Prognostic Meteorological Discussion
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000
FXUS10 KWNH 271645
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1244 PM EDT TUE SEP 27 2016

VALID SEP 27/1200 UTC THRU OCT 01/0000 UTC

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

...AN EVALUATION OF THE 12Z NAM/GFS ALONG WITH PRELIMINARY
PREFERENCES/FORECAST CONFIDENCE...


...BROAD UPPER LOW INITIALLY OVER THE GREAT LAKES REGION...
...EVENTUAL QUASI-STATIONARY LOW SITUATED ACROSS THE OH VALLEY
FROM 29/0000Z ONWARD...

PRELIMINARY PREFERENCE: BLEND OF THE 12Z GFS/00Z ECMWF
FORECAST CONFIDENCE: AVERAGE

WATER VAPOR IMAGERY AND SURFACE OBSERVATIONS DEPICTED A VERTICALLY
STACKED SYSTEM SPINNING JUST NORTH OF THE GREAT LAKES WITH A
FAIRLY WRAPPED UP OCCLUDED SYSTEM NOTED IN THE ANALYSIS. ALL
RECENT MODEL GUIDANCE INDICATE THIS NEGATIVE HEIGHT ANOMALY WILL
SINK SOUTHWARD EVENTUALLY BECOMING QUASI-STATIONARY OVER THE OH
RIVER VALLEY BY WEDNESDAY EVENING. THE 12Z NAM 500-MB HEIGHT
FORECAST SUGGESTS THIS SYSTEM WILL BE APPROXIMATELY 2 SIGMA BELOW
CLIMATOLOGY FOR LATE SEPTEMBER. GENERALLY SPEAKING...MODELS ARE IN
DECENT AGREEMENT WITH THE EVOLUTION OF THIS CYCLONE ALTHOUGH SOME
DIFFERENCES APPEAR BY 29/1200Z ONWARD. IN PARTICULAR...THE 09Z
SREF MEAN BECOMES A MORE EASTERN OUTLIER. BEYOND 30/0000Z...IT
APPEARS THE SYSTEM ACTUALLY RETROGRADES SOMEWHAT CARRYING THE
CLOSED LOW FROM EASTERN KY BACK TOWARD THE IN/OH BORDER.
OVERALL...MULTI-CYCLE ENSEMBLES DO SHOW A SLOWING TREND RELATIVE
TO PREVIOUS DAYS WHICH HAS BROUGHT THE HEAVY RAINFALL THREAT BACK
TOWARD THE I-95 CORRIDOR AND TOWARD THE TERRAIN. BY DAY 3...THE
GFS/ECMWF ENSEMBLES DIFFER A BIT WITH THE ECMWF MEMBERS BEING
SOUTHWEST OF THE GEFS. AT THIS POINT...THE BEST SOLUTION WOULD BE
TO SPLIT THE DIFFERENCE BETWEEN THE TWO.


...CLOSED LOW IN THE VICINITY OF THE GULF OF CA/SEA OF CORTEZ...
...EVOLVING SHORTWAVE LIFTING THROUGH THE NORTHERN ROCKIES ON
THURSDAY EVENING...

PRELIMINARY PREFERENCE: BLEND OF THE 12Z NAM/00Z ECMWF
FORECAST CONFIDENCE: SLIGHTLY ABOVE AVERAGE

THE BLOCKY MID-LATITUDE PATTERN IS EVIDENT BY THE MULTITUDE OF
CLOSED FEATURES ON THE MAP. FOR INSTANCE...ONE SUCH UPPER LOW IS
CURRENTLY SPINNING OVER THE NORTHERN GULF OF CA/SEA OF CORTEZ.
THIS SYSTEM IS FORECAST TO QUICKLY LIFT NORTHWARD WHILE BECOMING
MORE SHEARED IN NATURE. BY THURSDAY EVENING...THE 00Z CMC BECOMES
SLOWER WHILE THE 12Z GFS DEPICTS A MUCH MORE DAMPENED SOLUTION.
THIS ARTIFACT OF THE FORECAST PROCEEDS THROUGH FRIDAY. WILL PLAY
THE MORE DEFINED SHORTWAVE WHICH FOLLOWS THE 12Z NAM/00Z ECMWF
MORE CLOSELY.


...INITIAL COLD FRONT SWEEPING THROUGH THE UPPER INTERMOUNTAIN
WEST/NORTHERN ROCKIES EARLY ON...

PRELIMINARY PREFERENCE: GENERAL MODEL COMPROMISE
FORECAST CONFIDENCE: ABOVE AVERAGE

PROGRESSIVE HEIGHT FALLS LIFTING THROUGH WESTERN/CENTRAL CANADA
WILL STEER A COLD FRONT ACROSS THE UPPER INTERMOUNTAIN
WEST/NORTHERN ROCKIES EARLY IN THE PERIOD. THIS BOUNDARY QUICKLY
STALLS AS SURFACE WINDS TURN MORE EAST-SOUTHEASTERLY IN ADVANCE OF
THE NEXT UPPER TROUGH APPROACHING THE NORTHWESTERN U.S. COAST.
MODELS ARE CLOSE ENOUGH TO ONE ANOTHER TO AFFORD A GENERAL MODEL
COMPROMISE.


...DEEP UPPER TROUGH JUST OF THE PACIFIC NORTHWEST COAST BY
FRIDAY...

PRELIMINARY PREFERENCE: BLEND OF THE 06Z GEFS/00Z ECMWF ENSEMBLE
MEANS
FORECAST CONFIDENCE: AVERAGE

THE NEXT SYSTEM ON THE HORIZON EMERGES FROM THE NORTHEAST PACIFIC
WITH THESE HEIGHT FALLS GRADUALLY EXPANDING SOUTHWARD TOWARD THE
PACIFIC NORTHWEST COAST. ENSEMBLE SPAGHETTI PLOTS INDICATE MINIMAL
SPREAD WITH THIS SYSTEM ALTHOUGH THERE APPEAR TO BE RUN-TO-RUN
DIFFERENCES WHEN LOOKING AT THE DETERMINISTIC MODELS. FOR
EXAMPLE...THE 12Z GFS JUST TRENDED TOWARD THE SOUTH AND WEST
BRINGING IT AWAY FROM THE STRONGER ENSEMBLE SUPPORT. WILL AWAIT
FOR ADDITIONAL 12Z GUIDANCE BEFORE COMMITTING TO A MORE PRECISE
SOLUTION CHOICE. AS SUCH...THE PREFERENCE WILL BE A BLEND OF THE
06Z GEFS/00Z ECMWF ENSEMBLE MEANS.



...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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