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Model Diagnostics Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1651Z Sep 20, 2014)
 
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Geographic Boundaries -  Map 1: Color  Black/White       Map 2: Color  Black/White


MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1251 PM EDT SAT SEP 20 2014

VALID SEP 20/1200 UTC THRU SEP 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.
==================================================

...EASTERN U.S...INCLUDING A COASTAL LOW...

PREFERENCE: BLEND OF 12Z NAM/GFS WITH 00Z ECMWF

MODELS ARE NOW SIMILAR IN HANDLING THE TRACK AND TIMING OF COASTAL
LOW PRESSURE AS IT PARALLELS THE ATALANTIC COAST BEFORE BEING
ABSORBED AHEAD OF A SYNOPTIC LOW/FRONT NEAR NEW ENGLAND. DAY 3
PRESENTS SOME INTERESTING QUESTIONS...THOUGH. THE 00Z CANADIAN
STOOD OUT AS A STRONG OUTLIER AMONG THE OPERATIONAL
MODELS...DEEPENING A BACKSIDE SHORTWAVE OVER THE
MID-ATLANTIC...AND PULLING THE OFFSHORE FRONTAL ZONE BACK TOWARD
THE SHORE. BUT THERE ACTUALLY WAS SOME SUPPORT FROM THE 00Z ECMWF
ENSEMBLE...IN WHICH 10 OF THE 50 MEMBERS PRODUCED A SIMILAR
SCENARIO...PREDICING A PRONOUNCED FRONTAL WAVE AND ASSOCIATED
PRECIPITATION AFFECTING THE MID ATLANTIC ON DAY 3. THE NUMBER OF
ECMWF AND CANADIAN ENSEMBLE MEMBERS DEPICTING THIS HAD INCREASED
OVER THE PAST FEW CYCLES. STILL...THE ENSEMBLE MAJORITY FAVORS
SOMETHING MORE PROGRESSIVE AND MUCH LESS PRONOUNCED IN THE LATTER
PART OF THE SHORT RANGE PERIOD. IT WOULD BE UNEXPECTED FOR A WAVE
OF SUCH LARGE SCALE AND ORGANIZATION TO FOLLOW IMMEDIATELY IN THE
WAKE OF THE BROAD CYCLONE TAKING SHAPE ON DAYS 1-2. WITH THE 12Z
NAM/GFS HOLDING THEIR COURSE...WE STILL FAVOR A NAM/GFS/ECMWF
BLEND...BUT ACKNOWLEDGE THAT CONFIDENCE FOR THE DAY 3 FORECAST HAS
BEEN REDUCED SOMEWHAT...AND WE WILL NEED TO WATCH THE TRENDS
CLOSELY.


...SHEAR AXIS TRAPPED IN THE UPPER RIDGE BUILDING OVER THE
SOUTHERN PLAINS...
 
PREFERENCE: BLEND OF THE OPERATIONAL MODELS

CONVECTIVE FLARE-UPS AND CONVECTIVELY INDUCED MID LEVEL
CIRCULATIONS HAD DIMINISHED IN BREADTH SINCE FRIDAY MORNING. THE
REMNANTS OF FORMER TROPICAL CYCLONE ODILE WERE...THEREFORE...SEEN
ONLY AS A WEAK 700 MB SHEAR AXIS...AND ONE THAT BECOMES LESS
PRONOUNCED WITH TIME. A RESIDUAL PLUME OF RICH MOISTURE WILL
CONTINUE TO SUPPORT PRECIPITATION...ESPECIALLY IN THE HIGH PLAINS
OF WEST TEXAS AND EASTERN NEW MEXICO. MODEL PRECIPITATION OUTPUT
IS SIMILAR ENOUGH TO RECOMMEND A CONSENSUS BLEND...BUT THE NAM MAY
BE TOO WET FARTHER EAST ACROSS TEXAS BY DAY 3...WHEN THE BUILDING
UPPER LEVEL RIDGE WILL TEND TO SUPPRESS ORGANIZED CONVECTION.


...SYSTEM TRACKING FROM CALIFORNIA TO THE NORTHERN PLAINS...
 
PREFERENCE: ANY OF THE OPERATIONAL MODELS

THE OPERATIONAL MODELS SHOW STRONG AGREEMENT AT THE SURFACE AND
ALOFT.


...DEEP TROUGH LEANING INTO THE PACIFIC NORTHWEST...

PREFERENCE: ANY OF THE OPERATIONAL MODELS...LESS WEIGHT ON THE 00Z
CANADIAN

A LEAD SHORTWAVE WILL BRING HEIGHT FALLS AND THE ONSET OF LIGHT
PRECIPITATION WEST OF THE WA/OR CASCADES ON MONDAY. THE WAVE WILL
PUSH A WEAK BOUNDARY INTO THE NORTHERN ROCKIES MON/TUE. A DEEPER
LONGWAVE TROUGH WILL APPROACH THE COAST BY LATE TUESDAY. MODEL
AGREEMENT IS STRONG...ASIDE FROM THE 00Z CANADIAN BEING SOMEWHAT
DEEPER AND WETTER WITH THE LEAD WAVE.

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

BURKE