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Model Diagnostics Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1657Z Nov 20, 2014)
 
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Abbreviations and acronyms used in this product
 
Geographic Boundaries -  Map 1: Color  Black/White       Map 2: Color  Black/White


MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1157 AM EST THU NOV 20 2014

VALID NOV 20/1200 UTC THRU NOV 24/0000 UTC

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

==================================================
12Z NAM/GFS EVALUATION AND PRELIMINARY PREFERENCES
==================================================
NAM/GFS INITIALIZATION ERRORS DO NOT APPEAR TO
SIGNIFICANTLY AFFECT THEIR LARGE SCALE OUTPUT.
==================================================

...STRONG SOUTHERN STREAM TROUGH LEADING TO WIDESPREAD RAIN FROM
THE PLAINS EASTWARD...

PREFERENCE: BLEND OF 12Z GFS/00Z ECMWF

A DYNAMIC TROUGH OF SHORT TO MEDIUM WAVELENGTH WILL DIVE FROM
CALIFORNIA TOWARD THE RIO GRANDE BASIN. THE SYSTEM WILL CONTINUE
TO BE URGED ALONG TO THE EAST BY STRONG UPSTREAM FLOW...BUT THE
NAM/GFS HAVE TRENDED TOWARD A SLOWER PROGRESSION FROM LATE
SATURDAY INTO SUNDAY. THEY ARE ALSO A LITTLE DEEPER AND HAVE THE
TRACK SUPPRESSED SOUTHWARD COMPARED TO THE 00Z ECMWF. THESE TRENDS
APPEAR REASONABLE FOR A STRONG AND STILL DEEPENING WAVE. WHEN
COMBINED WITH THE 00Z UKMET/CANADIAN SOLUTIONS...THE 12Z RUNS
START TO MAKE THE ECMWF LOOK LIKE MORE OF AN OUTLIER...SO WE WOULD
EXPECT A GOOD CHANCE OF SEEING SIMILAR TRENDS IN THE NEW ECMWF RUN
WHEN IT ARRIVES. THE NAM IS WITHHELD FROM OUR PREFERENCE BECAUSE
IT IS LESS PREFERRED BY THE QPF DESKS...BUT ITS MASS FIELD
SOLUTION COULD BE USEFUL.


...NORTHERN STREAM TROUGH AFFECTING THE NORTHWEST/ROCKIES/NORTHERN
PLAINS...

PREFERENCE: BLEND OF 12Z NAM/GFS

THE NAM AND GFS TRENDED SLIGHTLY FASTER WITHIN THE NORTHERN STREAM
FLOW AFFECTING STATES FROM WA/OR EASTWARD TO THE DAKOTAS. NAM/GFS
TRENDS IN THE SOUTHERN STREAM APPEARED REASONABLE. STRONG WESTERLY
FLOW IN THE NORTHERN STREAM...ALONG WITH THE GEFS MEAN AND 00Z
UKMET/CANADIAN SOLUTIONS LEND SUPPORT TO THE NOTION OF A SLIGHTLY
FASTER SYSTEM. THE OLDER ECMWF AND ECMWF ENSEMBLE MEAN HAD
SUGGESTED SOMETHING A LITTLE SLOWER. THE GFS MAY ERR A BIT TOO FAR
ON THE FAST SIDE...WHICH WOULD BE CONSISTENT WITH ITS BIAS...BUT
ALL OF THIS SEEMS TO HAVE LESS OF AN IMPACT TO THE LOW LEVEL OR
SURFACE FORECAST. FOR NOW WE WILL SIDE WITH THE CONSENSUS AND THE
TRENDS.


...PHASING RESULTING IN A DEEP CYCLONE OVER THE MIDWEST AND GREAT
LAKES BY SUN/MON...

PREFERENCE: BLEND OF 12Z NAM/GFS

STREAM PHASING IS FORECAST TO YIELD THE BEGINNINGS OF A VERY DEEP
MIDWESTERN U.S. CYCLONE BY SUNDAY. OVER SEVERAL MODEL CYCLES THE
ENSEMBLE MEANS HAVE BEEN CONSISTENT IN THE PLACEMENT AND INTENSITY
OF THE SURFACE LOW. EVEN WITH THE SLIGHT MID LEVEL VARIATION IN
THE OPERATIONAL MODELS THEIR SURFACE FORECASTS HAVE NOT CHANGED
VERY DRAMATICALLY FROM RUN TO RUN. THE 12Z NAM/GFS SEEM TO CAPTURE
THE TRENDS...AND ARE PREFERRED...ALTHOUGH THE NAM IS LIKELY NOT
QUITE DEEP ENOUGH WITH THE SURFACE LOW...WHICH MOST GUIDANCE HAS
DROPPING BELOW 990 MB BY 24/00Z.


...NORTHEASTERN U.S...

PREFERENCE: ANY OF THE OPERATIONAL MODELS

A SHORTWAVE TROUGH WILL SWING THROUGH NEW ENGLAND BY
FRIDAY...FOLLOWED BY WARM ADVECTION AND A TRANSITION TOWARD MILD
AIR AND SOUTHWESTERLY FLOW ALOFT. THE MODELS HANDLE THIS SIMILARLY.

www.wpc.ncep.noaa.gov/html/model2.shtml...
www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml...

BURKE