Prognostic Meteorological Discussion
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FXUS10 KWNH 051840
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
139 PM 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 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 UKMET/ECMWF/GFS BY THE TIME THE
VORT REACHES THE MID ATLANTIC COAST.  WHILE NOT TERRIBLY FAR FROM
THE CONSENSUS LATITUDE...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 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/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 12Z NCEP
MODELS WERE MORE AGGRESSIVE IN ROTATING SHORTWAVE ENERGY AROUND
THE BASE OF THE LARGER MID/UPPER LEVEL CYCLONE.  DESPITE THE
DIFFERENT WAYS IN WHICH THE MODELS HANDLE THE SHORTWAVE
ENERGY...MANY OF THE DIFFERENCES OVER THE LOWER 48 IRON THEMSELVES
OUT BY THE END OF DAY 3.


...SHORTWAVE TROUGH CROSSING THE GREAT BASIN TUE TO THE CENTRAL
ROCKIES WED...

PREFERENCE: 05/12Z UKMET/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 GUIDANCE SEPARATED THEMSELVES FROM THE 00Z NON NCEP
GUIDANCE BY BEING MORE AMPLIFIED ONCE THE ENERGY REACHES THE
CENTRAL ROCKIES LATE WEDNESDAY AND THURSDAY.  THE NON NCEP
GUIDANCE GENERALLY KEPT TO THE IDEA SHOWN IN THEIR PREVIOUS RUNS.
GIVEN THE AMOUNT OF UPSTREAM RIDGING...THINK THE NCEP IDEA OF
MARGINALLY LOWER HEIGHTS EAST OF THE CENTRAL ROCKIES FITS BETTER.


...SYSTEM APPROACHING THE PAC NW COAST BY END OF DAY 3...

PREFERENCE: NON 12Z GFS BLEND
CONFIDENCE: AVERAGE

THE MODELS WERE IN GENERALLY GOOD AGREEMENT WITH THE APPROACH OF
THE NEXT TROF AND ASSOCIATED PRECIPITATION.  THE ONE EXCEPTION WAS
THE 12Z GFS WHICH WAS CONSIDERABLY FASTER.  GIVEN THE DOWNSTREAM
FLOW PATTERN...THINK THAT THE WAVELENGTHS INVOLVED WITH ARGUE
AGAINST THE GFS.  THE LACK OF A WELL DEFINED JET NOSING IN FROM
THE ERN NOPAC SEEMS WHICH WOULD AID THE LOWERING OF HEIGHTS OVER
THE PAC NW ALSO ARGUES AGAINST THE GFS IDEA.


...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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