264
FXUS10 KWNH 181618
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1217 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/00Z 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 TENDS TO BE A TAD SLOWER
THAN THE GLOBAL MODEL CONSENSUS IN ADVANCING ARTHUR OUT TO SEA,
WITH THE 00Z UKMET THE FASTEST OF ALL THE DETERMINISTIC MODELS.
THE BETTER MODEL CLUSTERING AND CONSENSUS FAVORS THE 12Z GFS AND
00Z ECMWF WHICH AS A BLEND IS THE BEST PROXY TO THE LATEST NHC
TRACK. THE 00Z CMC FOR ITS PART DOES ALIGN ITSELF WELL TRACK WISE
WITH THE GFS/ECMWF CAMP, BUT IS SEEN AS BEING A WEAK OUTLIER.
PLEASE CONSULT THE LATEST NHC FORECAST ADVISORIES FOR MORE
INFORMATION ON ARTHUR.
CONSOLIDATION OF MIDWEST/GULF COAST TROUGHS INTO CUT-OFF UPPER LOW
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PREFERENCE: GENERAL MODEL BLEND...THROUGH 60 HOURS
06Z GEFS/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 OH VALLEY VERSUS THE NON-NCEP
MODELS. THE NAM IS ALSO A TAD STRONGER THAN ALL OF THE GLOBAL
MODELS BY 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
GEFS MEAN FARTHER NORTH AND THE ECENS MEAN FARTHER SOUTH WITH
THEIR RESPECTIVE CLOSED LOW SOLUTIONS. WILL RECOMMEND A GENERAL
MODEL BLEND THROUGH 60 HOURS, WITH A 06Z GEFS MEAN AND 00Z ECENS
MEAN BLEND 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/00Z UKMET/OOZ 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 GFS AND 12Z NAM ARE PERHAPS A LITTLE FASTER TO
LIFT THE INITIAL ENERGY NORTHWARD OUT OF THE INTERMOUNTAIN WEST
VERSUS THE NON-NCEP SOLUTIONS, AND BY THE END OF THE PERIOD, THE
NAM IS SEEN AS BEING A WEAK OUTLIER WITH THE LOW CENTER OVER
SOUTHWEST CANADA. WILL PREFER A GENERAL MODEL BLEND THROUGH 60
HOURS, WITH A BLEND OF THE 12Z GFS, 00Z UKMET AND 00Z 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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