Prognostic Meteorological Discussion
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000
FXUS10 KWNH 170506
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1206 AM EST WED DEC 17 2014

VALID DEC 17/0000 UTC THRU DEC 20/1200 UTC

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

==================================================
00Z NAM/GFS EVALUATION AND PRELIMINARY PREFERENCES
==================================================
NAM/GFS INITIALIZATION ERRORS DO NOT APPEAR TO
SIGNIFICANTLY AFFECT THEIR LARGE SCALE OUTPUT.
==================================================

...PACIFIC LEAD SHORTWAVES REACHING THE NORTHERN AND SOUTHERN
PLAINS THU...

PREFERENCE: BLEND OF THE OPERATIONAL MODELS...EXCLUDING THE
CANADIAN

A TROUGH AND SMALL CLOSED LOW WAS ENTERING THE DESERT SOUTHWEST
EARLY WEDNESDAY. THIS SYSTEM WILL OPEN AND DE-AMPLIFY AS IT HEADS
EAST...WITH A NORTHERN STREAM SHORTWAVE DRAGGING IT ALONG. THE 12Z
CANADIAN IS THE FLATTEST SOLUTION IN THE SOUTHERN STREAM AND
SLOWEST SOLUTION OF NORTH. THE REMAINING MODELS ARE REASONABLY
WELL CLUSTERED TOWARD A SOLUTION THAT AT LEAST SHOWS A DEFINABLE
SHORTWAVE IN THE SOUTHERN STREAM AS THE ENERGY ADVANCES TOWARD THE
OHIO VALLEY.


...DEEPER SHORTWAVES YIELDING A TROUGH ALONG THE LENGTH OF THE
MISSISSIPPI BY SAT...
...ASSOCIATED SURFACE WAVE AND PRECIPITATION FROM TEXAS EASTWARD...

PREFERENCE: BLEND OF 00Z NAM/GFS WITH 12Z ECMWF

THE MODELS ARE REASONABLY WELL CLUSTERED. THE 12Z UKMET WAS
SOMEWHAT SLOW AND THE CANADIAN WAS FAST. THE MOST RECENT
NAM/GFS/ECMWF RUNS CLUSTER VERY WELL AT THE SURFACE AND MODERATELY
WELL ALOFT. TRENDS THAT SHOW UP IN THE GFS HAVE BEEN FAIRLY
RELIABLE IN RECENT DAYS. THE 00Z RUN TRENDED TOWARD BEING DEEPER
AND MORE SHARPLY DEFINED WITH A NORTHERN STREAM COMPANION TROUGH
WHICH DIGS TOWARD THE MID MISSOURI VALLEY ON DAY 3. THIS PUSHES
THE MID LEVEL HEIGHT FALLS ALONG A LITTLE MORE QUICKLY ACROSS THE
SOUTHEAST STATES. THE 00Z PARALLEL GFS ALSO INDICATED THIS. ON THE
OTHER HAND...WE STILL RECOMMEND WEIGHTING SOLUTIONS BACK TOWARD
THE SLOWER NAM/ECMWF GIVEN THE UNCERTAINTY AS TO WHERE/WHEN/AND
HOW STRONGLY SYSTEMS WILL SPIN UP IN THIS ENERGETIC ZONAL FLOW
REGIME.


...WESTERN U.S. ON DAYS 2/3...

PREFERENCE: BLEND OF 00Z NAM/GFS WITH 12Z ECMWF

ENERGETIC FLOW OFF THE PACIFIC CONTINUES TO SPLIT INTO TWO
STREAMS...WITH THE SOUTHERN STREAM BEING STRONGER. BUT THE
SPLITTING IS VERY SLOW TO OCCUR GIVEN A PREPONDERANCE OF WESTERLY
FLOW IN BOTH STREAMS...SUCH THAT IT IS DIFFICULT TO PICK OUT
INDIVIDUAL SYSTEMS UNTIL THEY AMPLIFY AND BECOME BETTER DEFINED.
ONE SUCH SYSTEM SHOWS UP ON DAY 3 OVER MONTANA...AND ANOTHER SUCH
SYSTEM SHOWS UP ON DAY 4 IN THE SOUTHWEST STATES/SOUTHERN ROCKIES.
WPC MEDIUM RANGE PREFERRED THE ECMWF ENSEMBLE MEAN. TRENDS IN THE
GFS ARE TOWARD FASTER SOLUTIONS RELATIVE TO THE ECMWF ENSEMBLE
MEAN. THIS MAY HAVE SOME MERIT GIVEN THE MORE RECENT 18Z AND 00Z
INITIALIZATION...BUT THE 00Z GFS MAY BE TOO FAST BY DAY 4 AS IT
BREAKS CONTINUITY FROM THE 18Z GEFS MEAN AND MORE LAZILY SHARPENS
THE SOUTHERN STREAM TROUGH. ODDLY...THE BREAK IN CONTINUITY REALLY
DOES NOT SHOW UP DURING DAY 3. AT THAT TIME...CERTAINLY THE 12Z
UKMET APPEARED TOO FAST AND THE 12Z CANADIAN IS ON ITS WAY TO
BECOMING A SLOW AND DEEP OUTLIER. THIS LEAVES THE NAM/GFS/ECMWF
SOMEWHERE IN THE MIDDLE...AND BLENDING THEIR OUTPUT THROUGH DAY 3
WILL YIELD A CONSENSUS CLOSE TO THE ECMWF ENSEMBLE MEAN.


...GREAT LAKES/NORTHEAST...

PREFERENCE: BLEND OF 00Z GFS/12Z ECMWF

THE IMPACTS FROM THIS SYSTEM ARE MAINLY CONFINED TO DAYS 1 AND 2.
THE MODELS SHOW GOOD AGREEMENT THROUGH THAT TIME EXCEPT THAT THE
00Z NAM IS SLOW OR WEST OF CONSENSUS. THE 00Z GFS TRENDED FASTER
THAN ITS PREVIOUS RUNS. THE PARALLEL GFS MORE OR LESS MAINTAINED
CONTINUITY WITH THE PREVIOUS RUNS. THERE IS SOME SUPPORT FOR
FASTER SOLUTIONS FROM THE UKMET AND CANADIAN...BUT AGAIN THESE
DIFFERENCES MAINLY AFFECT AREAS OFFSHORE AND OVER FAR EASTERN
CANADA. KEEPING WITH OUR PREVIOUS PREFERENCE...A BLEND OF THE
GFS/ECMWF IS STILL WELL REPRESENTATIVE OF CONSENSUS.

...MODEL TREND GRAPHICS AT
www.wpc.ncep.noaa.gov/html/model2.shtml...
...500 MB FORECASTS AT
www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml...

BURKE
$$




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