TYPICAL NEGATIVE SIGN FOR
THE OPERATIONAL ECMWF. THOUGH IT IS PAIRED WITH THE CMC, WILL BE
FAVORING A GEFS/ECENS MEAN BLEND AFTER 20.18Z WITH SLIGHTLY BELOW
AVERAGE CONFIDENCE DUE TO THE LARGER THAN NORMAL TIMING
DIFFERENCES AND THEIR EFFECTS ON THE CYCLONE DEVELOPMENT.
TROPICAL STORM NESTOR (FORMER PTC SIXTEEN)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: SEE LATEST NHC ADVISORY
BEST PROXY: 12Z UKMET/ECMWF
19Z UPDATE: THE ECMWF AND CMC BOTH HAVE LATCHED ONTO THE
CONVECTIVE CENTER OF NESTOR NEAR THE UKMET, AS THE SYSTEM GOES
EXTRATROPICAL CROSSING THE SOUTHEAST, THE GFS BREAKS A BIT FAST
COMPARATIVELY, AND WHEN THE UKMET/ECMWF SLOW TO MATCH THE 15Z NHC
FORECAST BEST. SO NOW, BEST PROXY IS A 12Z UKMET/ECMWF BLEND,
THOUGH ONLY THE NAM IS A SIGNIFICANT OUTLIER FROM THE
DETERMINISTIC GUIDANCE SUITE.
---PRIOR DISCUSSION---
12Z NAM/06Z GFS AND 00Z ECMWF/CMC ALONG WITH A PLETHORA OF WRF
HI-RES CAMS APPEAR TO BE FAVORING THE BAROCLINIC DEVELOPMENT OF
THE CONVECTIVE ENVIRONMENT (STRONGER THUNDERSTORMS/CLUSTERING
ALONG THE NORTHERN GULF FRONTAL ZONE) OVER THE CONVECTIVE
COMPLEX/CONFLUENT SURFACE TROF/EFFECTIVE COLD FRONT SOUTH OF THE
DEVELOPING SURFACE LOW. THIS IS OPPOSED BY THE UKMET AND THE 12Z
HRRR/EXP. HRRR. THE LATTER APPEAR TO HAVE A MORE REALISTIC
DEPICTION OF THE CURRENT CONVECTIVE ENVIRONMENT AS WELL AS THE
INSTABILITY FIELD OVER THE FORMER SOLUTIONS EVEN THOUGH THEY ARE
LESS NUMEROUS IN THE OVERALL SUITE. YET, THE SURFACE
CIRCULATION/CENTER CONTINUES TO STRUGGLE TO COME TOGETHER (HENCE
STILL PTC) WHICH IS IS COUNTER TO INITIALIZATION OF MOST OF THE
GUIDANCE WHICH HAS FORMED A CONSISTENT SURFACE LOW, TRACKING IT
NORTHEAST. THE 12Z GFS APPEARS TO BE COMING TO A COMPROMISE NOW
INITIALLY FAVORING THE DEEPER CONVECTION THAT IS ONGOING AT
INITIALIZATION RELATIVE TO THE 06Z RUN. SO EVEN THOUGH THE
CLUSTERING IS TIGHTENING IN THE GUIDANCE, THE EVOLUTION PATH IS
QUITE UNCERTAIN SO CLOSE MONITORING/CHANGES IN OBSERVATIONS MAY
KEY TO DETERMINING THE BEST SOLUTION.
CURRENTLY, THE 15Z NHC FORECAST TRACK BEST PROXY APPEARS TO BE
SOMETHING CLOSER TO A BLEND OF THE 06Z GFS AND THE 00Z ECMWF,
THOUGH THE 12Z GFS REMAINS A BIT FASTER INITIALLY AND LOOKS A BIT
BETTER TO BLEND WITH THE 00Z ECWMF AS A PROXY TO THE 15Z FORECAST
THAN THE 06Z ESPECIALLY AFTER CROSSING THE SOUTHEAST INTO THE
WESTERN ATLANTIC.
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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