696
FXUS10 KWNH 271813
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
212 PM EDT SAT JUN 27 2020
VALID JUN 27/1200 UTC THRU JUL 1/0000 UTC
...SEE NOUS42 KWNO (ADMSDM) FOR THE STATUS OF THE UPPER AIR
INGEST...
12Z MODEL EVALUATION INCLUDING PREFERENCES AND FORECAST CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
18Z UPDATE: THE 12Z CMC TRENDED EASTWARD WITH THE TROUGH AXIS
ACROSS THE WESTERN U.S. AND THE UPPER HIGH OVER THE GREAT LAKES
AND ONTARIO BY THE END OF THE FORECAST PERIOD, AND CLOSER TO THE
OTHER GUIDANCE COMPARED TO ITS 00Z RUN. IT IS THE MOST AMPLIFIED
WITH THE DEGREE OF AMPLIFICATION OF THE UPPER TROUGH ACROSS THE
INTERMOUNTAIN WEST, AND INLINE WITH THE MODEL CONSENSUS ACROSS THE
EAST. THE 12Z UKMET ALSO TRENDED STRONGER ACROSS THE WESTERN U.S.
FOR THE DAY 3 PERIOD. THE 12Z ECMWF REMAINS STRONGER WITH THE
SECOND SHORTWAVE CROSSING THE CENTRAL AND NORTHERN PLAINS COMPARED
TO THE OTHER GUIDANCE.
CLOSED LOW OVER QUEBEC AND ACCOMPANYING SHORTWAVES
TROUGH IMPACTING THE NORTHEAST
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-NAM BLEND
CONFIDENCE: SLIGHTLY ABOVE AVERAGE
AN UPPER LEVEL LOW INITIALLY OVER QUEBEC WILL SUSTAIN A BROAD
UPPER LEVEL TROUGH CENTERED OVER THE EAST COAST THROUGH THE
WEEKEND. THE MODELS ARE IN DECENT AGREEMENT ON THE STRUCTURE OF
THIS LOW OVER QUEBEC AND THE SOUTHWARD EXTENSION OF THE TROUGH
ACROSS THE NORTHEAST U.S. THIS WEEKEND. ON SUNDAY, A REINFORCING
SHORTWAVE TROUGH WILL CROSS THE GREAT LAKES AND HELP TO AMPLIFY
THE SYNOPTIC SCALE TROUGH OVER THE NORTHEAST, AND THE MODELS
SUPPORT THE CLOSED DROPPING SOUTH ACROSS NEW ENGLAND FOR THE
BEGINNING OF THE WEEK. THE MAIN DIFFERENCE NOTED IN THE MODELS IS
A SOUTHWARD DISPLACEMENT WITH THE 12Z NAM BY TUESDAY REGARDING THE
UPPER LOW PLACEMENT, AND SIMILAR TO EARLIER NAM FORECAST RUNS, SO
A NON-NAM BLEND WILL BE PREFERRED FOR THIS REGION.
DEEP UPPER TROUGH/CLOSED LOW ACROSS THE ROCKIES AND INTERMOUNTAIN
WEST
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF THE 12Z GFS/UKMET/ECMWF
CONFIDENCE: SLIGHTLY ABOVE AVERAGE
A DEEP UPPER TROUGH AND ASSOCIATED CLOSED LOW IS FORECAST TO
AMPLIFY ACROSS THE NORTHERN ROCKIES AND INTERMOUNTAIN WEST THIS
WEEKEND AS AN UPPER-LEVEL RIDGE BUILDS ACROSS THE GULF OF ALASKA
AND ALSO ACROSS THE MIDWEST AND GREAT LAKES REGION, SUGGESTING A
POTENTIAL OMEGA-BLOCK PATTERN. THE MODELS REMAIN IN GOOD
AGREEMENT ON THE EVOLUTION THROUGH SUNDAY EVENING, AFTER WHICH THE
00Z CMC IS DISPLACED TO THE SOUTHWEST WITH THE TROUGH AXIS AND
ALSO WITH THE DOWNSTREAM RIDGE ACROSS THE CENTRAL/NORTHERN PLAINS.
ALTHOUGH THE GFS TRENDED A LITTLE SLOWER IN LIFTING THE TROUGH
TOWARDS THE NORTHEAST BY THE END OF THE FORECAST PERIOD COMPARED
TO ITS 6Z AND 00Z RUNS, IT STILL REMAINS A BIT MORE PROGRESSIVE
THAN THE MODEL CONSENSUS FOR THE DAY 3 PERIOD. TAKING THESE
FACTORS INTO ACCOUNT, A ECMWF/UKMET/NAM BLEND SHOULD SERVE WELL AS
A STARTING POINT IN THE FORECAST PROCESS.
SHORTWAVES LIFTING NORTHEAST OVER THE PLAINS/MIDWEST
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF THE 12Z UKMET/GEFS MEAN/00Z ECENS MEAN
CONFIDENCE: AVERAGE
AHEAD OF THE DEEP WESTERN U.S. TROUGH/CLOSED LOW WILL BE A PAIR OF
SHORTWAVE TROUGHS THAT EJECT NORTHEAST OUT OF THE SOUTHWEST AND
ACROSS THE PLAINS AND MIDWEST. SIMILAR TO EARLIER RUNS, THE 12Z
NAM CONTINUES TO SUGGEST A STRONGER SOLUTION WITH THE FIRST
SHORTWAVE AS IT TRACKS TOWARDS THE NORTHEAST FROM THE CENTRAL
PLAINS TO THE UPPER MIDWEST THROUGH SUNDAY, IN CONTRAST TO THE
GLOBAL MODELS BEING LESS AMPLIFIED. THE SECOND SHORTWAVE HAS SOME
MODEL SPREAD NOTED AS THE 00Z ECMWF/ECENS MEAN SUPPORT A SOMEWHAT
STRONGER SOLUTION VERSUS THE REMAINING GUIDANCE, WHICH IS A LITTLE
LESS AMPLIFIED. FOR NOW, A BLEND OF THE ENSEMBLE MEANS AND THE
12Z UKMET WILL BE PREFERRED WITH BOTH SHORTWAVE IMPULSES.
REMNANT ENERGY ACROSS THE LOWER MS VALLEY
WEAKNESS LINGERING OVER TEXAS
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: ABOVE AVERAGE
THE MODEL SUPPORT A GRADUAL BUILDING OF THE SUBTROPICAL RIDGE THIS
WEEKEND ACROSS THE FL PENINSULA AND ADJACENT AREAS OF THE GULF
COAST STATES. SOME OF THE WEAK SHORTWAVE ENERGY LINGERING OVER
THE LOWER MISSISSIPPI VALLEY SHOULD SHEAR OUT OVER TOP OF THE
RIDGE THROUGH SATURDAY. HOWEVER, THERE WILL STILL BE A BROAD
MID-LEVEL WEAKNESS/TROUGH LINGERING OVER TEXAS WHICH SHOULD TEND
TO RETROGRADE WESTWARD THROUGH SATURDAY, BEFORE THEN LIFTING NORTH
ACROSS THE SOUTHERN AND CENTRAL PLAINS AHEAD OF THE DEEP WESTERN
U.S. TROUGH/CLOSED LOW. A GENERAL MODEL BLEND WILL AGAIN BE
PREFERRED WITH THE WEAK TROUGH OVER TEXAS.
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML
HAMRICK
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