060
FXUS10 KWNH 031833
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
233 PM EDT TUE SEP 03 2019
VALID SEP 03/1200 UTC THRU SEP 07/0000 UTC
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR
INGEST...
12Z MODEL EVALUATION, CONFIDENCE, AND PREFERENCES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
..OVERALL PATTERN ACROSS THE CONUS
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
EXCEPTION: 12Z NAM/GFS/ECMWF IN NORTH PACIFIC AND NORTHERN ROCKIES
CONFIDENCE: SLIGHTLY ABOVE AVERAGE
19Z UPDATE: THERE IS INCREASED AGREEMENT IN THE NORTHWEST FLOW,
TIMING OF SHORTWAVE AND NOSE OF THE UPPER LEVEL JET, TO KEEP AN
GENERAL MODEL BLEND AS THE ECMWF/CMC SPED UP WITH THE INITIAL WAVE
AND THEREFORE SLOWED THE NOSE OF THE JET. SO A GENERAL MODEL
BLEND REMAINS PREFERRED, THOUGH THOSE SMALL TIMING RUN TO RUN
VARIATIONS CONTINUE TO PLAY A KEY ROLE FOR DORIAN.
THE UKMET SLOWED OFF SHORE, BUT STILL REMAINS WELL EAST OF THE
OTHER GUIDANCE, AND WITH A SLOWER CMC LIFTING INTO THE PACIFIC NW
AND INTO THE ROCKIES BY DAY 3...THINK A REMOVAL OF THE CMC FOR
THIS WAVE IS A GOOD IDEA AS WELL. AS SUCH WILL EXPAND THE
EXCEPTION TO INCORPORATE BOTH THE OFFSHORE SYSTEM, AS WELL AS, THE
SYSTEM LIFTING ACROSS THE PACNW/N ROCKIES D3 WITH A 12Z
NAM/GFS/ECMWF BLEND.
---PRIOR DISCUSSION---
BROAD GLOBAL TROF ANCHORED IN S HUDSON BAY CONTINUES SLOW SHIFT
NORTH AND EAST, ESPECIALLY AFTER EMBEDDED SHORTWAVE AND ASSOCIATED
DEEP SURFACE WAVE CROSS THROUGH THE GREAT LAKES TODAY INTO SE
CANADA BY EARLY THURS WITH COLD FRONT PRESSING THROUGH NEW
ENGLAND. THIS IS WELL AGREED UPON, WITH EXCEPTION OF THE 12Z NAM
STILL LINGERING A DEEPER TROF THROUGH THE MID-ATLANTIC AROUND
60HRS...THIS IS LIKELY LEADING TO THE NAM BREAKING AWAY FROM THE
CONSENSUS WITH DORIAN AFTER THIS TIME PERIOD.
AFTERWARD, THE STRONG GULF OF AK JET AND CLOSED LOW/SHORTWAVE
ENTERING SW CANADA CURRENTLY, WILL INTERACT BUT LEAD TO FAIRLY
FLAT NORTHWESTERLY FLOW ACROSS CENTRAL CANADA. THE PACIFIC
SHORTWAVE WILL LEAD THE NOSE OF THE 250MB JET, TOO FAR AND
SHEAR/WEAKEN INTO THE NW GREAT LAKES BY LATE THURSDAY. TYPICAL
ALIGNMENT OCCURS WITH THIS WAVE WITH THE ECMWF/CMC SLOWER/LAGGING.
HOWEVER, BY SHORTENING THE WAVE LENGTH TO THE NOSE OF THE JET,
THIS LEADS THE ECMWF/CMC TO BE FASTER WITH THE NEXT WAVE AND
SLIGHTLY DAMPENED INTO THE CONFLUENT FLOW RELATIVE TO THE 12Z
NAM/GFS AND UKMET. THESE ARE VERY SUBTLE TIMING DIFFERENCES AND
ARE VERY DIFFICULT TO LOCK DOWN, AS NOTED BY THE RUN TO RUN
VARIATION. ADMITTEDLY, THIS HAS HIGH IMPACT TO THE TRACK OF DORIAN
AS WELL. BOTH THE NAM/GFS ARE SLIGHTLY STRONGER WITH THE UPPER
JET MAKING THE ECMWF LOOK OF OF SORTS, STILL THIS IS LOWER IMPACT
TO QPF/SENSIBLE WEATHER ACROSS THE NORTHERN TIER INTO THE GREAT
LAKES TO SUPPORT A GENERAL BLEND HERE (SEE PROXY TO NHC FOR DORIAN
BELOW).
ACROSS THE NORTHWEST, HOWEVER, THERE IS SUFFICIENT SPREAD BUT NOT
ASHORE EVEN THROUGH 84HRS. THE REMAINING CLOSED LOW THAT IS
OFFSHORE BY THURSDAY, CONTINUES TO LIFT/SHEAR INTO THE ROCKIES
RIDGE BREAKING IT DOWN A BIT BY FRIDAY. THE 12Z NAM/ECMWF ARE
SLIGHTLY STRONGER BY 84HRS IN LINE WITH THEIR BIASES (EC-SLOW AND
NAM-STRONG BY END OF D3) BUT WITH LITTLE NEGATIVE AFFECT FOR QPF
ACROSS THE ROCKIES. THE SPREAD, IS THE DEEP LATITUDE TROF
APPROACHING OUT OF THE GULF OF AK, THAT KICKS THE PRECURSORY WAVE
INTO THE RIDGE, AND THE 00Z UKMET IS A CLEAR FAST OUTLIER, EARLY.
EVENTUALLY, THE CMC IS STRONGER, MORE COMPACT FURTHER NORTH AND
SHIFTS EASTWARD WITH THE TROF AXIS. THIS ALSO MAKES IT LESS
PREFERABLE, SO WOULD SHIFT TO A 12Z NAM/GFS AND 00Z ECMWF BLEND IN
THE PACIFIC FOR THE END OF D2 INTO D3. THOUGH ELSEWHERE, A
GENERAL MODEL BLEND CAN BE EMPLOYED WITH SLIGHTLY ABOVE AVERAGE
CONFIDENCE (AVERAGE OVER THE GREAT LAKES INTO D3 GIVEN RUN TO RUN
VARIANCE AND CRITICAL IMPORTANCE OF TIMING)
..HURRICANE DORIAN
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PLEASE REFER TO THE OFFICIAL NATIONAL HURRICANE CENTER FORECAST
TRACK
19Z UPDATE: WITH THE 12Z UKMET, CMC, ECMWF AND GEFS ALL CONTINUE
TO TREND SLOWER AND SLIGHTLY WEST OF THE OFFICIAL TRACK. THE
ECMWF REMAINS SLOWEST AND FURTHER WEST BEFORE MAKING THE TURN
NORTHEAST, THE CMC SLOWED SIGNIFICANTLY (COMPARED TO THE 12Z RUN)
AND IS NOW BETWEEN THE ECMWF AND GFS AND AWAY FROM BEST PROXY FOR
15Z NHC FORECAST. THE UKMET SLOWED THE LEAST AND MATCHES WELL
WITH THE GFS, BOTH STILL SLOWER LIFTING THE CYCLONE NORTHEASTWARD.
SO THE BEST PROXY REMAINS A 06Z GFS/00Z CMC BLEND, BUT WOULD
SUSPECT A SLOWING WITH THE 21Z FORECAST...PLEASE REFER TO NHC
OFFICIAL PRODUCTS FOR GREATEST DETAILS/FORECAST PREFERENCES.
---PRIOR DISCUSSION---
INITIALLY, AS DORIAN TRACKS NNW, THE GUIDANCE IS FAIRLY WELL
CLUSTERED TO THE OFFICIAL NHC TRACK. BUT AS IT TURNS AND LIFTS
PARALLEL TO THE CAROLINA COASTS, TIMING DIFFERENCES BEGIN TO
MANIFEST WITH THE 12Z NAM CONTINUING TO ACCELERATE WELL OUT OF
PLACE OF THE OTHERWISE SOLID CONSENSUS. HOWEVER, THE 00Z ECMWF
EVENTUALLY BREAKS TOO SLOW AFTER 60HRS AS WELL...THAT BOTH ARE NOT
IN A BEST PROXY. THE UKMET REDEVELOPS MUCH DEEPER AND SLOWS
RELATIVE TO THE OFFICIAL TRACK FORECAST ABOUT 72-84HRS; THE 12Z
GFS SLOWED A BIT AS WELL DRIVEN BY A STRONGER JET AXIS OVER THE
APPALACHIANS FOR A LONGER PERIOD OF TIME EVEN WITH THE APPROACH OF
THE NORTHERN STREAM SHORTWAVE/JET ENERGY. THIS SEEMS QUITE
FAVORABLE BUT SLOWS THE TRACK OF DORIAN OFF THE OFFICIAL TRACK
FROM NHC. SO THE 06Z GFS AND 00Z CMC ARE CLOSEST IN PROXY TO THE
TRACK... BUT INCLUSION OF THE 00Z UKMET AND 12Z GFS SEEMS A GOOD
IDEA GIVEN THE APPROACH OF THE SHORTWAVE/BAROCLINIC INFLUENCES
TOWARD 84HRS.
..TROPICAL STORM SEVEN (FERNAND).
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PLEASE REFER TO THE OFFICIAL NATIONAL HURRICANE CENTER FORECAST
TRACK
19Z UPDATE: A VERY SLIGHT NORTHWARD SHIFT WAS NOTED WITH ALL 3
NON-NCEP GUIDANCE MEMBERS, SO THE UKMET NOW IS CLOSEST PROXY TO
THE OFFICIAL 15Z FORECAST, BUT THE PROXIMITY TO THE NAM, GFS AND
ECMWF ARE GOOD ENOUGH. THE CMC IS THE OUTLIER AND SO BEST PROXY
COULD BE THE 12Z UKMET OR NON-CMC BLEND.
---PRIOR DISCUSSION---
NHC STARTED CLASSIFYING THE WEST GULF SYSTEM AT 09Z. THE 15Z OF TD
SEVEN IS FORECAST ALONG THE NORTHERN PERIPHERY OF THE MAIN
DETERMINISTIC GLOBAL GUIDANCE, CLOSEST TO THE 12Z NAM AND 00Z
UKMET. HOWEVER, THE NAM HAS A NORTHWARD BIAS WITH THE EXTENDING
THE 850-7H TROF BRINGING QPF MUCH FURTHER NORTH THAN EXPECTED,
OPPOSED BY THE 12Z NAM-CONEST, WHICH IS MUCH CLOSER TO THE WPC
PREFERENCE WITH RESPECT TO QPF IN TX. THE 12Z GFS SHOWS SIMILAR
NORTHWARD SHIFT COMPARED TO 00Z RUN AND JUST A FEW MILES SOUTH OF
THE OFFICIAL TRACK (ESPECIALLY THROUGH LANDFALL). SO FOR
WINDS/MASS...THE BEST PROXY IS THE 12Z NAM-CONEST/GFS AND 00Z
UKMET FOR THE 15Z FORECAST, HOWEVER, THE NAM MAY WORK IN THE MASS
FIELDS, IF ONE DOES NOT HAVE THE CONEST TO BLEND.
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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