Prognostic Meteorological Discussion
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FXUS10 KWNH 051654
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1154 AM EST MON DEC 05 2016

VALID DEC 05/1200 UTC THRU DEC 09/0000 UTC

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

12Z MODEL EVALUATION INCLUDING INITIAL PREFERENCES AND FORECAST
CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
~
MODEL INITIALIZATION ERRORS APPEAR NEGLIGIBLE WITH RESPECT TO
THEIR FORECASTS


NORTHERN MEXICO CLOSED LOW EJECTING NORTHEASTWARD TOWARDS THE EAST
COAST
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
~~~~~
PREFERENCE: 12Z ECMWF/GFS/UKMET COMPROMISE
CONFIDENCE: NEAR AVERAGE

THE UPPER LEVEL LOW CURRENTLY OVER NORTHERN MEXICO IS FORECAST TO
TRACK NORTHEASTWARD AND EVOLVE INTO A PROGRESSIVE OPEN WAVE ALOFT
AS IT BEGINS TO WEAKEN/FILL.  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 INTENSIFIES OFFSHORE LATER
IN THE PERIOD.

THE NAM WAS A BIT NORTH OF THE 05/00Z UKMET/ECMWF AND THE 05/12Z
GFS BY THE TIME THE VORT REACHES THE MID ATLANTIC COAST.  WHILE
NOT TERRIBLY FAR FROM THE CONSENSUS VALUE...THE 05/12Z NAM WAS
MORE COMPACT AND STRONGER THAN THE OTHER GUIDANCE.


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

A NEGATIVELY TILTED NORTHERN STREAM SHORTWAVE CURRENTLY CENTERED
OVER QUE WITH A LOBE OF VORTICITY EXTENDING ACROSS PARTS OF NEW
ENGLAND WILL CONTINUE TO SHEAR AS IT MOVES EAST/NORTHEAST.  THE
12Z NCEP MODELS APPEARED TO HANDLE THIS FEATURE IN A SIMILAR
FASHION...SO A GENERAL MODEL BLEND SHOULD CONTINUE TO BE FINE
HERE.


SOUTHERN CANADA CLOSED LOW WITH SURFACE LOW DEVELOPMENT OVER
NORTHERN PLAINS
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
~~~~~~~~~
PREFERENCE: 05/12Z NCEP RUNS AND THE 05/00Z UKMET BLEND
CONFIDENCE: SLIGHTLY BELOW AVERAGE

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

GIVEN THE DOWNSTREAM UPPER LEVEL CONFIGURATION, THE TIMING OF THIS
SHORTWAVE WILL DETERMINE THE MAGNITUDE OF DEEPENING OVER THE
EASTERN DAKOTAS AND MINNESOTA BY EARLY TUESDAY.

THE 00Z CMC IS CLOSER TO THE MODEL CONSENSUS WITH THE UPPER LOW
TUESDAY NIGHT COMPARED TO ITS EARLIER RUN, BUT STILL MORE
AMPLIFIED COMPARED TO THE OTHER OVERNIGHT GUIDANCE AND THE 12Z
NCEP RUNS.


SHORTWAVE TROUGH CROSSING THE GREAT BASIN TUESDAY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 05/00Z UKMET/ECMWF AND 05/12Z NCEP BLEND
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

AN UPPER LOW OVER THE GULF OF ALASKA WILL BEGIN TO SHEAR OUT AS IT
HEADS TOWARDS BRITISH COLUMBIA TODAY AND TONIGHT.  THE SHORTWAVE
ENERGY ASSOCIATED WITH THIS IS EXPECTED TO CROSS THE PACIFIC
NORTHWEST BEFORE SETTLING ACROSS THE GREAT BASIN ON TUESDAY, AND
THEN EJECT ACROSS THE CENTRAL PLAINS WEDNESDAY.

THE 12Z NCEP MODELS ARE MORE AGGRESSIVE IN ROTATING SHORTWAVE
ENERGY AROUND THE BASE OF THE LARGER MID/UPPER LEVEL CYCLONE.  THE
06/00Z EC MEAN REMAINED MORE PROGRESSIVE INITIALLY ON WITH THIS
SHORTWAVE THAN THE OPERATIONAL RUN OF THE ECMWF...BUT THE
DIFFERENCES IRON THEMSELVES OUT PRETTY QUICKLY LATE DAY 2 INTO DAY
3.

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

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

BANN

$$





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