Prognostic Meteorological Discussion
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000
FXUS10 KWNH 300459
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1259 AM EDT SAT AUG 30 2014

VALID AUG 30/0000 UTC THRU SEP 02/1200 UTC

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

==================================================
00Z NAM/GFS EVALUATION AND PRELIMINARY PREFERENCES
==================================================
NAM/GFS INITIALIZATION ERRORS DO NOT APPEAR TO
SIGNIFICANTLY AFFECT THEIR LARGE SCALE OUTPUT.
==================================================

....TROUGH SWEEPING ACROSS THE GREAT LAKES AND NORTHEAST...

PREFERENCE: BLEND OF 00Z GFS/12Z ECMWF

A BLEND OF THE GFS/ECMWF MAINTAINS WPC CONTINUITY IN THE FORWARD
SPEED OF THIS SYSTEM. THE 12Z UKMET AND CANADIAN WERE SLIGHTLY
FASTER. THE 00Z NAM FITS WELL WITH THE PREFERRED GFS/ECMWF THROUGH
DAY 2. IT THEN DIFFERS IN HANDLING STREAM INTERACTION NEAR THE NEW
ENGLAND COAST...AND PRODUCES A MORE PRONOUNCED SHORTWAVE RIDGE
EXTENDING NORTHWARD INTO CANADA...RELATIVE TO THE GLOBAL MODEL
CONSENSUS.


...SOUTHERN EXTENSION OF TROUGHING OVER THE EASTERN U.S...

PREFERENCE: BLEND OF 00Z GFS WITH 12Z ECMWF/UKMET

A POSITIVELY TILTED NORTHERN STREAM TROUGH AXIS DRAGGING TOWARD
THE MIDDLE MISSISSIPPI VALLEY WILL PHASE WITH AN EASTERLY WAVE
ROUNDING THE SUB-TROPICAL RIDGE TO YIELD A DEFINABLE SHORTWAVE
TROUGH THAT LIFTS THROUGH THE EASTERN U.S. THIS PERIOD. THE MODELS
SPREAD IS SMALL CONSIDERING THE DIFFICULTIES THAT ARISE IN
FORECASTING PHASING...ALONG WITH THE SLIGHT WARM CORE NATURE OF
THE EASTERLY WAVE. IN KEEPING WITH THE PREVIOUS PREFERENCE...WE
GIVE THE NOD TO THE GFS/ECMWF/UKMET. RUNS OF THE CANADIAN HAVE
TENDED TO BE ON THE FAST SIDE. THE 00Z NAM PRODUCES LOWER HEIGHTS
WITHIN THIS DEVELOPING WAVE AND WITH THE SMALL VORTICITY MAXIMUM
LEFT BEHIND IN SOUTH TEXAS. THIS IS A COMMON TRAIT OF THE NAM AT
THIS LATITUDE...BUT ITS FORECAST TIMING AND EVOLUTION ARE
OTHERWISE CLOSE TO CONSENSUS...SO THE OUTPUT MAY STILL BE USEFUL.


...MEDIUM WAVELENGTH PACIFIC TROUGH REACHING THE MIDWEST BY
TUESDAY MORNING...

PREFERENCE: BLEND OF 12Z ECMWF/UKMET/CANADIAN
PREFERENCE: 00Z GFS GOOD EXCEPT DAY 3 WITH SPURIOUS MT/ND SHORTWAVE

A MODERATELY DEEP BUT PROGRESSIVE PACIFIC TROUGH WILL REACH THE
PLAINS BY MONDAY MORNING...WHILE LARGE SCALE LOW LEVEL
CYCLOGENESIS TAKES PLACE OVER CANADA BY THAT TIME. MODEL SPREAD IS
RELATIVELY LOW GIVEN THE LARGE SCALE OF THIS SYSTEM. THERE IS MORE
VARIABILITY WITH RESPECT TO AN UPSTREAM TROUGH...WHICH INFLUENCES
THE PATTERN OVER THE WESTERN/CENTRAL U.S. GOING INTO DAY 3.
GENERALLY THE GLOBAL MODELS ARE SIMILAR ENOUGH...AND FIT NEAR THE
ENSEMBLE MEANS...TO BE BLENDED AS A GROUP. THE 00Z
GFS...HOWEVER...INTRODUCES A PRONOUNCED SHORTWAVE OVER MT/ND ON
DAY 3...WHICH HAS NOT BEEN PRESENT IN PREVIOUS RUNS...AND AS OF
YET HAS NO SUPPORT. THE NAM HAS TENDED TO ACT AS A DEEP OUTLIER
AFTER DAY 1...AS IT PRODUCES LOW LEVEL CYCLOGENESIS SOUTH OF THE
U.S. BORDER...WHEREAS THE CONSISTENT ENSEMBLE SIGNAL IS FOR THIS
TO OCCUR WELL NORTH IN CANADA.


...NEXT PACIFIC TROUGH REACHING THE NORTHWEST BY TUESDAY MORNING...

PREFERENCE: BLEND OF 12Z ECMWF/CANADIAN

THE GFS HAS BEEN SOMEWHAT INCONSISTENT IN TIMING THIS SYSTEM
COMPARED TO THE CONSENSUS OVER THE PAST FEW CYCLES. THE NAM/GFS
ARE FLATTER THAN THE ECMWF/CANADIAN...BUT THE NAM/GFS ARE
SUPPORTED BY THE 12Z UKMET AND GEFS MEAN. OVERALL...PREFER TO SIDE
WITH THE SIGNAL SEEN IN THE ECMWF...WHERE THE ECMWF ENSEMBLE MEAN
HAS SUNK DOWN OR AMPLIFIED INTO A CONFIGURATION FIRST PREDICTED BY
THE OPERATIONAL MODEL. THIS ALSO PRODUCES WHAT LOOKS LIKE A MORE
REASONABLE SPACING OF MODERATELY PRONOUNCED MEDIUM WAVELENGTH
TROUGHS WITHIN THE BROAD TROUGH BEING CARVED OUT OVER CENTRAL
NORTH AMERICA.

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

BURKE
$$





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