069
FXUS10 KWNH 151627
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1226 PM EDT SUN SEP 15 2019
VALID SEP 15/1200 UTC THRU SEP 19/0000 UTC
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR
INGEST...
12Z MODEL EVALUATION WITH PREFERENCES AND FORECAST CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
...DEEP LATITUDE WESTERN TROF ENTERING THE WEST BY MONDAY;
REINFORCED BY CLOSED LOW LATE TUES...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z GFS AND 00Z ECMWF BLEND FIRST SHORTWAVE;
NON-UKMET FOR THE SECOND WAVE.
CONFIDENCE: AVERAGE
MODELS CONTINUE TO AGREE FAIRLY WELL IN THE APPROACH AND ENTRANCE
OF THE TROF INTO THE WEST COAST/N CA. HOWEVER, BY 48HRS THE
SPREAD IN THE MODELS MANIFESTS. THE 00Z UKMET, AS IT HAS BEEN FOR
DAYS, REMAINS FASTEST WITH LITTLE OTHER SUPPORT/REASONS. AS THE
SHORTWAVE CROSSES THE EASTERN SNAKE RIVER PLAIN, THE 12Z NAM
BECOMES MORE COMPACT AGAIN AND RAPIDLY DEEPENS FURTHER AS IT
STRETCHES ACROSS THE ROCKIES INTO EASTERN MT, AND IT CLEARLY IN AN
UNREALISTIC FEEDBACK DEEPENING THAT THE MODEL HAS A BIAS TOWARD.
THE 00Z CMC IS NOT TOO POOR, BUT STARTS TO EVEN LAG THE ECMWF
BECOMING SIGNIFICANT BY 72HRS TO INCLUDE. THERE IS A TYPICAL
SPREAD BETWEEN SLIGHTLY FASTER 12Z GFS AND 00Z ECMWF THAT HAS SPED
UP A BIT OVER PRIOR RUNS. AS SUCH, PREFERENCE IS 12Z GFS/00Z
ECMWF BLEND AT AVERAGE CONFIDENCE.
UPSTREAM, THE CLOSED LOW DROPPING INTO THE PACIFIC NW BY LATE
TUESDAY IS FAIRLY AGREEABLE WITH THE ONLY EXCEPTION BEING THE
UKMET WHICH AGAIN IS FAST, TOWARD 19.00Z, THE CMC AND ECMWF ARE A
BIT MORE SHARP WITH INCREASING POSITIVE TILT, BUT THIS DOES NOT
APPEAR TO BE OUT OF THE REALM OF BEST PROBABILITY GIVEN AVERAGE
DAY 3 SPREAD. AS SUCH NON-UKMET IS FINE FOR THIS PORTION OF THE
LARGER SCALE TROF.
...SOUTHWEST SHORTWAVE, MOVING THROUGH CENTRAL HIGH PLAINS INTO
NORTHERN PLAINS/MN BY TUESDAY...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z NAM/GFS AND 00Z ECMWF BLEND
CONFIDENCE: AVERAGE
THE 12Z GFS CONTINUES TO BE THE STRONGEST BRINGING THE WAVE
NORTH-NORTHEAST ACROSS THE SOUTHERN ROCKIES INTO THE CENTRAL HIGH
PLAINS LATE MONDAY AND UP THROUGH THE NORTHERN RED RIVER VALLEY BY
TUESDAY. WHILE, IT IS THE STRONGEST IT HAS TRENDED WEAKER THOUGH
IS STILL A BIT FASTER THAN THE ECMWF/CMC WHICH ARE TYPICAL OF BIAS
A BIT TOO SLOW. THE FASTER SOLUTION AND EARLIER RETURN OF
MOISTURE HELPS BREAK OUT CONVECTION EARLIER AS WELL, BUT THIS IS
SUPPORTED BY THE UKMET/NAM TO HAVE SOME CONFIDENCE ESPECIALLY NOW
THAT THE MAGNITUDE/COVERAGE IS REDUCED SLIGHTLY. THE 00Z CMC,
LIKE THE ECMWF IS SLOW, BUT IS ALSO A BIT TOO DRY, FAVORING THE
APPROACHING WESTERN TROF TO PROVIDE FORCING, SUGGESTING ITS
REMOVAL OR BLEND REDUCTION WOULD BE BEST. THE 00Z UKMET HAVING
ISSUES WITH A TOO FAST WESTERN TROF (SEE ABOVE), SO IT IS ALSO NOT
PREFERRED IN THIS BLEND. SO A GFS/NAM AND 00Z ECMWF BLEND IS
PREFERRED BUT SPLITTING THE TIMING DIFFERENCES. CONFIDENCE IS
AVERAGE GIVEN THE MODERATE SPREAD AND INFLUENCE OF THE APPROACHING
WESTERN TROF.
..WESTERN GULF OF MEXICO TUTT/SURFACE WAVE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z NAM/00Z ECMWF BLEND
CONFIDENCE: SLIGHTLY ABOVE AVERAGE
THE TUTT IS EXPECTED TO CONTINUE WEST ACROSS THE GULF WITH
EVENTUAL SUPPORT TO DEVELOP A WEAK SURFACE WAVE NEARING/SOUTHEAST
OF THE MOUTH OF THE RIO GRANDE MONDAY TO TUESDAY. THE 00Z UKMET
CONTINUES TO BE STRONGEST, FOLLOWED BY THE 00Z CMC AND SO GREATER
DEPTH/STEERING DRAWS IT NORTH. THE 00Z ECWMF IS A BIT SLOWER AND
WEAKER BUT IN LINE WITH THE RECENT FEW NAM RUNS, INCLUDING 12Z.
THE 12Z GFS IS A BIT STRONGER/SLOWER BUT REMAINS WEAKER AND GIVEN
DOWNSTREAM WEAKENING ACROSS NW MEXICO, SLIDES MORE WEST THAN OTHER
GUIDANCE. ALL CONSIDERED A BLEND OF THE 12Z NAM AND 00Z ECMWF IS
MIDDLE GROUND AND KEEPS WITH CONTINUITY, AND WHILE NOT ALIGNED
PERFECTLY, OTHER GUIDANCE PROVIDES CONFIDENCE TOWARD THIS BLEND
AND SO THE PREFERRED BLEND HAS SLIGHTLY ABOVE AVERAGE CONFIDENCE.
..TROPICAL STORM HUMBERTO
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: OFFICIAL NHC FORECAST
BEST PROXY: 06Z GFS/GEFS MEAN AND 00Z ECENS MEAN BLEND
CONFIDENCE: SLIGHTLY BELOW AVERAGE
HUMBERTO CONTINUES TO STRENGTHEN AND SURROUNDING STEERING
ENVIRONMENT SUGGESTS A STALLING AND SLOW EXPECTED TURN TOWARD THE
EAST IS WITHIN THE NEXT DAY. GUIDANCE CONTINUES TO SUGGEST A
SLOWING OVERALL. OVERALL, THE 06Z GFS, GEFS MEAN AND THE 00Z
ECENS MEAN ARE VERY CLOSE TO THE OFFICIAL NHC FORECAST. THE MAIN
TAKE AWAY THOUGH, IS THE NEWEST 12Z GUIDANCE CONTINUES TO SUPPORT
A SLOWING IN THE POST-2DAY FORECAST PERIOD WITH GREATER RIDGING
BUILDING TOWARD THE NORTHEAST. WHILE CLEARLY NOT TO THE MAGNITUDE
OF THE 00Z CMC THAT ACTUALLY SHOWS SIGNIFICANT SHEARING AND
SURFACE SLOWING TO THE EAST WITH MEDIUM RANGE SUGGESTING A TURN
BACK WEST. THERE ARE ABOUT 10-15% OF THE ECENS MEMBERS THAT ALSO
SUGGEST THIS EVENTUAL STALL DUE TO THE DEVELOPING BLOCK. SO THERE
IS STILL MODEST UNCERTAINTY AT 60-84HR PERIOD AND BEYOND. THE 00Z
ECMWF AND 12Z GFS ARE TIGHTLY PACKED NOW WITH THE 12Z NAM VERY
CLOSE ALL ABOUT 12HRS SLOW AND SLIGHTLY SOUTH OF THE OFFICIAL
TRACK, SO BEST PROXY TO THE 15Z NHC FORECAST IS THE 06Z GFS/GEFS
MEAN AND 00Z ECENS MEAN.
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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