Prognostic Meteorological Discussion
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000
FXUS10 KWNH 100451
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1150 PM EST FRI DEC 09 2016

VALID DEC 10/0000 UTC THRU DEC 13/1200 UTC

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

00Z NCEP MODEL EVALUATION ALONG WITH PRELIMINARY PREFERENCES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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

THE MODELS CONTINUE TO SHOW SIMILARLY WITH THIS SYSTEM.


PROGRESSIVE SHORTWAVE CROSSING THE NRN ROCKIES SAT AND PASSING OVER
  THE GREAT LAKES EARLY MON WITH ACCOMPANYING SURFACE LOW/FRONT
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF THE 10/00Z GFS AND 09/00Z ECMWF
CONFIDENCE: SLIGHTLY BELOW AVERAGE

MODEST SPREAD REMAINS IN THE LATEST SPAGHETTI ENSEMBLE HEIGHTS FOR
SUN NIGHT INTO MON...AND CONFIDENCE REMAINS BELOW AVERAGE.

DESPITE LOWER CONFIDENCE OVERALL...THERE WAS BETTER AGREEMENT
TOWARD THE MORE AMPLIFIED 10/00Z GFS AND 09/12Z ECMWF IDEA AS
COMPARED WITH THE SOMEWHAT FLATTER SOLN OFFERED BY THE 09/12Z
UKMET/CMC.  THE LATEST NAM SHARED THE SAME IDEA ABOUT TIMING OF
THE WAVE AS IT CROSSES THE GREAT LAKES ON DAY 2 AT 500 MB...BUT IT
REMAINED SOME 20 TO 40 METERS DEEPER THAN THE GFS AT H85 AND
CONSEQUENTLY HAD A STRONGER ADVECTION PATTERN AT LOW LEVELS.

THE ENSEMBLE CONSENSUS HAS NOT BEEN CONSISTENT FROM RUN TO
RUN...BUT CURRENT CLUSTERING STILL SUPPORTS PLACEMENT NEAR THE 00Z
GFS...JUST A BIT FLATTER AND FASTER. AS THE UPPER SYSTEM
APPROACHES THE NORTHEAST ON MON...THE GFS/ECMWF CONTINUE TO BE
REPRESENTATIVE OF A GOOD COMPROMISE.


CONTINUED ONSHORE FLOW INTO THE PACIFIC NORTHWEST FROM SUN-MON
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON ECMWF/ECMWF ENSEMBLE BLEND
CONFIDENCE: BELOW AVERAGE

FAST MOVING PACIFIC SYSTEMS IN A QUASI-ZONAL FLOW LOCATED JUST OFF
OF THE WEST COAST MAKE FOR A DIFFICULT FORECAST. AFTER THE
DEPARTURE OF THE SHORTWAVE REFERENCED ABOVE...CONTINUED ONSHORE
FLOW INTO THE PACIFIC NORTHWEST REMAINS WITH/AHEAD OF A POSSIBLE
CLOSED LOW WEST OF WASHINGTON BY MON. THERE WAS A DECIDED
ECMWF/ECMWF ENSEMBLE MEAN CAMP VS THE NON EC BASED CAMP.  AFTER
DISCUSSIONS WITH THE WPC MEDIUM RANGE FORECASTER...IT SEEMED THAT
THE ECMWF HAD BEEN STRUGGLING MORE THAN THE OTHER MODELS IN THIS
PART OF THE FLOW REGIME.  BLENDING IN SOME OF THE OTHER MODELS
WITH THE ECMWF ON DAY 3 WOULD YIELD AN UNREALISTICALLY EXPANSIVE
BUT WEAK SOLN.  AS A RESULT...WE OPTED TO RECOMMEND BLEND
EXCLUDING THE ECMWF OPNL/ENSEMBLES FOR THE TIME BEING.  THE BELOW
AVERAGE CONFIDENCE REFLECTS THE IDEA THAT THIS FLOW REGIME COULD
SUPPORT EITHER SOLN AND WHERE IT HAPPENS WOULD BE TIED TO A NEARLY
IMPOSSIBLE TO TIME SHORTWAVE THIS FAR OUT IN TIME.


...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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