Prognostic Meteorological Discussion
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FXUS10 KWNH 020452
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1251 AM EDT WED SEP 02 2015

VALID SEP 02/0000 UTC THRU SEP 05/1200 UTC

...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR
INGEST...

00Z NAM/GFS EVALUATION AND PRELIMINARY PREFERENCES

UPPER TROUGH FORMING ACROSS THE PACIFIC NORTHWEST...

PREFERENCE: MODEL CONSENSUS
CONFIDENCE: AVERAGE

THE MAIN DIFFERENCES INVOLVE STRENGTH.  THE GFS IS STRONGER WITH
THE CLOSED LOW CENTER OVER NORTHERN CALIFORNIA BY 12Z SAT...WITH
THE NAM/12Z ECMWF SLIGHTLY WEAKER.  A CONSIDERABLE NUMBER OF
GFS/ENSEMBLE MEMBERS INCLUDING THE PARALLEL GEFS PROVIDE
SUFFICIENT SUPPORT OF THE STRONGER GFS TO BE WORTHY OF INCLUSION
WITH THE WEAKER SCENARIO.  THUS...RECOMMEND A SOLUTION NEAR THE
CONSENSUS AT THIS TIME.

SHORTWAVE TROUGH ACROSS THE UPPER MIDWEST...

PREFERENCE: BEFORE 12Z THU...EQUAL BLEND GFS/12Z ECMWF
             AFTER 12Z THU...SWITCH TO GFS
CONFIDENCE: BEFORE 12Z THU...AVERAGE
             AFTER 12Z THU...BELOW AVERAGE

MODEL INITIALIZATION AND SHORT TERM TRENDS FAVOR A CONSENSUS
APPROACH TO BEGIN THE PERIOD...WITH THE HI-RES SOLUTIONS LOSING
THEIR DEFINITION BY TONIGHT AND SHIFTING CONVECTION MORE NORTH AND
ALONG THE STATIONARY BOUNDARY.  WHILE CERTAINLY POSSIBLE...THESE
HIGHER RES SOLUTION MAY BE LACKING A SUFFICIENT TRIGGER TO
OVERCOMING THE CAPPING INVERSION.  MEANWHILE...ALL GLOBAL GUIDANCE
IS MUCH FARTHER BY TONIGHT AND THURSDAY...PERHAPS DUE TO THEIR
CONVECTIVE PARAMETERIZATIONS THAT ALLOW FOR EASIER TRIGGERING.
GIVEN THAT GROWTH OF THE SHORTWAVE TROUGH IS ALREADY OCCURRING DUE
TO CONVECTION AND THAT TRAINING/BACKBUILDING MAY SUSTAIN
DEVELOPMENT FARTHER SOUTH...THE CURRENT PREFERENCE IS FOR THE MORE
SOUTHWARD GLOBAL GUIDANCE.  THAT SAID THOUGH...THE 12Z ECMWF DOES
MOVE TOWARD THE OUTER EDGES OF THE GUIDANCE BY THU-FRI...BY
STALLING AND EVENTUALLY RETROGRADING THE TROUGH...WITH THE GFS
CLOSER TO THE CONSENSUS AND THUS MORE PROBABLE AFTER THU.

SHORTWAVE TROUGH MOVING FROM THE SOUTHWEST TO THE PLAINS THU-FRI...

PREFERENCE:  NAM AND GFS
CONFIDENCE:  ABOVE AVERAGE

THE NAM AND GFS HAVE TRENDED WESTWARD WITH ITS TRACK AND SHOW GOOD
AGREEMENT WITH EACH OTHER THROUGH 84 HRS...WITH THE 12Z ECMWF MORE
EASTWARD AND PERHAPS OBSOLETE DUE TO AN OLDER RUN.

...MODEL TREND GRAPHICS AT
www.wpc.ncep.noaa.gov/html/model2.shtml...

...500 MB FORECASTS AT
www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml...



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