Prognostic Meteorological Discussion
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000
FXUS10 KWNH 261643
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1242 PM EDT TUE AUG 26 2014

VALID AUG 26/1200 UTC THRU AUG 30/0000 UTC

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


12Z MODEL EVALUATION...INCLUDING THE NAM AND GFS

...COLD FRONT CROSSING THE MIDWEST AND NORTHEAST...

PREFERENCE: GFS/00Z ECMWF BLEND
CONFIDENCE: ABOVE AVERAGE

THE NAM AND GFS ARE VERY SIMILAR WITH THE TIMING OF THIS FRONTAL
BOUNDARY AS IT MOVES FROM THE MIDWEST TODAY INTO THE NORTHEAST ON
WEDNESDAY. BY EARLY THURS MORNING AS THE FRONT MOVES OFF THE
NORTHEAST U.S. COAST...THE NAM BECOMES SLIGHTLY SLOWER WITH THE
FRONT...WHEREAS THE GFS TIMING REMAINS VERY CLOSE TO THE 00Z ECMWF.


...UPPER-LEVEL TROUGH/LOW MOVING FROM THE ROCKIES IN THE PLAINS...
...SURFACE COLD FRONT DEVELOPING LATE WED IN THE LEE OF THE
CENTRAL ROCKIES...

PREFERENCE: GFS/00Z ECMWF BLEND
CONFIDENCE: AVERAGE

THE NAM AND GFS ARE SIMILAR IN HOW THEY HANDLE THE UPPER-LEVEL
FEATURE AS IT CROSSES THE ROCKIES. AS THE SYSTEM MOVES FROM THE
ROCKIES INTO THE CENTRAL PLAINS LATE THURS NIGHT/EARLY FRI...THE
NAM BECOMES LESS AMPLIFIED WITH THE UPPER-LEVEL WAVE RELATIVE TO
THE GFS/00Z ECMWF AS WELL AS THE 00Z UKMET. AS A CONSEQUENCE...THE
NAM APPEARS FASTER RELATIVE TO THE GFS/00Z ECMWF WITH THE EASTWARD
PROGRESSION OF THE SURFACE FRONT ONCE IT DEVELOPS IN THE LEE OF
THE ROCKIES LATE WED AND MOVES INTO THE PLAINS EARLY THURS.


...EASTERLY WAVE ADVANCING WEST ALONG THE GULF COAST...

PREFERENCE: GENERAL MODEL COMPROMISE
CONFIDENCE: ABOVE AVERAGE

MODELS SHOW SLIGHT DIFFERENCES IN TIMING/PLACEMENT OF THE
VORTICITY CENTER ASSOCIATED WITH THIS WAVE...BUT OVERALL AGREEMENT
IS RELATIVELY GOOD. WILL THEREFORE RECOMMEND A GENERAL MODEL
COMPROMISE.


...SHORTWAVE TROUGH DIGGING INTO THE NORTHEAST THROUGH THURS AND
FRI...

PREFERENCE: GFS/00Z ECMWF/00Z UKMET BLEND
CONFIDENCE: ABOVE AVERAGE

THE NAM BECOMES MORE AMPLIFIED RELATIVE TO THE GFS AND THE 00Z
MODEL CONSENSUS BY 00Z THURS AND THIS CONTINUES THROUGH
FRIDAY...WITH THE NAM ULTIMATELY BECOMING MUCH SLOWER THAN THE
AFOREMENTIONED CONSENSUS AS THE TROUGH MOVES OFF THE NORTHEASTERN
U.S. COAST EARLY FRIDAY.


...NORTHERN STREAM TROUGH CLIPPING THE NORTHWESTERN U.S./CANADIAN
BORDER BY FRI...

PREFERENCE: GENERAL MODEL COMPROMISE
CONFIDENCE: AVERAGE

MODEL SPREAD WITH RESPECT TO THIS FEATURE IS RELATIVELY
LARGE...PARTICULARLY WITH RESPECT TO TIMING. THE NAM AND GFS ARE
ON THE FASTER SIDE OF THE SPREAD ENVELOPE...WITH THE 00Z
ECMWF/CMC/UKMET ON THE SLOW SIDE. THE 00Z ECMWF WAS A LITTLER
SLOWER THAN ITS ENSEMBLE MEAN...WHICH SUGGESTS THAT A COMPROMISE
BETWEEN THE FASTER NCEP GUIDANCE AND THE SLOWER NON-NCEP GUIDANCE
MAY BE IN ORDER.


...DEEP TROUGH DIGGING JUST OFF THE NORTHWEST BY FRI...

PREFERENCE: GENERAL MODEL COMPROMISE
CONFIDENCE: AVERAGE

WHILE TIMING AND AMPLITUDE DIFFERENCES EXIST WITH THIS FEATURE...A
MIDDLE GROUND SOLUTION DERIVED FROM A GENERAL MODEL COMPROMISE
APPEARS TO BE A SAFE BET AT THIS TIME. THE 00Z ECMWF ENSEMBLE MEAN
ALSO APPEARS TO REPRESENT A GOOD COMPROMISE.


...MODEL TREND GRAPHICS AT
www.wpc.ncep.noaa.gov/html/model2.shtml...
...500 MB FORECASTS AT
www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml...

RYAN
$$




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