630
FXUS10 KWNH 021853
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
252 PM EDT THU JUL 02 2020
VALID JUL 02/1200 UTC THRU JUL 06/0000 UTC
...SEE NOUS42 KWNO (ADMSDM) FOR THE STATUS OF THE UPPER AIR
INGEST...
12Z FINAL MODEL EVALUATION INCLUDING PREFERENCES AND FORECAST
CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
EASTERN U.S. TROUGH
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND, NON UKMET/CMC D3
CONFIDENCE: ABOVE AVERAGE EARLY, AVERAGE D3
19Z UPDATE: BIGGEST CHANGE WITH THE 12Z NON-NCEP SUITE WAS TO
REMOVE THE UKMET WHICH NOW CUTS OFF THE MID-LEVEL TROUGH INTO A
CLOSED LOW OVER THE GULF COAST SUNDAY, WHILE ALSO BEING THE
STRONGEST WITH A SHORTWAVE DIGGING INTO THE CENTRAL PLAINS AT THE
END OF THE FORECAST PERIOD. OTHERWISE, THE PREFERENCES REMAIN
UNCHANGED.
PREVIOUS DISCUSSION:
TWO FEATURES OF INTEREST EMBEDDED IN THE PERSISTENT EASTERN CONUS
TROUGH. THE FIRST IS ACROSS NEW ENGLAND WHERE A WAVE OF LOW
PRESSURE AND BACK DOOR TYPE COLD FRONT WILL SAG SOUTHWARD LATE
FRIDAY INTO SATURDAY. THE GFS IS A BIT FASTER THAN THE REMAINING
CONSENSUS, BUT NOT OUTSIDE THE TYPICAL SPREAD BY D3, SO A GENERAL
MODEL BLEND IS ACCEPTABLE.
ALONG THE GULF COAST, A BROAD TROUGH WILL DEVELOP BENEATH THE
RIDGE EXPANDING FROM THE PLAINS INTO THE MID-ATLANTIC ON FRIDAY.
THIS TROUGH WILL THEN BE AMPLIFIED BY MID-LEVEL IMPULSES ROTATING
ATOP THE RIDGE AND INTO THE GULF COAST. WHILE DISCREPANCIES EXIST
IN THE TIMING, INTENSITY, AND PLACEMENT OF THESE SMALLER SCALE
SHORTWAVES/MCVS, THE END RESULT IS A BROAD AND MODEST TROUGH THAT
GETS STUCK ALONG THE GULF COAST AND TOWARDS THE SOUTHEAST CONUS.
THE CMC CLOSES OFF A LOW ALONG THE CENTRAL GULF COAST BY SUNDAY,
AND WHILE THE POSITION OF THIS FEATURE IS SIMILAR TO THE CENTRAL
TROUGH AXIS FROM THE REMAINING GUIDANCE, IT IS THE ONLY MODEL
INDICATING A TROUGH OF THAT STRENGTH. OTHERWISE, A BLEND OF THE
REMAINING MODELS SHOULD SUFFICE. HOWEVER, IS SHOULD BE NOTED THAT
CONFIDENCE DROPS CONSIDERABLY BY SUNDAY DUE TO INTERACTIONS WITH
THE SMALLER SCALE SHORTWAVES, AND POSSIBLE SURFACE LOW DEVELOPMENT
BENEATH THIS TROUGH.
DEEP UPPER TROUGH/CLOSED LOW ACROSS THE PACIFIC NORTHWEST AND
WESTERN CANADA
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-GFS OR UKMET BLEND
CONFIDENCE: SLIGHTLY ABOVE AVERAGE
19Z UPDATE: THE UKMET HAS TRENDED TOWARDS THE GFS WITH STRONGER
SHORTWAVES AND A MORE AMPLIFIED TROUGH ACROSS THE PACNW, WHEREAS
THE 12Z CMC CAME MORE INTO LINE WITH THE PREVIOUS PREFERENCES. THE
UKMET AND GFS ARE NOW OUTLIERS WITH THEIR AMPLITUDES AND TIMING OF
RELEVANT SHORTWAVES COMPARED TO THE CONSENSUS AND PREFERRED BLEND.
PREVIOUS DISCUSSION:
A LARGE CLOSED LOW PIVOTING ACROSS THE PACNW AND INTO WESTERN
CANADA WILL SPIN NEARLY IN PLACE AS SEVERAL VORT IMPULSES ROTATE
CYCLONICALLY AROUND EACH OTHER TO REINFORCE THE TROUGH. THROUGH
SATURDAY, THE GUIDANCE IS IN VERY GOOD AGREEMENT WITH THE POSITION
AND AMPLITUDE OF THIS FEATURE. HOWEVER, BY LATE D2 INTO D3, THE
GFS BECOMES MORE AMPLIFIED WITH A SUBSEQUENT SHORTWAVE EJECTING
FROM THE BASE OF THE TROUGH AND NORTHEAST TOWARDS ALBERTA, CANADA,
WHILE THE CMC LAGS THIS FEATURE LEAVING A FLATTER OVERALL TROUGH.
THE GEFS IS WELL ALIGNED WITH THE OTHER GUIDANCE
(ECMWF/ECENS/NAM/UKMET) WHICH SUGGESTS THE GFS IS TOO AMPLIFIED.
THE GFS ALSO LEAVES A HIGHER QPF SIGNAL DUE TO ITS STRONGER
IMPULSE, AND FOR THIS REASON IS REMOVED FROM THE PREFERENCE.
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML
WEISS
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