921
FXUS10 KWNH 190427
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1226 AM EDT TUE MAY 19 2020
VALID MAY 19/0000 UTC THRU MAY 22/1200 UTC
...SEE NOUS42 KWNO (ADMSDM) FOR THE STATUS OF THE UPPER AIR
INGEST...
00Z 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: 00Z GFS, 12Z ECMWF BLEND
CONFIDENCE: SLIGHTLY ABOVE AVERAGE
T.S. ARTHUR CONTINUES TO PULL AWAY FROM THE EAST COAST WITH ITS
NORTH-NORTHEAST MOTION. OVER THE NEXT 24 HOURS, THE SYSTEM WILL
GRADUALLY TURN TO THE EAST. THE LATEST GUIDANCE STILL EXHIBITS
SOME DIFFERENCES, WITH THE 12Z CMC CONSIDERABLY SLOW WHILE THE 12Z
UKMET IS ON THE FASTER SIDE OF THE MODEL SPREAD. THE NAM/GFS DO
TREND SLOWER THAN THE ECMWF BEYOND 24 HOURS BUT THE BEST MODEL
BLEND PROXY TO THE OFFICIAL NHC TRACK IS A COMPROMISE BLEND OF THE
GFS/ECMWF. PLEASE CONSULT THE LATEST NHC FORECAST ADVISORIES FOR
MORE INFORMATION ON ARTHUR.
CUT-OFF LOW OVER LOWER OHIO AND TN RIVER VALLEYS
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND...THROUGH 60 HOURS
ECMWF/UKMET/GEFS BLEND THEREAFTER
CONFIDENCE: SLIGHTLY ABOVE AVERAGE
LARGE ANOMALOUS CLOSED UPPER LEVEL WILL FURTHER REMOVE ITSELF FROM
THE NORTHERN STREAM FLOW AND BECOME CUT-OFF IN THE NEXT 12-24
HOURS OVER THE LOWER OHIO VALLEY, EVENTUALLY SETTLING OVER THE TN
RIVER VALLEY BY DAY 2/3. THROUGH 60 HOURS, THE MODEL AGREEMENT IS
QUITE HIGH AND THE LATEST GUIDANCE SHOWS VERY GOOD PREDICTABILITY
AND CONSISTENCY FROM THE PAST SEVERAL RUNS. BEYOND 60 HOURS, THE
CMC BECOMES AN OUTLIER AND UNUSABLE AS IT DRIFTS THE LOW TOO FAR
TO THE EAST AND TOO FAST. THE 00Z GFS SHOWS AN WEAKENING/OPENING
UP WAVE EARLIER THAN THE REST OF THE MODELS AND ALLOW THE FEATURE
TO LIFT NORTH TOWARD THE GREAT LAKES BY THE END OF THE PERIOD,
WHICH APPEARS TO BE TOO FAST LOOKING AT THE ENSEMBLE. THE
ECMWF/UKMET SHOW BETTER RUN TO RUN CONSISTENCY AND ARE BETTER
ALIGNED WITH THE ENSEMBLE MEANS (INCLUDING THE GEFS) SUCH THAT
WILL BE THE RECOMMENDED MODEL BLEND PREFERENCE AT THIS TIME.
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
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. THROUGH 60 HOURS, THE MODEL GUIDANCE
SHOWS PRETTY GOOD PREDICTABILITY BUT BEYOND THAT, WITH THE
APPROACH OF THE STRONGER SECONDARY SYSTEM, HOW QUICKLY THIS ENERGY
EJECTS EASTWARD IS DIFFERENT IN THE VARIOUS DETERMINISTIC
SOLUTIONS. THE NAM AND CMC APPEAR TO BE TOO FAST AND TOO DEEP, SO
FOR NOW, WILL PREFER A ECMWF/GFS BLEND AFTER 60 HOURS WHICH ALIGNS
BETTER WITH THE ENSEMBLE MEANS.
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML
TAYLOR
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