Prognostic Meteorological Discussion
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FXUS10 KWNH 271620
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1119 AM EST SAT DEC 27 2014

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

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

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

...SHORTWAVE LIFTING THROUGH THE UPPER MIDWEST AND UPPER GREAT
LAKES...

PREFERENCE: GENERAL MODEL COMPROMISE
CONFIDENCE: ABOVE AVERAGE

THERE IS GOOD AGREEMENT AMONG THE MODELS WITH THE EXITING
SHORTWAVE AND ASSOCIATED SURFACE LOW OVER THE UPPER MIDWEST WHICH
IS FORECAST TO PROGRESSIVELY CROSS THE UPPER GREAT LAKES REGION
THROUGH TODAY AND TONIGHT. A GENERAL MODEL COMPROMISE WILL BE
PREFERRED.


...SHORTWAVE ENERGY SHEARING OVER THE FOUR CORNERS/SOUTHERN
PLAINS/SOUTHEAST...

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

SHORTWAVE ENERGY LEFT BEHIND OVER THE FOUR CORNERS REGION BY LATER
TODAY WILL SHEAR EAST OUT ACROSS THE SOUTHERN PLAINS ON SUN AND
INTO THE SOUTHEAST ON MON. A FLAT WAVE OF LOW PRESSURE IS EXPECTED
TO FORM ALONG THE TAIL END OF A FRONT OVER THE LOWER MS VALLEY AND
THEN ADVANCE EAST ACROSS THE INTERIOR SOUTHEAST AND SOUTHERN
MID-ATLANTIC REGION. THE MODELS OVERALL HAVE TRENDED WEAKER WITH
THIS SYS...BUT THE 00Z GEM AND 00Z UKMET ARE RELATIVELY STRONGER
AND SLOWER AS COMPARED TO THE WELL-CLUSTERED 12Z GFS AND 00Z
ECMWF. THE 12Z NAM IS THE FASTEST SOLN. THE LATEST GEFS MEAN AND
ECENS MEAN SUPPORT THE DETERMINISTIC GFS/ECMWF CAMP...AND SO A
BLEND OF THE GFS AND ECMWF WILL BE PREFERRED.


...STRONG SHORTWAVE REACHING THE PACIFIC NORTHWEST BY LATER
TODAY...
...JET ENERGY/DEEP TROUGH EVOLVING OVER THE WESTERN U.S THROUGH
TUESDAY...

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

THE MODELS CONTINUE TO ADVERTISE A STRONG UPPER RIDGE DEVELOPING
OFFSHORE THE WEST COAST AND NEAR PORTIONS OF THE GULF OF AK. THIS
WILL ALLOW A SIGNIFICANT AMOUNT OF SHORTWAVE ENERGY TO DIVE SOUTH
DOWN THE EAST SIDE OF THE RIDGE AND INTO THE WESTERN U.S. THROUGH
THE PERIOD. A LEAD SHORTWAVE WILL DIG SOUTH THROUGH THE PAC
NORTHWEST AND GREAT BASIN LATER TODAY THROUGH SUN BEFORE THEN
SHEARING OUT INTO THE PLAINS. THE 12Z NAM IS A RELATIVELY DEEP
OUTLIER WITH THIS IMPULSE. THE 12Z GFS AND 00Z ECMWF ARE WELL
CLUSTERED WITH THIS FEATURE AND APPEAR REASONABLE AS THEY ARE
GENERALLY SUPPORTED BY THE 00Z GEM AND 00Z UKMET.

IN BEHIND THE FIRST SHORTWAVE...STRONGER SHORTWAVE/JET ENERGY
DIGGING SOUTH WILL CARVE OUT A DEEPER TROUGH AND AN ELONGATED
CLOSED LOW OVER THE GREAT BASIN AND INVOLVING CA. THE 12Z NAM IS
THE MOST ROBUST WITH THE HEIGHT FALLS. THE 00Z GEM IS THE
SLOWEST...WITH THE 00Z UKMET RELATIVELY THE FASTEST AND ALSO
SUGGESTING MORE CONCENTRATED ENERGY OVER CENTRAL CA BY THE END OF
THE PERIOD. THE 12Z GFS AND 00Z ECMWF ARE MORE ELONGATED AND A
LITTLE FARTHER EAST WITH THE CLOSED LOW ORIENTATION. THE LATEST
GEFS MEAN AND ECENS MEAN SUPPORT THIS ORIENTATION...AND SO A BLEND
OF THE GFS AND ECMWF APPEARS REASONABLE FOR THE TIME BEING.


...NORTHERN STREAM SHORTWAVE TROUGH DROPPING ACROSS THE UPPER
MIDWEST BY TUESDAY...

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

THE MODELS INDICATE A NORTHERN STREAM TROUGH DIGGING SOUTH FROM
CANADA AND TRAVERSING THE UPPER MIDWEST BY TUESDAY IN A POSITIVELY
TILTED FASHION. THE 00Z GEM AND 00Z UKMET ARE THE MOST PROGRESSIVE
SOLNS...WITH THE 12Z NAM/12Z GFS AND 00Z ECMWF A BIT SLOWER. THE
LATEST GEFS MEAN/ECENS MEAN AND ESP THE SREF MEAN FAVOR A SLOWER
EVOLUTION. WILL PREFER A BLEND OF THE GFS AND ECMWF ATTM.


...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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