Prognostic Meteorological Discussion
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000
FXUS10 KWNH 041842
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
141 PM EST SUN DEC 04 2016

VALID DEC 04/1200 UTC THRU DEC 08/0000 UTC

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

12Z MODEL EVALUATION INCLUDING PREFERENCES AND FORECAST CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

WESTERN MEXICO CLOSED LOW EJECTING NORTHEASTWARD WITH MILLER-B
SETUP OVER EASTERN US BY TUES/WED
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z UKMET/ECMWF/GFS BLEND
CONFIDENCE: SLIGHTLY BELOW AVERAGE

SPREAD CONTINUES TO REDUCE WITH TIME AS THE SYSTEM BECOMES MORE
FOCUSED WITHIN THE DATA NETWORK AND STARTS TO LIFT OUT OF MEXICO.
THE 00Z ECMWF/UKMET AND ECENS MEAN HAVE BE MORE CONSISTENT AND
STABLE OVER THE LAST DAY OR SO NOW THAT THE ECENS MEAN HAS SLOWED.
 THE 12Z NAM TRENDED SLOWER AND MORE IN SYNC WITH THESE SOLUTIONS.
 THOUGH IN THE FINAL STAGES BEFORE FULLY WEAKENING OUT THE NAM
TRACKS A BIT NORTH RATHER THAN SHIFTING EAST LIKE THE UKMET/ECMWF
LEADING TO MINOR DIFFERENCES NOTED BY THE END OF DAY 3 MAKING IT A
BIT LESS FAVORABLE AT THAT TIME FRAME YET STILL USEFUL IN THE
BLEND/CONFIDENCE BUILDER.

THE 00Z CMC IS QUICK TO WEAKEN AND IS INFLUENCED NEGATIVELY BY THE
OVER AMPLIFIED AND EASTWARD SHIFTED UPPER LOW DEVELOPING IN THE
UPPER MIDWEST.  THIS MAKES IT LESS DESIRABLE AS A WHOLE.  THE 12Z
GFS WHILE INDICATING SOME SLIGHTLY FASTER TREND TOWARD THE COMMON
SOLUTION REMAINS SLOW PARTICULARLY AFFECTING DIFFERENCES ACROSS
THE TN/UPPER OH VALLEY/APPALACHIANS AND LESSER SO OVER THE
SOUTHEAST COASTAL PLAIN.  ALL CONSIDERED THOUGH...A 00Z
ECMWF/UKMET WEIGHTED BLEND WITH THE 12Z NAM IS WPC PREFERENCE AT
SLIGHTLY ABOVE AVERAGE CONFIDENCE.

19Z UPDATE: BOTH 12Z ECMWF AND UKMET TRENDED SLOWER WITH THE WAVE
AS A WHOLE LEADING TO A FURTHER EAST SURFACE TRACK WITH THE LOW
NOW IN THE E TN VALLEY.  WHILE NOT AS SLOW AS THE GFS THESE TWO
SHIFTING SLOWER CASTS SOME FURTHER DOUBT OVERALL.  THE 12Z CMC
CONTINUES TO BE WEAKER WITH THE WAVE BUT REMAINS A FASTER SOLUTION
WITH THE REMAINING 12Z NAM.   GIVEN THE THREE SLOWER ARE
TRADITIONALLY MORE RELIABLE WILL SHIFT TO SUPPORT THIS CHANGE BUT
LOWER CONFIDENCE TO SLIGHTLY BELOW AVERAGE GIVEN THIS MAY BE A RUN
TO RUN OSCILLATION AS THE WAVE MOVES OUT OF THE MEXICAN PLATEAU.



NORTHERN U.S. SHORTWAVE SHEARING THROUGH NEW ENGLAND BY MONDAY
NIGHT
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: ABOVE AVERAGE

A PROGRESSIVE NORTHERN STREAM SHORTWAVE TROUGH OVER THE WESTERN
MIDWEST THIS MORNING IS FORECAST TO TRACK RAPIDLY EASTWARD ACROSS
THE GREAT LAKES WHILE ACQUIRING NEGATIVE TILT AS IT SHEARS WEST TO
EAST OVER THE UPPER LEVEL RIDGE DIRECTLY AHEAD OF IT AND BY THE
TIME IT REACHES NEW ENGLAND IT BECOMES MORE ZONALLY ORIENTED.
MODELS INDICATE SOLID AGREEMENT TO SUPPORT A GENERAL MODEL BLEND
AT ABOVE AVERAGE CONFIDENCE.

19Z UPDATE: LITTLE CHANGE WITH THE EVOLUTION OF THIS SYSTEM WITH
THE 12Z NON-NCEP SOLUTIONS SUPPORTS GENERAL MODEL BLEND AT ABOVE
AVERAGE CONFIDENCE AS WELL.


SOUTHERN CANADA CLOSED LOW WITH SURFACE LOW DEVELOPMENT OVER
NORTHERN PLAINS BY TUES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z NAM/GFS/UKMET BLEND (INCL. 12Z GEFS/00Z ECENS
MEAN)
CONFIDENCE: AVERAGE TO SLIGHTLY BELOW AVERAGE

SHORTWAVE ENERGY CURRENTLY OVER SW BC WILL CONTINUE TO DROP SE
ACROSS THE US ROCKIES AND BY ROTATING AROUND THE SOUTHERN
PERIPHERY OF THE UPPER LEVEL PIVOT THAT IS STARTING TO FORM OVER
SASKATCHEWAN.  GIVEN DOWNSTREAM UPPER LEVEL CONFIGURATION...THE
TIMING OF THIS SHORTWAVE WILL DETERMINE THE MAGNITUDE OF RAPID
DEEPENING OVER THE RED RIVER VALLEY BY EARLY TUESDAY.  THE 12Z GFS
CONTINUES TO BE THE FASTER SOLUTION AND AS SUCH WILL HAVE THE BEST
CONFIGURATION FOR A DEEPER MORE CONCENTRIC UPPER LOW EVOLUTION
WHILE WOBBLING EASTWARD EARLIER INTO NW/N CENT ONTARIO.  YET THE
12Z RUN HAS TRENDED A BIT SLOWER/WESTWARD WHICH APPEARS POSITIVE
TOWARD THE OVERALL SPREAD.   THE 00Z ECMWF IS SLOWER TO REACH THE
SE PERIPHERY OF THE UPPER LOW AND SO DEEPENS LATER AND SUPPORTS A
MORE ELONGATED E-W UPPER LEVEL PATTERN WHILE SUPPORTING A WOUND UP
SURFACE CIRCULATION FURTHER WEST FOR LONGER TIME.  WHILE THE GEFS
SOLUTIONS FOLLOW THE GFS WELL...THE 00Z ECENS MEMBERS SPLIT THE
DIFFERENCE OF THE TWO WITH THE OPERATIONAL ECMWF BEING ON THE
WESTERN THIRD OF SOLUTIONS.  THE 12Z NAM TRENDED A BIT FASTER AND
TIMES WELL WITH THE ECMWF THROUGH TUESDAY...BUT EVOLVES MORE
CONCENTRICALLY AND SHIFTS EASTWARD LIKE THE GFS (JUST SLOWER IN
TIME) ACTING AS A MIDDLE GROUND PROXY FOR THE TWO SOLUTIONS.

THE 00Z CMC IS SLOW BUT ALSO A CLEAR OUTLIER FORMING THE CLOSED
LOW OVER THE NW GREAT LAKES AND THE 00Z UKMET WHILE SIMILAR TO THE
ECMWF IS EVEN FURTHER SLOWER MAKING IT APPEAR ON THE FAR EXTREME
OF 00Z ECENS MEMBERS.  AS SUCH A BLEND OF THE 12Z NAM/GFS AND 00Z
ECMWF APPEARS TO BE A GOOD REPRESENTATION OF THE ENSEMBLE
SOLUTIONS THOUGH THE REMAINING SPREAD IS LARGE ENOUGH BASED ON
SUCH SHORT TIMING DIFFERENCES TO HAVE AN AVERAGE CONFIDENCE IN THE
BLEND COMING TO FRUITION.

19Z UPDATE: THE 12Z NON-NCEP SOLUTIONS ALL TRENDED TOWARD A DEEPER
MANIFESTATION OF THE UPPER LOW BY TUESDAY AFTERNOON...BUT BEING
SLOWER WITH THE TAIL END OF THE SHORTWAVE SWING THROUGH SUPPORTS
MORE OF A NEGATIVE TILT/ELONGATION OF THE TROF FAVORING THE TAIL
END VORT CENTER.  THE 12Z ECMWF IS MOST ROBUST OF THE TAIL END
WAVE...YET ALSO RETAINS THE STRONGEST LEAD PORTION OF THE WAVE
RESULTING IN THE MOST ELONGATED W-E TROF BY WED AFTERNOON...AND
AWAY FROM THE ENSEMBLE SOLUTIONS THAT FAVOR THE MORE CONCENTRIC
GFS SOLUTION...AND AS SUCH IS NO LONGER FAVORED IN THE BLEND.
THE 12Z CMC REMAINS QUITE SUPPRESSED AND FURTHER SOUTH.   THE 12Z
UKMET WHILE BEING SLOWER TO DEVELOP THE WAVE STILL COMPARED TO THE
GFS/ENSEMBLE MEANS...IS MOST SIMILAR WHILE SUPPORTING SOME HINTS
THE SLOWER/ELONGATED EVOLUTION.   WILL FAVOR THE 12Z GEFS/GFS/NAM
AND 00Z ECENS MEAN IN THE BLEND ALONG WITH A LOWER WEIGHTED 12Z
UKMET.  CONFIDENCE IS AVERAGE TO SLIGHTLY BELOW AVERAGE GIVEN THE
SPREAD DUE TO SMALL TIMING/ENERGY PLACEMENT DIFFERENCES IN THE
SHORTWAVE WITHIN THE BROADER LONGWAVE TROF.


SHORTWAVE TROUGH CROSSING THE GREAT BASIN LATE TUES AND INTO THE
CENTRAL PLAINS BY LATE WED
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z GFS/UKMET/ECMWF BLEND
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

THE GULF OF ALASKA UPPER LOW UNDER THE INFLUENCE OF A LARGER
GLOBAL SCALE TROUGH ACROSS NORTHWESTERN CANADA BEGINS TO SHEAR OUT
ALONG THE BRITISH COLUMBIA COAST ON MONDAY.  THE SHORTWAVE ENERGY
ASSOCIATED WITH THIS IS EXPECTED TO CROSS THE PACIFIC NORTHWEST
BEFORE SETTLING ACROSS THE GREAT BASIN ON TUESDAY AND EJECTING
INTO THE CENTRAL PLAINS BY WED.

TIMING OF THE WAVE SEEMS TO LEAD TO THE LARGEST SPREAD IN GUIDANCE
THOUGH AS THE WAVE EJECTS INTO THE PLAINS ON WED...THE MIDDLE
GROUND IN TIMING 12Z NAM IS MOST AMPLIFIED TYPICAL OF ITS KNOWN
DAY 3 NEGATIVE BIAS.  THE 12Z GFS TRENDED A BIT SLOWER THAN THE
06Z GFS/GEFS BUT REMAIN A BIT FASTER THAN THE MAJORITY OF OTHER
GUIDANCE.  THE 00Z ECMWF/UKMET ARE BOTH ON THE SLOWER SIDE BUT YET
WITHIN THE BULK OF ENSEMBLE SOLUTIONS AND BECOME A BIT MORE
AMPLIFIED AT 7H THOUGH NOT AS DRASTIC AS THE 12Z NAM.  THE 00Z CMC
IS SLOWER AND MORE BROAD THAN THE REST OF THE GUIDANCE.  AS SUCH
WILL SUPPORT AT 12Z GFS AND 00Z UKMET/ECMWF BLEND AT SLIGHTLY
ABOVE AVERAGE CONFIDENCE.

19Z UPDATE: LITTLE DIFFERENCES IN THE 12Z ECMWF/UKMET BOTH
CONTINUE TO SUPPORT THE INITIAL PREFERENCE. SIMILARLY THE 12Z CMC
REMAINS SLOWER AND MORE BROAD...KEEPING IT FROM THE PREFERENCE AT
THIS POINT AS WELL.


...MODEL TREND GRAPHICS AT
www.wpc.ncep.noaa.gov/html/model2.shtml...

...500 MB FORECASTS AT
www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml...

GALLINA

$$




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