Prognostic Meteorological Discussion
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000
FXUS10 KWNH 291632
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1232 PM EDT SAT AUG 29 2015

VALID AUG 29/1200 UTC THRU SEP 02/0000 UTC

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

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


...SHORTWAVE MOVING SHEARING ACROSS THE GREAT LAKES...

PREFERENCE: GENERAL MODEL COMPROMISE
CONFIDENCE: ABOVE AVERAGE

THE SHORTWAVE TROUGH MOVING OUT OF THE MIDWEST WILL CROSS THE
GREAT LAKES AND PORTIONS OF NORTHERN NEW ENGLAND THROUGH SUN.
DIFFERENCES IN THE GUIDANCE ARE MINIMAL WITH THIS SYSTEM...AND SO
A GENERAL MODEL COMPROMISE WILL BE PREFERRED.


...UPPER TROUGH/CLOSED LOW OVER THE GULF OF MEXICO...

PREFERENCE: BLEND OF THE 12Z GFS AND 00Z ECMWF
CONFIDENCE: AVERAGE

THE MODELS AGREE THAT AN ELONGATED AXIS OF VORTICITY CENTERS WILL
MEANDER ABOUT THE SOUTHERN U.S. THROUGHOUT MUCH OF THE PERIOD. THE
EASTERN BATCH OF SHORTWAVE ENERGY WHICH IS CURRENTLY OVER THE GULF
OF MEXICO WILL LIFT NORTHEAST AND APPROACH THE SOUTHERN
MID-ATLANTIC BY EARLY MONDAY. THE 12Z NAM SPURIOUSLY DEVELOPS SOME
ADDITIONAL VORT ENERGY OVER THE MID-ATLANTIC REGION WHICH NONE OF
THE OTHER MODELS HAVE. MEANWHILE...THE 00Z CMC MERGES THIS ENERGY
WITH THE REMNANTS OF FORMER T.S. ERIKA AND ALLOWS FOR STRONGER
HEIGHT FALLS TO EVOLVE OVER THE SOUTHEAST. THE STRONGER MODEL
CLUSTERING WOULD SUGGEST A BLEND OF THE 12Z GFS AND 00Z ECMWF.
FARTHER WEST...ANOTHER MID LEVEL WEAKNESS IS FORECAST TO SLOWLY
RETROGRADE TOWARD THE LOWER MS VALLEY/OZARKS REGION...AND WITH THE
12Z GFS AND 00Z ECMWF REASONABLY WELL CLUSTERED AND SUPPORTED BY
THE ENSEMBLE MEANS...A BLEND OF THE GFS AND ECMWF WILL BE
PREFERRED.


...MEAN UPPER TROUGH ANCHORING THE WESTERN STATES THROUGHOUT THE
PERIOD...

PREFERENCE: 12Z GFS
CONFIDENCE: AVERAGE

A RATHER POTENT BLOCK ACROSS THE OPEN PACIFIC HAS CONTINUED TO
FORCE A DEEP UPPER TROUGH ACROSS THE EASTERN PACIFIC/WESTERN U.S.
INITIALLY A PAIR OF SYSTEMS WILL INHABIT THE EASTERN/NORTHEASTERN
PACIFIC WITH THE LEAD SYSTEM MOVING INTO THE PACIFIC NORTHWEST
THROUGHOUT TODAY. THESE HEIGHT FALLS SHOULD QUICKLY LIFT
NORTHEASTWARD INTO WESTERN CANADA WHILE THE REMAINDER OF THE UPPER
TROUGH DESCENDS ON THE NORTHWESTERN STATES. A SECOND SHORTWAVE
IMPULSE WILL TRAVERSE THE NORTHERN ROCKIES SUN NIGHT AND CROSS THE
NORTHERN HIGH PLAINS AND SOUTHERN CANADA ON MON. THIS WILL DRIVE A
COLD FRONT AND AN AREA OF LOW PRESSURE EAST ACROSS THE REGION. THE
00Z ECMWF APPEARS TO BE TOO SLOW WITH THE FRONTAL
PROGRESSION...WITH THE 12Z NAM/12Z GFS/00Z UKMET AND 00Z CMC ALL A
BIT FASTER. THE 12Z GFS HAS GOOD AGREEMENT IN GENERAL FROM THE
OTHER GLOBAL MODELS AND IS SUPPORTED BY THE 06Z GEFS MEAN. WILL
PREFER A SOLUTION TOWARD THE 12Z GFS


...REMNANTS OF ERIKA...

PREFERENCE: BLEND OF THE 12Z GFS AND 00Z ECMWF
CONFIDENCE: AVERAGE

THE 12Z GFS AND 00Z ECMWF TAKE THE REMNANTS OF FORMER T.S. ERIKA
OFF TO THE WEST-NORTHWEST AND INTO THE EASTERN GULF OF MEXICO ON
SUN. BOTH OF THESE MODELS MAINTAIN THE SYSTEM AS A TROUGH OF LOW
PRESSURE. THE 12Z NAM FOLLOWS A SIMILAR TRACK BUT DOES SHOW A
LITTLE BIT OF DEVELOPMENT OVER THE EASTERN GULF OF MEXICO ON MON
AND ALSO IS FASTER TO TRACK THE SYSTEM NORTH TOWARD THE FL
PANHANDLE. THE 00Z UKMET INSISTS ON A STRONGER SOLUTION WITH
INTENSIFICATION OVER THE EASTERN GULF OF MEXICO AND A TRACK INTO
THE FL PANHANDLE MON NIGHT. THE 00Z CMC SHOWS REGENERATION BY LATE
SUN OVER THE SOUTHEAST GULF OF MEXICO AND A TRACK INTO CENTRAL FL
SUN NIGHT. GIVEN THE CURRENT STATE OF DISORGANIZATION...WILL
PREFER THE WEAKER CONSENSUS MADE UP BY THE GFS AND ECMWF SOLUTIONS.


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

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

ORRISON

$$





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