Prognostic Meteorological Discussion
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FXUS10 KWNH 081909
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
209 PM EST THU DEC 08 2016

VALID DEC 08/1200 UTC THRU DEC 12/0000 UTC

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

...AN EVALUATION OF THE 12Z MODEL GUIDANCE ALONG WITH FINAL
PREFERENCES/FORECAST CONFIDENCE...


...DEEP UPPER TROUGH SWINGING THROUGH THE NORTHEASTERN U.S...
...ACCOMPANYING ARCTIC SURGE...

FINAL PREFERENCE: GENERAL MODEL COMPROMISE
FORECAST CONFIDENCE: ABOVE AVERAGE

WATER VAPOR IMAGERY AND SURFACE OBSERVATIONS SHOWED A BROAD
POSITIVELY-TILTED TROUGH MOVING THROUGH THE LOWER GREAT LAKES AND
OH RIVER VALLEY. THIS SYNOPTIC SYSTEM AND ITS ASSOCIATED POOL OF
ARCTIC AIR WILL CONTINUE TO MOVE TOWARD THE EASTERN SEABOARD
TODAY. ANY DISCERNIBLE DIFFERENCES OCCUR ONCE THE SYSTEM EXITS THE
U.S. WHICH WOULD SUPPORT A GENERAL MODEL COMPROMISE HERE.


...NEXT LOW AMPLITUDE WAVE CROSSING THE GREAT LAKES AND NEW
ENGLAND ON FRIDAY/SATURDAY...

FINAL PREFERENCE: NON-12Z CMC MODEL COMPROMISE
FORECAST CONFIDENCE: SLIGHTLY ABOVE AVERAGE

A SERIES OF SHORTWAVES CURRENTLY OVER SOUTH-CENTRAL CANADA SHOULD
MIGRATE EASTWARD FORMING A LOW-AMPLITUDE LONGWAVE TROUGH WHICH
WILL MOVE ACROSS THE GREAT LAKES BY FRIDAY/SATURDAY. THE PRIMARY
ISSUES EARLY ON HAD BEEN TIMING DIFFERENCES. BUT THIS APPEARS TO
HAVE BEEN RESOLVED AS THE 12Z ECMWF/UKMET MOVED EASTWARD JOINING
THE 12Z NAM/GFS. THUS...WILL RECOMMEND A NON-12Z CMC MODEL
COMPROMISE.


...POWERFUL CLOSED LOW OVER THE NORTHEAST PACIFIC BY 09/1800Z...
...PROGRESSIVE SHORTWAVE SWINGING THROUGH THE NORTHERN
PLAINS/UPPER MIDWEST...

FINAL PREFERENCE: BLEND OF THE 12Z ECMWF/00Z ECMWF ENSEMBLE MEAN
FORECAST CONFIDENCE: SLIGHTLY BELOW AVERAGE

WHILE INITIAL SHORTWAVE ENERGY MOVES THROUGH THE PACIFIC NORTHWEST
THIS MORNING...A MUCH MORE IMPRESSIVE UPPER LOW BEGINS TO APPROACH
VANCOUVER ISLAND BY 09/1800Z. AS THIS OCCURS...MODELS DEPICT A
PORTION OF THE CLOSED LOW WILL ACCELERATE EASTWARD AS AN OPEN WAVE
WITH THE 12Z NAM/GFS BEING MUCH MORE AMPLIFIED...PARTICULARLY THE
NAM. MOST OTHER SOLUTIONS FAVOR A MORE SUBTLE MID-LEVEL RESPONSE
AS THE SYSTEM NEARS THE NORTHERN HIGH PLAINS ON SATURDAY.
CONSIDERING THE 540-DM SPAGHETTI PLOT...MOST SOLUTIONS ARE QUITE
FLAT EXCEPT SOME OF THE GEFS MEMBERS. NOT CONFIDENT ENOUGH TO
CHOOSE AN AMPLIFIED DETERMINISTIC MODEL AT THIS TIME SO WILL LEAN
A COMBINATION OF THE 12Z ECMWF/00Z ECMWF ENSEMBLE MEAN TO STAY
MORE CONSERVATIVE.


...NEXT PACIFIC SYSTEM AFFECTING THE PACIFIC NORTHWEST BY SATURDAY
MORNING...
...EVENTUAL SHORTWAVE/SURFACE LOW CROSSING THE MIDDLE OF THE
CONUS...

FINAL PREFERENCE: BLEND OF THE 12Z GFS/ECMWF
FORECAST CONFIDENCE: SLIGHTLY BELOW AVERAGE

AS THE PARENT CLOSED LOW LINGERS BACK NEAR COASTAL WA...ADDITIONAL
JET ENERGY OFF THE PACIFIC BEGINS TO TAKE AIM AT THE NORTHWESTERN
U.S. THIS WEEKEND. ALL OF THIS PACIFIC SHORTWAVE ENERGY WILL SWING
INLAND CARVING OUT A MORE AMPLIFIED RESPONSE OVER THE CENTER OF
THE COUNTRY. ALL OF THE ENSEMBLE MEANS ARE QUITE FLAT WHICH MAKES
IT DIFFICULT TO UTILIZE ANY OF THESE GIVEN SOME AMPLIFICATION IN
THE FLOW IS EXPECTED. ENSEMBLE LOW PLOTS ARE QUITE MESSY WITH NO
DISTINCT CLUSTERS NOTED AS MEMBERS ARE GENERALLY SCATTERED ABOUT.
THE 12Z NAM/09Z SREF MEAN DO RESIDE WELL NORTH AND ARE QUICKER
THAN ANY AVAILABLE SOLUTION. OF COURSE THE EXACT PLACEMENT OF THE
SURFACE CYCLONES AND WEST-EAST FRONTAL BOUNDARY WILL PLAY A ROLE
IN WHERE OVERRUNNING PRECIPITATION WILL FALL. UNTIL THE GUIDANCE
BEGINS TO SHOW A BIT MORE CONSISTENCY...THE PLAN WILL BE TO
CONTINUE SPLITTING THE DIFFERENCE BETWEEN THE 12Z GFS/ECMWF.


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

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


RUBIN-OSTER



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