Prognostic Meteorological Discussion
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FXUS10 KWNH 271644
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1243 PM EDT THU AUG 27 2015

VALID AUG 27/1200 UTC THRU AUG 31/0000 UTC

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

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


...SHORTWAVE EXITING THE NORTHEAST U.S./SOUTHEAST CANADA THROUGH
FRI...

PREFERENCE: GENERAL MODEL COMPROMISE
CONFIDENCE: ABOVE AVERAGE

THE MODELS ARE IN VERY GOOD AGREEMENT WITH THIS EXITING
SYSTEM...SO A GENERAL MODEL COMPROMISE WILL BE PREFERRED TO
RESOLVE ANY SMALL SCALE DIFFERENCES.


...ELONGATED UPPER TROUGH OVER THE GULF COAST STATES/GULF OF
MEXICO...

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

THE 12Z NAM AGAIN GRADUALLY BECOMES SOMEWHAT STRONGER THAN THE
GLOBAL MODEL CONSENSUS WITH THE TROUGH OVER THE GULF COAST STATES
AND EXTENDING SOUTH OVER THE CENTRAL AND WESTERN GULF OF MEXICO.
THE 00Z CMC WAS SEEN AS BEING PERHAPS A TAD TOO BROAD WITH THE
UPPER TROUGH BY THE END OF THE PERIOD. MEANWHILE...THE 12Z GFS/00Z
ECMWF AND 00Z UKMET SHOW BETTER AGREEMENT AND GIVEN THEIR STRONGER
CLUSTERING...A BLEND OF THESE SOLUTIONS WILL BE PREFERRED.


...DEEP UPPER TROUGH OVER THE EASTERN PACIFIC...
...HEIGHT FALLS/COLD FRONT CROSS THROUGH THE NORTHWEST...

PREFERENCE: NON-NAM CONSENSUS
CONFIDENCE: ABOVE AVERAGE

A DEEP UPPER TROUGH INITIALLY OFFSHORE THE WEST COAST WILL ADVANCE
EAST AND SHEAR INLAND ACROSS THE PACIFIC NORTHWEST BY SAT IN
RESPONSE TO ADDITIONAL STRONG HEIGHT FALLS/TROUGHING DIGGING SOUTH
THROUGH THE GULF OF AK AND TOWARD WESTERN BRITISH COLUMBIA FRI AND
SAT. THE REMNANTS OF THE INITIAL TROUGH WILL CROSS THE NORTHERN
ROCKIES AND HIGH PLAINS ON SUN...AND WILL ALLOW AN ATTENDANT COLD
FRONT TO EJECT OUT INTO THE NORTHERN PLAINS. IN THE WAKE OF THIS
SYS...A BROADER SCALE TROUGH WILL BE EVOLVING ALONG THE WEST
COAST. THE 12Z NAM IS A TAD STRONGER THAN THE GLOBAL MODELS AS THE
INITIAL ENERGY ARRIVES IN ACROSS THE PACIFIC NORTHWEST...WITH THE
GLOBAL MODELS OTHERWISE WELL CLUSTERED. THERE IS REASONABLY GOOD
MODEL AGREEMENT WITH THE DETAILS OF THE FRONTAL PROGRESSION
THROUGH THE NORTHWEST AND INTO THE NORTHERN PLAINS. ALL OF THE
MODELS ALSO SHOW GOOD AGREEMENT WITH THE OVERALL TROUGH AXIS/DEPTH
BY SUN ALONG THE WEST COAST. A NON-NAM CONSENSUS WILL BE THE
PREFERENCE SINCE IT IS LIKELY A LITTLE TOO SHARP WITH THE INITIAL
HEIGHT FALLS.


...SHORTWAVE CROSSING THE NORTHERN PLAINS/UPPER MIDWEST/GREAT
LAKES...

PREFERENCE: BLEND OF THE 12Z NAM AND 00Z ECENS MEAN
CONFIDENCE: BELOW AVERAGE

THE MODELS ARE IN VERY GOOD AGREEMENT IN EJECTING A SHORTWAVE EAST
ACROSS THE NORTHERN PLAINS AND INTO THE UPPER MIDWEST THROUGH FRI.
THEREAFTER...THE SYSTEM SHOULD ADVANCE INTO THE GREAT LAKES REGION
WHILE SLOWING DOWN. THE 00Z ECMWF AND 00Z UKMET ARE THE STRONGEST
SOLUTIONS WITH THIS FEATURE AND ESPECIALLY AS IT MOVES INTO THE
GREAT LAKES REGION. THE 00Z CMC IS THE WEAKEST SOLUTION FOLLOWED
CLOSELY BY THE 12Z GFS. THE 12Z NAM LEANS TOWARD THE STRONGER
ECMWF/UKMET CAMP. CONFIDENCE IS LIMITED...BUT THERE IS GENERALLY
MORE AGREEMENT ON A RELATIVELY DEEPER SOLUTION VERSUS A WEAKER ONE
AS THE SYSTEM IMPACTS THE UPPER MIDWEST AND GREAT LAKE REGION.
HOWEVER...THE ECMWF AND UKMET BOTH APPEAR TO BE TOO STRONG...WITH
THE GFS AND CMC SOLUTIONS TOO WEAK. THE LATEST ECENS MEAN FAVORS
GENERALLY A SOLUTION CLOSE TO THAT OF THE 12Z NAM WHICH IS A
LITTLE WEAKER THAN THE ECMWF AND UKMET. THE GEFS MEAN FAVORS THE
WEAKER GFS/CMC CAMP. CONFIDENCE IS LIMITED...BUT WILL PREFER A
BLEND OF THE 12Z NAM AND 00Z ECENS MEAN AT THIS POINT FOR MASS
FIELDS.


...TROPICAL STORM ERIKA...

PREFERENCE: SEE THE LATEST NHC FORECAST ADVISORY/DISCUSSION

THE LATEST MODELS INSIST ON TRACKING T.S ERIKA WEST-NORTHWEST
THROUGH THE BAHAMAS SAT AND SUN...WITH THE SYSTEM APPROACHING THE
FL PENINSULA BY LATE SUN. THE 12Z NAM AND 12Z GFS TRACK ERIKA A
BIT SOUTH OF THEIR PREVIOUS RUNS AND ARE LEFT OF THE 15Z NHC
FORECAST TRACK. THEY ARE BOTH ALSO NOTABLY WEAKER VERSUS THE
STRONGER 00Z CMC AND ESPECIALLY THE 00Z UKMET WHICH IS THE
STRONGEST AND SLOWEST THROUGH THIS PERIOD. THE 00Z ECMWF FAVORS
THE WEAKER NAM/GFS CAMP...BUT IS JUST A TAD FASTER IN BRINGING
ERIKA TOWARD FAR SOUTH FL BY LATE SUN.


...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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