620
FXUS10 KWNH 151842
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
241 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/ECMWF/CMC BLEND FIRST SHORTWAVE;
GENERAL MODEL BLEND FOR THE SECOND.
CONFIDENCE: SLIGHTLY ABOVE AVERAGE
19Z UPDATE: THE 12Z ECMWF/CMC BOTH TRENDED EVER SO SLIGHTLY FASTER
(MORE SO FOR THE CMC), TO MATCH THE GFS FAIRLY WELL. THIS
PROVIDES ADDITIONAL CONFIDENCE IN A 12Z GFS/ECMWF/CMC BLEND AT
SLIGHTLY ABOVE AVERAGE CONFIDENCE FOR THIS INITIAL SHORTWAVE. THE
UKMET REMAINED A BIT TOO FAST AND DEEP TO INCORPORATE AT THIS
TIME.
THE SECOND, CLOSED LOW, CONTINUES TO SHOW MUCH BETTER OVERALL
AGREEMENT WHICH INCLUDES THE UKMET. HOWEVER, THE UKMET IS
GENERALLY A BIT WEAKER RELATIVE TO THE REMAINING DETERMINISTIC
GUIDANCE, BUT STILL IS A HIGHER QPF PRODUCER THOUGH IN SIMILAR
PLACES/TIMING WITH OTHER SOLUTIONS TO SUPPORT ITS INCLUSION FOR
THIS WAVE. SO GENERAL MODEL BLEND IS PREFERRED FOR THIS SYSTEM.
---PRIOR DISCUSSION...
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: GENERAL MODEL BLEND
CONFIDENCE: SLIGHTLY ABOVE AVERAGE
19Z UPDATE: THE 12Z ECMWF, CMC AND UKMET ALL TRENDED A BIT
STRONGER AND WITH SIZABLE INCREASE IN FORWARD SPEED PROGRESSING
INTO THE NORTHERN PLAINS/MN. THIS PUTS IT ON PAR WITH THE GFS/NAM
AND PROVIDES SIGNIFICANTLY GREATER CONFIDENCE IN A GENERAL MODEL
BLEND FOR THIS WAVE.
---PRIOR DISCUSSION---
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/ECMWF BLEND
CONFIDENCE: SLIGHTLY ABOVE AVERAGE
19Z UPDATE: THE 12Z UKMET AND CMC CONTINUE TO BE QUITE AMPLIFIED
FAVORING THE NORTHERN PORTION OF THE SURFACE INVERTED TROF/WAVE
WITH SLIGHTLY STRONGER DEEPER MID-LEVEL CORE TO THE SYSTEM. THE
12Z ECMWF TRENDED THIS DIRECTION AS WELL AND LIES BETWEEN THE NAM
AND CMC/UKMET SOLUTIONS, FURTHER SUPPORTING LESS INFLUENCE OF THE
WEAKER GFS. STILL WILL FAVOR A NAM/ECMWF SOLUTION BUT SOME VERY
LOW PERCENTAGE OF UKMET/CMC MAY BE INCORPORATED TO HANDLE THIS
REDUCED SPREAD IN SOLUTIONS.
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
19Z UPDATE: AFTER 48HRS, THE 12Z GEFS SOLUTION BROADENS GIVEN
GREATER NUMBER OF SOLUTIONS SLOWING (EVEN SLOWER THAN THE 12Z GFS
ITSELF). LIKEWISE, THE UKMET (WHICH IS ON PACE WITH THE 15Z NHC
TRACK BUT NORTH) AND ECMWF SLOW RELATIVE TO THEIR 00Z SOLUTIONS
WITH THE ECMWF LAGGING THE GFS, STILL. WHILE THE 12Z CMC DID
SPEED UP RELATIVE TO THE 00Z SOLUTION, IT REMAINS THE SLOWEST
SOLUTION WITH CONTINUED SUGGESTION THAT THE DOWNSTREAM RIDGE IS
STRONGER AND POTENTIAL FOR THE SYSTEM TO STALL. SO THERE REMAINS
SLIGHTLY BELOW AVERAGE CONFIDENCE ESPECIALLY AFTER 60HRS AND THE
06Z GFS/GEFS AND 00Z ECENS MEAN MATCH THE 15Z FORECAST TRACK THE
BEST.
---PRIOR DISCUSSION---
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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