674
FXUS10 KWNH 181832
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
231 PM EDT MON MAY 18 2020
VALID MAY 18/1200 UTC THRU MAY 22/0000 UTC
...SEE NOUS42 KWNO (ADMSDM) FOR THE STATUS OF THE UPPER AIR
INGEST...
12Z MODEL EVALUATION INCLUDING PREFERENCES AND CONFIDENCE
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TROPICAL STORM ARTHUR
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PREFERENCE: NATIONAL HURRICANE CENTER OFFICIAL TRACK
BEST MODEL PROXY: 12Z GFS/ECMWF BLEND
CONFIDENCE: SLIGHTLY ABOVE AVERAGE
TROPICAL STORM ARTHUR AS OF 15Z IS MOVING NORTH-NORTHEAST AND
STARTING TO PULL AWAY FROM THE NC OUTER BANKS. OVER THE NEXT 24 TO
36 HOURS, THE SYSTEM IS FORECAST TO GRADUALLY TURN OFF TO THE EAST
AND AWAY FROM THE EAST COAST. THE 12Z NAM AND EVEN MORE SO THE 12Z
CMC ARE ON THE SLOWER SIDE OF THE GUIDANCE SPREAD. THE CMC IS ALSO
A WEAK OUTLIER WITH THE SYSTEM. MEANWHILE, THE 12Z UKMET IS THE
FASTEST OF ALL THE DETERMINISTIC MODELS. THE BETTER MODEL
CLUSTERING AND CONSENSUS FAVORS THE 12Z GFS AND 12Z ECMWF WHICH AS
A BLEND IS THE BEST PROXY TO THE LATEST NHC TRACK. PLEASE CONSULT
THE LATEST NHC FORECAST ADVISORIES FOR MORE INFORMATION ON ARTHUR.
CONSOLIDATION OF MIDWEST/GULF COAST TROUGHS INTO CUT-OFF UPPER LOW
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND...THROUGH 60 HOURS
12Z GEFS/ECMWF AND 00Z ECENS MEAN BLEND..AFTER 60 HOURS
CONFIDENCE: SLIGHTLY ABOVE AVERAGE
A PAIR OF UPPER TROUGHS AND ASSOCIATED CLOSED LOWS OVER THE
CENTRAL U.S., ONE OVER ILLINOIS AND THE OTHER ENTERING ALABAMA,
WILL CONSOLIDATE OVER THE NEXT DAY INTO A LARGE CUT-OFF LOW THAT
SETTLES OVER THE TENNESSEE VALLEY TUESDAY AND WEDNESDAY BEFORE
THEN GRADUALLY WEAKENING AND LIFTING NORTHWARD BACK INTO THE OHIO
VALLEY BY THURSDAY. MODEL SPREAD IS MINIMAL THROUGH WEDNESDAY (60
HOURS), BUT BY THURSDAY, THE 12Z NAM AND 12Z GFS ARE FASTER TO
LIFT THE ENERGY BACK NORTH INTO THE OHIO VALLEY VERSUS THE
NON-NCEP MODELS. OF THE NON-NCEP MODELS, THE 12Z CMC IS THE
FARTHEST SOUTHEAST SOLUTION AND ACTUALLY TRENDED FARTHER SOUTHEAST
COMPARED TO ITS PREVIOUS RUN, AND IN EFFECT THIS MAKE IT AN
OUTLIER SOLUTION. REGARDING DEPTH, THE NAM IS A TAD STRONGER THAN
ALL OF THE GLOBAL MODELS AT THE END OF THE PERIOD. THE LATEST GEFS
MEAN AND ECENS MEAN ARE BOTH A TAD SPLIT BY THE END OF THE PERIOD
TOO WITH THE CLOSED LOW PLACEMENT, WITH THE GEFS MEAN FARTHER
NORTH AND THE ECENS MEAN FARTHER SOUTH, HOWEVER THE 12Z GEFS MEAN
TRENDED A BIT FARTHER SOUTH AND IS A BIT SOUTH OF THE NAM AND GFS
SOLUTIONS. THIS TREND CLUSTERS IT EVEN BETTER WITH THE 12Z ECMWF
AND 00Z ECENS MEAN. THEREFORE, WILL RECOMMEND A GENERAL MODEL
BLEND THROUGH 60 HOURS, WITH A BLEND OF THE 12Z GEFS/ECMWF AND 00Z
ECENS MEAN THEREAFTER.
DEEP UPPER TROUGH ADVANCING ACROSS THE WESTERN U.S. BY TUESDAY
SECONDARY UPPER TROUGH OVER THE PACIFIC NORTHWEST BY THURSDAY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND...THROUGH 60 HOURS
12Z GFS/ECMWF BLEND...AFTER 60 HOURS
CONFIDENCE: SLIGHTLY ABOVE AVERAGE
WITH THE AMPLIFYING UPPER-LEVEL PATTERN ACROSS THE CONTINENTAL
U.S., A LARGE UPPER-LEVEL TROUGH AND ASSOCIATED CLOSED LOW IS
FORECAST TO CROSS THE WEST COAST TODAY AND ADVANCE INLAND ACROSS
THE INTERMOUNTAIN WEST BY TUESDAY. GIVEN THE LARGER SCALE OMEGA
BLOCK PATTERN EVOLVING ACROSS THE U.S., THIS UPPER LOW/TROUGH
ACROSS THE WEST WILL SLOW DOWN AND SHOULD REMAIN IN PLACE GOING
THROUGH WEDNESDAY. HOWEVER, THE ARRIVAL OF ANOTHER STRONG UPPER
TROUGH AND ASSOCIATED CLOSED LOW FROM THE GULF OF ALASKA AND
CROSSING THE PACIFIC NORTHWEST BY THURSDAY SHOULD ACT TO KICK OUT
THE ENERGY OVER THE INTERMOUNTAIN WEST AND LARGELY BACK INTO
SOUTHWEST CANADA, ALTHOUGH THERE WILL BE A TRAILING TROUGH AXIS
THAT ADVANCES EAST ACROSS THE ROCKIES AND THE NORTHERN HIGH PLAINS
BY THE END OF THE PERIOD. MODEL SPREAD IS FAIRLY MODEST THROUGH
MOST OF THE PERIOD WITH THE MASS FIELD EVOLUTION ACROSS THE WEST.
HOWEVER, THE 12Z NAM, 12Z GFS AND 12Z UKMET ARE PERHAPS A LITTLE
FASTER TO LIFT THE INITIAL ENERGY NORTHWARD OUT OF THE
INTERMOUNTAIN WEST AND ACROSS THE NORTHERN ROCKIES VERSUS THE 12Z
CMC, AND 12Z ECMWF. BY THE END OF THE PERIOD, THE NAM IS SEEN AS
BEING A WEAK OUTLIER WITH THE SURFACE LOW CENTER OVER SOUTHWEST
CANADA. WILL PREFER A GENERAL MODEL BLEND THROUGH 60 HOURS, WITH A
BLEND OF THE GFS AND ECMWF THEREAFTER GIVEN OVERALL BETTER MODEL
CLUSTERING AND ENSEMBLE SUPPORT WITH BOTH UPPER TROUGHS IMPACTING
THE WEST THIS PERIOD.
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML
ORRISON
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