Prognostic Meteorological Discussion
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FXUS10 KWNH 060506
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MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1205 AM EST TUE DEC 6 2016

VALID DEC 6/0000 UTC THRU DEC 9/1200 UTC

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

00Z NAM/GFS MODEL EVALUATION INCLUDING PREFERENCES AND FORECAST
CONFIDENCE

MODEL INITIALIZATION ERRORS APPEAR NEGLIGIBLE WITH RESPECT TO
THEIR FORECASTS


STRONG SHORTWAVE OVER TEXAS MOVING NORTHEASTWARD TOWARDS THE EAST
COAST
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
~~~~

PREFERENCE: 12Z ECMWF/00Z GFS/00Z NAM COMPROMISE
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

THE UPPER LEVEL SHORTWAVE TROUGH OVER EASTERN TEXAS IS FORECAST TO
TRACK NORTHEASTWARD AND REMAIN A PROGRESSIVE OPEN WAVE ALOFT.  IT
SHOULD THEN WEAKEN ONCE IT EMERGES OVER THE WESTERN ATLANTIC SINCE
IT WILL BE ENTERING A RIDGE AXIS.  AT THE SURFACE, A SURFACE LOW
WILL TRACK INLAND WEST OF THE APPALACHIANS WHILE A SECOND SURFACE
LOW FORMS NEAR THE NORTH CAROLINA COAST AND THEN MOVES OFFSHORE.

THE 12Z UKMET APPEARS A LITTLE MORE AMPLIFIED WITH THE SHORTWAVE
ENERGY AS IT TRACKS FROM THE DEEP SOUTH TO THE MID-ATLANTIC REGION
BUT IS SIMILAR WITH TIMING.  THE 12Z CMC SHOWS SLIGHTLY MORE
RIDGING DOWNSTREAM FROM THE TROUGH.  THE 00Z NAM HAS COME INTO
BETTER AGREEMENT WITH THE MODEL CONSENSUS COMPARED TO ITS EARLIER
RUN.


SHEARING NORTHEASTERN U.S. SHORTWAVE EXITING TUESDAY MORNING
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: ABOVE AVERAGE

A NEGATIVELY TILTED NORTHERN STREAM SHORTWAVE CURRENTLY CENTERED
OVER QUEBEC AND MAINE WITH A LOBE OF VORTICITY EXTENDING ACROSS
PARTS OF NEW ENGLAND WILL CONTINUE TO SHEAR OUT AS IT MOVES
EASTWARD.  THE CURRENT MODEL SUITE IS IN GOOD AGREEMENT ON THIS
FEATURE AND THEREFORE A GENERAL MODEL BLEND IS RECOMMENDED.


SOUTHERN CANADA CLOSED LOW WITH SURFACE LOW OVER UPPER MIDWEST
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

PREFERENCE: 00Z GFS/12Z ECMWF BLEND
CONFIDENCE: NEAR AVERAGE

SHORTWAVE ENERGY CURRENTLY OVER THE NORTHERN PLAINS WILL CONTINUE
TO ROTATE AROUND THE SOUTHERN PERIPHERY OF THE UPPER LEVEL VORTEX
THAT IS FORMING OVER SASKATCHEWAN AND MANITOBA.  THE COLD FRONT
ASSOCIATED WITH THE SURFACE LOW WILL USHER IN THE FIRST NOTEWORTHY
ARCTIC AIRMASS OF THE SEASON.

THE 12Z UKMET IS FARTHER SOUTH WITH THE SURFACE LOW OVER NORTHERN
MINNESOTA COMPARED TO THE MODEL CONSENSUS, AND ALSO SHARPER WITH
THE SURFACE COLD FRONT.  THERE APPEARS TO BE GOOD OVERALL
AGREEMENT WITH THE TIMING OF THE COLD FRONTAL PASSAGE ACROSS THE
CENTRAL AND EASTERN U.S. EARLY IN THE PERIOD.  THERE IS MORE
SPREAD WITH THE SECONDARY COLD FRONT THAT IS FORECAST TO CROSS THE
GREAT LAKES AND OHIO VALLEY LATER IN THE PERIOD, WITH THE NAM
STRONGER WITH THIS FRONT.


SHORTWAVE TROUGH TRACKING FROM THE GREAT BASIN TO THE CENTRAL
PLAINS
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
~

PREFERENCE: 00Z NAM/00Z GFS/18Z GEFS MEAN
CONFIDENCE: NEAR AVERAGE

A SHORTWAVE TROUGH NEAR VANCOUVER ISLAND AT THE BEGINNING OF THE
FORECAST PERIOD WILL CROSS THE PACIFIC NORTHWEST BEFORE SETTLING
ACROSS THE GREAT BASIN ON TUESDAY EVENING, AND THEN EJECT ACROSS
THE CENTRAL PLAINS WEDNESDAY AS A BROAD UPPER LEVEL TROUGH.

THE 00Z NAM IS A BIT MORE PRONOUNCED WITH THE TROUGH AXIS, AND THE
00Z GFS IS CLOSE TO THAT SOLUTION.  GIVEN THE AMOUNT OF UPSTREAM
RIDGING OVER THE EASTERN PACIFIC DURING THIS TIME, WE THINK THE
NAM/GFS IDEA OF MARGINALLY LOWER HEIGHTS OVER THE ROCKIES AND
WESTERN HIGH PLAINS SEEMS MORE REASONABLE.


STORM SYSTEM APPROACHING THE PACIFIC NORTHWEST COAST BY FRIDAY
MORNING
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
~~~

PREFERENCE: 12Z EC MEAN/18Z GEFS MEAN BLEND
CONFIDENCE: BELOW AVERAGE

THE GREATEST AMOUNT OF MODEL DISAGREEMENT DURING THE SHORT-RANGE
FORECAST PERIOD IS ASSOCIATED WITH A STRONG LOW PRESSURE SYSTEM
TRACKING TOWARDS THE PACIFIC NORTHWEST COAST BY THURSDAY NIGHT.
THE GFS IS THE FASTEST SOLUTION BRINGING THE SURFACE LOW CLOSEST
TO THE COAST BY 00Z FRIDAY.  THE ECMWF APPEARS TOO WEAK WITH THE
LOW AND MORE ELONGATED THAN THE OTHER SOLUTIONS.  THE UKMET AND
NAM ARE AMONG THE STRONGEST SOLUTIONS.  UNTIL BETTER AGREEMENT
BECOMES APPARENT, AN ENSEMBLE APPROACH FOR THIS SYSTEM IS PROBABLY
BEST FOR NOW.

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

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

HAMRICK

$$





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