561
FXUS10 KWNH 131825
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
224 PM EDT FRI SEP 13 2019
VALID SEP 13/1200 UTC THRU SEP 17/0000 UTC
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR
INGEST...
12Z MODEL EVALUATION WITH PREFERENCES AND FORECAST CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
..CONUS
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
EXCEPTIONS: NON-UKMET IN PACIFIC NORTHWEST
12Z GFS/ECWMF BLEND IN WESTERN/CENTRAL GULF COAST
CONFIDENCE: ABOVE AVERAGE
19Z UPDATE: THE 12Z UKMET APPEARS TO HAVE SLOWED A BIT IN THE
PACIFIC NORTHWEST THROUGH DAY 2, BUT STILL JUMPS A SLIGHT EAST OF
THE INCREASING CLUSTERING (THOUGH ECMWF/CMC ARE A BIT FURTHER
SOUTH AND SLOWER THAN THE GFS). OVERALL, A NON-UKMET BLEND REMAINS
IN PLACE IN THIS REGION. ELSEWHERE, SIMILAR EVOLUTION WITH THE
12Z UKMET/CMC/ECWMF/GEFS TO SUPPORT INITIAL PREFERENCE (WITH 12Z
ECMWF INCLUDED ALONG WESTERN GULF COAST OVER THE 00Z RUN).
---PRIOR DISCUSSION---
FOR THE CONUS, THE BROAD CYCLONE ACROSS THE UPPER GREAT LAKES
CONTINUES TO SHIFT NORTHEAST INTO CANADA WITH LITTLE MODEL
VARIATION, THE UPSTREAM SHORTWAVE TRACKING ALONG THE US/CANADA
BOARDER HAS COME INTO GOOD AGREEMENT AS WELL, WITH SOME SMALL
DEPTH, MINOR TIMING DIFFERENCES AS IT BROADENS THE LARGER SCALE
TROF (WITH THE PRECURSORY SYSTEM) CROSSING NEW ENGLAND INTO
SUNDAY. AGAIN, HERE THE GUIDANCE IS SOLID ENOUGH FOR A GENERAL
MODEL BLEND AT ABOVE AVERAGE CONFIDENCE.
FURTHER WEST, THE GULF OF ALASKA BROAD CLOSED LOW SWINGS FROM A
LATITUDINAL ORIENTATION TOWARD A MORE NORTH-SOUTH ONE, STRETCHING
WITH A BASE SHORTWAVE ENTERING N CA TOWARD LATE SUNDAY EARLY
MONDAY. ONLY THE UKMET BEING INITIALLY FAST, FAVORING THE
NORTHERN PORTION OF THE TROF OFFSETS AGAINST THE OTHER GUIDANCE,
INCLUDING ENSEMBLE SUITE. THIS LOOKS FAIRLY STRAIGHT FORWARD WITH
SOME CONTINUITY THROUGH THE RECENT ENSEMBLE TRENDS, SO ABOVE
AVERAGE CONFIDENCE CAN BE HAD WITH THIS NON-UKMET BLEND IN THE
WEST.
CONVECTIVE COMPLEX OVER THE NORTHERN SIERRA MADRE OCCIDENTAL ON
FRIDAY NIGHT INTO SATURDAY, LIFTS SLIGHTLY NORTH AS THE ELONGATED
SUBTROPICAL RIDGE AT OR ALONG 32N BREAKS DOWN. THE 12Z GFS
CONTINUES TO BE THE MOST ROBUST WITH THE WAVE, BUT BY SUNDAY,
OTHER GUIDANCE SUPPORTS THE EVENTUAL UPSCALE GROWTH ACROSS THE
SOUTHWEST. WHILE, THE GFS WILL REMAIN STRONGER/DEEPER THROUGH THE
FORECAST PERIOD, BUT GIVEN THE APPROACHING WESTERN TROF, IT ALSO
LIFTS A BIT FASTER NORTH WITH GREATER MOISTURE FLUX INTO THE GREAT
BASIN AND MAYBE EVEN THE EASTERN SNAKE RIVER PLAIN BY LATE IN THE
FORECAST PERIOD. GIVEN THE GFS IS SLIGHTLY FASTER WITH THE
WESTERN TROF (IN A TYPICAL TIMING DIFFERENCE WITH THE ECMWF/CMC)
AND SUPPORTED BY THE NAM; WPC WILL EMPLOY A TYPICAL BLEND TO SLOW
THE GFS AND SPEED UP THE ECMWF/CMC. WHILE THE UKMET, HAS ISSUES
IN THE NORTHERN STREAM, THIS WAVE IS WELL TIMED AND HAS SIMILAR
STRENGTH TO THE ECWMF...TO HAVE SOME CONFIDENCE IN USING IT IN THE
SW.
..POTENTIAL TROPICAL CYCLONE NINE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: OFFICIAL NHC FORECAST
BEST PROXY: NON-NAM OR
00Z UKMET/ECMWF THRU 15.00Z, 12Z CMC/GFS AFTER
CONFIDENCE: BELOW AVERAGE
19Z UPDATE: THE 12Z UKMET AND ECMWF ARE STEADFAST WAITING FOR
CONVECTION TO SPUR THE SURFACE WAVE, WHILE CONVECTION IS
ORGANIZING BETTER NOW, THE DELAY IN DEVELOPMENT SLOWS THE TRACK
NORTH AND TURNS BACK TOWARD THE SE FURTHER AWAY FROM THE OFFICIAL
FORECAST TRACK. THE 12Z CMC IS ON THE FLIP-SIDE NOT REALLY
DEVELOPING THE SURFACE REFLECTION UNTIL 15.00Z NW OF GRAND BAHAMA
AND TAKES IT NORTH AND ALONG THE OFFICIAL TRACK THE BEST, BUT IS
VERY WEAK OVERALL, EVEN COMPARED TO THE GFS. SO THERE IS NO BEST
PROXY TO THE NHC FORECAST, THOUGH IT GETS CLOSEST TO THE 12Z CMC
AFTER 15.12Z.
---PRIOR DISCUSSION---
THE APPEARANCE OF PTC NINE CONTINUES TO BE HIGHLY TILTED WITH A
DEVELOPING MID-LEVEL CIRCULATION FURTHER EAST OF THE BAHAMIAN
OUTER CHAIN. THE 00Z UKMET/ECMWF CONTINUE TO LATCH ONTO THIS MLC
AND UTILIZE CONVECTIVE PROCESSES TO STRETCH TO THE SURFACE. THIS
IS INITIALLY IN LINE WITH THE 15Z OFFICIAL NHC FORECAST. THE 00Z
CMC CONTINUES TO SUGGEST THE APEX OF THE SURFACE WAVE/SURFACE LOW
WILL TRACK THROUGH THE CENTRAL BAHAMAS CLOSER TO FL COAST
REMAINING WEAK. THE 12Z GFS SHIFTED EAST FROM PRIOR RUNS, AND
LOOKS SIMILAR TO THE CMC...BOTH WEST AND FURTHER FROM THE NHC
FORECAST AT LEAST INITIALLY (THROUGH 15.12Z) THE 12Z NAM,
CONTINUES TO BE THE MOST VERTICALLY TITLED, AND SHIFTED WEST
THROUGH THE SOUTHERN FL PENINSULA WELL AWAY FROM THE OFFICIAL NHC
FORECAST AND IS DISREGARDED AS A PROXY SOLUTION.
BY 15.12Z, NORTHERN INFLUENCES FROM THE LINGERING FRONTAL ZONE
COME INTO PLAY AND THE CMC/GFS BOTH INTENSIFY FROM SOME BAROCLINIC
INFLUENCES AND WHILE STILL LEFT OF THE OFFICIAL TRACK BECOME MUCH
CLOSER TO IT AFTER 15.12Z EVENTUALLY TURNING EASTWARD...WITH THE
GFS A TAD STRONGER AND FASTER THAN THE CMC. THE UKMET, ECMWF BOTH
START MUCH DEEPER AND MORE CONCENTRIC...WHICH GIVEN THE SHEAR
ENVIRONMENT WOULD SUGGEST A STRONG CONVECTIVE CORE. GIVEN
UPWELLING FROM DORIAN, THERE IS SUFFICIENT HEAT BUT MAY NOT BE
ENOUGH TO BE AS STRONG AS THESE GUIDANCE MEMBERS REQUIRE. SO, A
NON-NAM BLEND IS BEST PROXY OVERALL, BUT STARTING WITH THE 00Z
ECMWF/UKMET UNTIL ABOUT 16.00Z THEN SHIFTING TOWARD A 00Z CMC/12Z
GFS AFTERWARD IS LIKELY TO BE A STRONGER PROXY TO THE OFFICIAL
FORECAST. CONFIDENCE REMAINS SLIGHTLY BELOW AVERAGE IN THIS PROXY
TO THE NHC FORECAST TRACK GIVEN THE BROAD SPREAD AND CONTINGENCY
ON PERSISTENT CONVECTIVE PROCESSES TO DEVELOP THE SURFACE LOW.
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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