687
FXUS10 KWNH 271924
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
324 PM EDT TUE AUG 27 2019
VALID AUG 27/1200 UTC THRU AUG 31/0000 UTC
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR
INGEST...
12Z FINAL MODEL EVALUATION WITH PREFERENCES AND FORECAST CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
..OVERALL PATTERN ACROSS THE CONUS
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
TD 06L NHC PROXY: 12Z UKMET/ECMWF AND 00Z GEFS BLEND
CONFIDENCE: SLIGHTLY ABOVE AVERAGE
19Z UPDATE:
FOR TD6, UKMET REMAINS VERY CLOSE TO ITS PREVIOUS RUN, WHILE THE
ECMWF HAS SLOWED ONCE AGAIN TO BECOME MORE IN LINE WITH THE
PREVIOUS BLEND AND CLOSE TO THE NHC TRACK. FOR THIS REASON HAVE
ADDED THE ECMWF TO THE PREFERRED BLEND FOR THIS UPDATE. ELSEWHERE,
A GENERAL MODEL BLEND STILL REMAINS SUFFICIENT. THE GFS IS A BIT
FAST WITH SWINGING A TROUGH AXIS/SHORTWAVE ACROSS NEW ENGLAND ON
THURSDAY WITH MAY SPREAD QPF A BIT TOO FAST, BUT IS OTHERWISE WELL
WITHIN THE ENSEMBLE ENVELOPE THROUGH THE PERIOD ACROSS THE
REMAINDER OF THE CONUS.
PREVIOUS DISCUSSION:
FOR TD6 MOVING NORTHEAST OFF THE EASTERN COAST OF THE CONUS
THROUGH THE PERIOD, THE NHC TRACK IS A BIT SLOWER THAN THE
MAJORITY OF THE AVAILABLE GLOBAL SUITE. HOWEVER, A BLEND OF THE
UKMET AND GEFS MEAN PRODUCES SOMETHING REASONABLY CLOSE TO THE
TRACK AS THESE ARE ON THE SLOW EDGE OF THE ENVELOPE. THE TREND IN
THE ECMWF HAS BEEN TOWARDS THIS SLOWER SOLUTION OVER THE PAST 3
RUNS, SO SOME WEIGHT ON THE ECMWF IS USABLE, BUT WILL END UP WITH
SOMETHING THAT GRADUALLY GETS MORE AWAY FROM THE OFFICIAL TRACK.
FOR THIS REASON, A UKMET/GEFS BLEND IS SUGGESTED. THIS WILL ALSO
PLAY A ROLE IN THE QPF, ESPECIALLY ACROSS EASTERN NEW ENGLAND
THURSDAY AS INTERACTION WITH THE APPROACHING FRONT HAS THE
POTENTIAL TO PRODUCE HEAVY RAINFALL. THE UKMET IS THE MOST
AGGRESSIVE WITH QPF, AND DESPITE ITS TYPICAL WET BIAS, IT BEING
THE BEST DETERMINISTIC MODEL TOWARDS THE TRACK SUGGESTS AN
INCREASING LIKELIHOOD FOR HEAVY RAINFALL, SO FROM A QPF STANDPOINT
A GENERAL MODEL BLEND IS ACCEPTABLE HERE.
ELSEWHERE ACROSS THE CONUS, THERE IS GENERALLY GOOD AGREEMENT IN A
WESTERN RIDGE/EASTERN TROUGH GENERALLY BECOMING MORE ZONAL BY DAY
3. WHILE SUBTLE DIFFERENCES EXIST IN TIMING AND INTENSITY OF
FEATURES WHICH WILL EVENTUALLY DESCRIBE THE SYNOPTIC SHIFT, THE
SPREAD APPEARS MINIMAL. THE BIGGEST DISCREPANCIES LIE IN THE
AMPLITUDE OF THE WESTERN RIDGE EARLY IN THE FORECAST PERIOD, BUT
OVERALL THE QPF ALONG THE STALLED FRONT IN THE SOUTH AND HEIGHT
ANOMALIES BY DAY 3 FEATURE A SMALL ENVELOPE, SO A GENERAL MODEL
BLEND SHOULD BE SUFFICIENT.
MODEL TRENDS AT WWW.WPC.NOAA.GOV/HTML/MODEL2.HTML
500 MB FORECASTS AT WWW.WPC.NOAA.GOV/H5PREF/H5PREF.SHTML
WEISS
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