699
FXUS10 KWNH 091841
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
240 PM EDT SUN AUG 09 2020
VALID AUG 09/1200 UTC THRU AUG 13/0000 UTC
...SEE NOUS42 KWNO (ADMSDM) FOR THE STATUS OF THE UPPER AIR
INGEST...
12Z MODEL EVALUATION INCLUDING FINAL PREFERENCES AND FORECAST
CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
..LONGWAVE TROUGHING OVER THE NORTHWEST TUESDAY-WEDNESDAY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON 12Z GFS BLEND
CONFIDENCE: AVERAGE
AS A BROAD MID-UPPER LEVEL TROUGH AXIS TRANSLATES EASTWARD FROM
THE NORTHEASTERN PACIFIC EARLY THIS WEEK, REACHING SOUTHWESTERN
CANADA AND THE NORTHWESTERN U.S. TUESDAY INTO WEDNESDAY. OF THE
LATEST GUIDANCE, ONLY THE 12Z GFS STANDS OUT WITH A SLOWER
PROGRESSION OF A SHORTWAVE INTO WASHINGTON AND OREGON LATE
WEDNESDAY. FOR NOW, PREFER TO GO TOWARD THE STRONGER CONSENSUS,
OUTSIDE OF THE 12Z GFS.
...WEAK TROUGHING/SURFACE LOW ALONG THE SOUTHEASTERN U.S. COAST ON
WEDNESDAY.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z GFS, 12Z ECMWF, 12Z UKMET BLEND
CONFIDENCE: BELOW AVERAGE
MODEL FORECASTS TAKE AN EXISTING MCV OVER THE LOWER OHIO VALLEY
FROM SUNDAY MORNING, SOUTHEASTWARD TOWARD THE CAROLINAS BY
WEDNESDAY MORNING. THE MODELS DIFFER IN STRENGTH REGARDING THIS
FEATURE WITH MOST DEVELOPING A SURFACE LOW INTO THE SOUTHEAST AND
NEAR THE COASTLINE. THE ENSEMBLES DEPICT THIS FEATURE RATHER WELL,
AND WHILE SINGLE MODEL IS AN OUTLIER, THE 12Z NAM IS STRONGEST AND
12Z CMC LIES ON THE EASTERN EDGE OF THE LATEST SPREAD WHILE ALSO
LEANING TOWARD THE STRONGER SIDE OF THE GUIDANCE. THE 12Z GFS IS
WEAKEST BUT A BLEND OF THE GFS WITH THE 12Z ECMWF AND 12Z UKMET
APPEARS TO BE THE BEST COMPROMISE FOR THIS SYSTEM. CONFIDENCE IS
LOW GIVEN THE ROLE OF FUTURE CONVECTION IN THE EVOLUTION OF THIS
FEATURE.
...REMAINDER OF OVERALL WEATHER PATTERN ACROSS THE CONTINENTAL U.S.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND LED BY THE 12Z GFS AND 12Z ECMWF
CONFIDENCE: AVERAGE
THE REMAINDER OF THE U.S. WILL FEATURE QUASI-ZONAL FLOW ACROSS THE
NORTHERN HALF OF THE NATION WITH A BI-MODAL RIDGE CENTERED OVER
THE LOWER MISSISSIPPI VALLEY AND SOUTHERN ARIZONA/NEW MEXICO. A
LARGE CLOSED LOW WILL TRACK EAST ACROSS CANADA WITH SOME WEAKENING
THROUGH WEDNESDAY. A COLD FRONT WILL FOLLOW AT THE SURFACE WITH
POTENTIAL FOR CONVECTIVE FLARE UPS NEAR THE FRONTAL BOUNDARY.
WHILE DIFFERENCES EXIST WITH THE MODELS REGARDING THESE FLARE UPS
AND THEIR IMPACTS ON THE MID-LEVELS, NO SINGLE MODEL CAN BE RULED
OUT WITH ANY CONFIDENCE. AT THIS TIME, A GENERAL MODEL BLEND IS
PREFERRED BUT WITH THE MOST WEIGHT TOWARD THE 12Z GFS AND `1Z
ECMWF AS THEY ARE CLOSER TO THE MIDDLE OF THE MODEL SPREAD WITH
FEATURES ACROSS THE REMAINDER OF THE U.S., NOT ALREADY DISCUSSED
IN THE ABOVE SECTIONS.
THERE WERE NO SIGNIFICANT DIFFERENCES NOTED WITH THE 12Z
ECMWF/UKMET/CMC COMPARED TO THEIR PREVIOUS 00Z CYCLES.
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML
THIS PRODUCT WILL TERMINATE AUGUST 15, 2020:
WWW.WEATHER.GOV/MEDIA/NOTIFICATION/PDF2/SCN20-58PMDHMD_TERMINATION.
OTTO
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