Prognostic Meteorological Discussion
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079
FXUS10 KWNH 101657
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1157 AM EST SAT DEC 10 2016

VALID DEC 10/1200 UTC THRU DEC 14/0000 UTC

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

12Z NAM/GFS EVALUATION ALONG WITH PRELIMINARY PREFERENCES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

LOW AMPLITUDE SHORTWAVE CROSSING THE GREAT LAKES AND NEW ENGLAND
  TODAY AND TONIGHT
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL COMPROMISE
CONFIDENCE: ABOVE AVERAGE

THE MODELS CONTINUE TO SHOW SIMILARLY WITH THIS SYSTEM.


PROGRESSIVE SHORTWAVE CROSSING THE NRN ROCKIES TODAY...PASSING OVER
  THE GREAT LAKES EARLY MON WITH ACCOMPANYING SURFACE LOW/FRONT
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF THE 12Z GFS / 00Z ECMWF
CONFIDENCE: AVERAGE

MINOR TO MODERATE SPREAD REMAINS IN THE LATEST SPAGHETTI ENSEMBLE
HEIGHTS FOR SUN NIGHT THROUGH MON...BUT THERE HAS BEEN SOME
CONVERGENCE OVER THE PAST 24 HOURS. THE OVERALL TREND HAS BEEN FOR
A FLATTER AND SLIGHTLY MORE PROGRESSIVE MID-LEVEL SHORTWAVE...BUT
THE 12Z NAM/GFS REMAIN ON THE DEEPER SIDE OF THE SPREAD...MOST
NOTABLY WITH THE NAM WHICH SHOWS THE MOST PHASING OF ENERGY IN THE
MID-LEVELS.

ON THE CONTRARY TO THE STRONGER NAM/GFS...IS THE FLATTER 00Z
ECMWF/UKMET...WITH THE UKMET FLATTEST. THE ECMWF HAS BEEN FLIP
FLOPPING BETWEEN SLIGHTLY STRONGER/WEAKER REGARDING THE SHORTWAVE
WITH THE MOST RECENT 00Z ECMWF A BIT FLATTER. THIS IS REFLECTED AT
THE SURFACE AS WELL WITH THE GFS SHOWING A STRONGER PARENT WAVE
CROSSING THE GREAT LAKES INTO NEW ENGLAND. THE AVERAGE OF THE
ENSEMBLE MEAN STRENGTHS SUPPORTS A STRENGTH BETWEEN THE 12Z GFS
AND 00Z ECMWF.

REGARDING SURFACE LOW DEVELOPMENT NEAR THE COAST OF MAINE ON
MON...THE 12Z GFS IS TOWARD THE NRN AND STRONGER SIDE OF THE
LATEST ENSEMBLE SPREAD. A POSITION CLOSER TO THE 00Z ECMWF SHOULD
BE GIVEN MORE WEIGHT THAN THE 12Z GFS.


CONTINUED ONSHORE FLOW INTO THE WEST COAST FROM SUN-TUE
EXPECTED FRONTAL WAVE APPROACHING THE N-CNTRL CA COAST ON TUE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z GFS / 00Z ECMWF BLEND
CONFIDENCE: BELOW AVERAGE

WHILE DETERMINISTIC/ENSEMBLE TRENDS HAVE SHOWN MORE SEPARATION
BETWEEN A LARGE VORTEX DROPPING SOUTH THROUGH CANADA AND A LIKELY
DEVELOPING CLOSED LOW WEST OF THE PACIFIC NORTHWEST COAST ON
MON...THERE REMAINS SIGNIFICANT SPREAD IN THE ENSEMBLES.
CURRENTLY...THE 00Z ECMWF MEAN IS FARTHER OFFSHORE COMPARED TO THE
00/06Z GEFS MEAN BUT THE DETERMINISTIC 00Z ECMWF AND 12Z GFS ARE
CLOSER TO ONE ANOTHER THAN THEIR ENSEMBLE MEANS.

ONLY THE 00Z CMC STANDS OUT SIGNIFICANTLY FROM THESE TWO CAMPS
THOUGH...AND WITH AN EXPECTED SURFACE LOW FORECAST TO REACH THE
N-CNTRL COAST OF CALIFORNIA ON TUE. A BLEND OF THE 12Z NAM...00Z
ECMWF AND 12Z GFS SPLITS THE DIFFERENCES AMONG THE SURFACE
LOW...WITH A 12Z GFS/00Z ECMWF BLEND CONSIDERED BEST FOR THE
OFFSHORE SYSTEM.


LARGE VORTEX SINKING SSEWD THROUGH S-CNTRL CANADA MON/TUE WITH
  ASSOCIATED ARCTIC COLD FRONT
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON 00Z CMC BLEND
CONFIDENCE:

ONLY THE CMC...WHICH IS LESS PROGRESSIVE WITH A LARGE UPPER LEVEL
CLOSED LOW DROPPING SSE THROUGH S-CNTRL CANADA...DIFFERS
SIGNIFICANTLY FROM THE REMAINING...WELL CLUSTERED MODEL GUIDANCE.

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

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

OTTO



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