Prognostic Meteorological Discussion
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FXUS10 KWNH 241851
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
150 PM EST WED DEC 24 2014

VALID DEC 24/1200 UTC THRU DEC 28/0000 UTC

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

12Z MODEL EVALUATION...INCLUDING THE NAM/GFS/UKMET/GEM AND THE
ECMWF

...INTENSIFYING LOW LIFTING THROUGH THE GREAT LAKES...

PREFERENCE: GENERAL MODEL COMPROMISE
CONFIDENCE: ABOVE AVERAGE

THE LATEST MODELS ARE IN VERY GOOD AGREEMENT IN TAKING THE
SHORTWAVE TROUGH CURRENTLY OVER THE LOWER AND MID MS VALLEY
NORTHEAST INTO THE LOWER GREAT LAKES REGION BY LATER TONIGHT AND
EARLY CHRISTMAS DAY. THIS WILL ALLOW SURFACE LOW PRESSURE TO LIFT
NORTH THROUGH THE OH VALLEY AND GRADUALLY INTO SOUTHEAST ONTARIO
BY EARLY THURS. THE MODELS ARE IN SUFFICIENTLY STRONG ENOUGH
AGREEMENT NOW THAT A GENERAL MODEL COMPROMISE CAN BE PREFERRED.


...UPPER TROUGH DIGGING ACROSS THE INTERMOUNTAIN WEST/FOUR CORNERS
REGION THROUGH FRI...

PREFERENCE: 12Z ECMWF
CONFIDENCE: BELOW AVERAGE

SIMILAR TO THE LAST UPPER TROUGH TO DIG ACROSS THE WESTERN
U.S....THE TREND OVERALL IN THE GUIDANCE IS TO BE SLOWER BY FRI
WITH THE HEIGHT FALLS. THE 12Z NAM AND 12Z GFS THOUGH CONTINUE TO
BRING MORE ENERGY FARTHER EAST OUT ACROSS THE PLAINS AND MIDWEST
BY LATER FRI AND FRI NIGHT...WITH THE 12Z UKMET AND 12Z GEM BOTH
THE SLOWEST SOLNS. ONE CONFLICTING TREND TO NOTE WITH THE 12Z
GUIDANCE IS THAT THE 12Z ECMWF TRENDED A BIT MORE PROGRESSIVE BY
LATER SAT IN TAKING ENERGY EAST ACROSS THE CENTRAL PLAINS. IT
SPLITS THE DIFF BETWEEN THE SLOWER UKMET/GEM CAMP AND THE MORE
PROGRESSIVE NAM/GFS CAMP. GIVEN THE OVERALL MODEL SPREAD...THE
ECMWF WILL BE PREFERRED...AND IT AT LEAST DOES HAVE THE SUPPORT OF
THE 12Z GEFS MEAN IS A BIT SLOWER THAN THE NAM/GFS SOLNS.
CONFIDENCE IS LIMITED THOUGH SINCE THERE HAS BEEN A NOTABLE BREAK
IN CONTINUITY WITH THE ECMWF.


...SHORTWAVE TROUGH DIGGING TOWARD THE PACIFIC NORTHWEST ON SAT...

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

THE MODELS INDICATE A SHORTWAVE TROUGH DIGGING SOUTHEAST FROM THE
GULF OF AK AND INTO SOUTHWEST BRITISH COLUMBIA AND THE PACIFIC
NORTHWEST BY LATER SAT. THE 12Z NAM IS THE FASTEST SOLN TO BRING
THE ENERGY SOUTHEAST FOLLOWED CLOSELY BY THE 12Z UKMET. THE 12Z
ECMWF AND 12Z GFS ARE A BIT SLOWER BUT RATHER WELL CLUSTERED
OVERALL. THE 12Z GEM IS A FLAT/WEAK OUTLIER SOLN. BASED ON
STRONGER MODEL CLUSTERING AND ENSEMBLE SUPPORT...A BLEND OF THE
GFS AND ECMWF WILL BE PREFERRED.


...SURFACE LOW LIFTING NORTHEAST ACROSS THE MIDWEST ON FRI...

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

MODEL TRENDS OVER THE PAST 24 HOURS HAVE BEEN TO WEAKEN AN
EASTWARD PROGRESSING SURFACE LOW THAT TRACKS THROUGH THE PLAINS
ALONG A FRONT ON FRI. THIS IS DUE TO WEAKER TRENDS REGARDING A LOW
AMPLITUDE MID-LEVEL SHORTWAVE FORECAST TO EJECT OUT INTO THE
PLAINS...OUT AHEAD OF A LARGER SCALE TROUGH ACROSS THE SOUTHWEST
THURS NIGHT THROUGH FRI. THE 12Z NAM THOUGH NOW APPEARS TO BE TOO
STRONG WITH THE SURFACE LOW BY THE END OF THE PERIOD AS IT EXITS
THE UPPER GREAT LAKES REGION. THE 12Z GEM AND 12Z UKMET ARE THE
WEAKEST SOLNS...WITH THE 12Z GFS AND 12Z ECMWF SPLITTING THE DIFF.
BASED ON THE MODEL SPREAD AND BETTER CLUSTERING...WILL PREFER A
BLEND OF THE GFS AND ECMWF.


...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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