Prognostic Meteorological Discussion
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000
FXUS10 KWNH 060655
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
154 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 FINAL MODEL EVALUATION INCLUDING PREFERENCES AND FORECAST
CONFIDENCE


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

PREFERENCE: NON-UKMET 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 00Z UKMET CONTINUES TO BE 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 00Z CMC SHOWS
LESS RIDGING DOWNSTREAM FROM THE TROUGH COMPARED TO ITS EARLIER
RUN.  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/00Z 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 00Z UKMET HAS COME INTO BETTER AGREEMENT WITH THE SURFACE LOW
OVER NORTHERN MINNESOTA COMPARED TO THE MODEL CONSENSUS.  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 GFS/00Z 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
GFS IDEA OF MARGINALLY LOWER HEIGHTS OVER THE ROCKIES AND WESTERN
HIGH PLAINS SEEMS MORE REASONABLE, BUT NOT TO THE SAME DEGREE AS
THE NAM


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

PREFERENCE: 12Z EC MEAN/00Z GEFS MEAN/00Z CMC 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 STILL APPEARS TOO WEAK WITH
THE LOW AND MORE ELONGATED THAN THE OTHER SOLUTIONS.  THE UKMET
AND NAM ARE AMONG THE STRONGEST SOLUTIONS.  THE 00Z CMC IS CLOSE
TO THE MODEL CONSENSUS IN TERMS OF PLACEMENT.  UNTIL BETTER
AGREEMENT BECOMES APPARENT, AN ENSEMBLE APPROACH FOR THIS SYSTEM
IS PROBABLY BEST FOR NOW, ALONG WITH SOME OF THE CMC.

...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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