Prognostic Meteorological Discussion
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000
FXUS10 KWNH 241606
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1106 AM 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 AND GFS


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

PREFERENCE: NON-GEM CONSENSUS
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 00Z GEM IS ON THE SLOWER END OF THE GUIDANCE
WITH RESPECT TO THE EXITING SHORTWAVE ENERGY. THE REMAINING MODELS
ARE REASONABLY WELL CLUSTERED WITH TIMING AND DEPTH. SO...A
NON-GEM CONSENSUS SOLN IS PREFERRED.


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

PREFERENCE: BLEND OF THE 00Z ECMWF AND 00Z GEM
CONFIDENCE: SLIGHTLY BELOW AVERAGE

SIMILAR TO THE LAST UPPER TROUGH TO DIG ACROSS THE WESTERN
U.S....THE TREND 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 00Z ECMWF/00Z UKMET AND 00Z GEM
ALL SLOWER. THE TREND IN THE NAM AND GFS THOUGH IS TOWARD THE
SLOWER NON-NCEP CONSENSUS...AND SO WILL MAINTAIN PREV CONTINUITY
AND PREFER A BLEND OF THE GEM AND ECMWF WHICH SHOW RATHER STRONG
MODEL CLUSTERING.


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

PREFERENCE: BLEND OF THE 12Z GFS AND 00Z 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 00Z UKMET. THE 00Z
ECMWF AND 12Z GFS ARE A BIT SLOWER BUT RATHER WELL CLUSTERED
OVERALL. THE 00Z 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: GENERAL MODEL COMPROMISE
CONFIDENCE: ABOVE 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. GIVEN THESE TRENDS AND CURRENTLY LITTLE
ENSEMBLE SUPPORT FOR A STRONGER WAVE...THE PREFERENCE WILL BE
TOWARD THE GLOBAL MODEL CONSENSUS WHICH CURRENTLY FAVORS A RATHER
FLAT SURFACE WAVE. THERE IS NOT A PARTICULARLY LARGE AMOUNT OF
SPREAD WITH TIMING OF THE WAVE EITHER...SO A GENERAL MODEL
COMPROMISE WILL BE PREFERRED TO RESOLVE THE SMALLER SCALE DIFFS
THAT DO EXIST.


...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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