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Model Diagnostics Discussion
 
(Caution: Version displayed is not the latest version. - Issued 0420Z Aug 29, 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
1220 AM EDT FRI AUG 29 2014

VALID AUG 29/0000 UTC THRU SEP 01/1200 UTC

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

==================================================
00Z NAM/GFS EVALUATION AND PRELIMINARY PREFERENCES
==================================================
NAM/GFS INITIALIZATION ERRORS DO NOT APPEAR TO
SIGNIFICANTLY AFFECT THEIR LARGE SCALE OUTPUT.
==================================================

...TROUGH PASSING THROUGH THE MIDWEST TOWARD THE NORTHEAST U.S...

PREFERENCE: BLEND OF THE OPERATIONAL MODELS...DROPPING THE NAM ON
DAY 3

THE GFS HAS WAFFLED A BIT ON FORWARD SPEED...BUT AFTER A
FAST-LOOKING 12Z RUN THE 18Z AND 00Z VERSIONS HAVE TRENDED BACK
TOWARD THE GLOBAL MODEL CONSENSUS. AS IN PAST RUNS...THE 00Z NAM
STRAYS TOWARD THE FAST END OF THE ENVELOPE BY THE END OF DAY
2...SUNDAY MORNING. IT IS ALSO WEAKER AT THAT TIME...AND WE SEE
ITS QPF FALL OFF COMPARED TO THE GLOBAL MODELS WHICH PRODUCE A
MORE SUBSTANTIAL SWATH OF PRECIPITATION OVER NORTHERN MAINE.


...BROAD LONGWAVE TROF ANCHORING THE WESTERN TO CENTRAL U.S. THIS
WEEKEND...

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

DURING THE WEEKEND...THE LONGWAVE PATTERN BEGINS TO FEATURE A
BROAD TROUGH EXTENDING FROM THE WEST COAST INTO THE CENTER OF
NORTH AMERICA...WITH 500 MB HEIGHTS DIPPING TWO STANDARD
DEVIATIONS BELOW CLIMATOLOGY OVER THE NORTHERN/CENTRAL ROCKIES. AS
NOTED IN EARLIER DISCUSSIONS...THE GEFS MEAN AND ECMWF ENSEMBLE
MEAN HAVE BEEN CONSISTENT FROM RUN TO RUN...AND THEY DEEPEN A
SURFACE TO 850 MB CYCLONE OVER NORTHERN MANITOBA BY MONDAY
MORNING. THIS CONSENSUS APPROACH FAVORS THE OPERATIONAL 12Z
ECMWF...BUT THERE IS NO REASON TO FULLY DISCOUNT SOLUTIONS SUCH AS
THE 12Z AND 00Z GFS...AND 12Z UKMET...WHICH PRODUCE A SLIGHTLY
DEEPER LEAD SHORTWAVE...AND WHICH TUG THE LOW LEVEL CYCLONE SOUTH
TOWARD THE U.S. BORDER ON DAY 3. THE 00Z NAM BECOMES MORE OF AN
OUTLIER...AS IT FEATURES A SIMILAR MID LEVEL WAVE AND LOW LEVEL
RESPONSE TAKING PLACE IN MINNESOTA AT 12Z ON SEPTEMBER 1ST.


...SHEAR AXIS AND EMBEDDED VORTICITY MAXIMA ORIGINATING NEAR THE
GULF COAST...

PREFERENCE: BLEND OF THE OPERATIONAL MODELS...EXCLUDING THE 12Z
CANADIAN

A SMALL MID LEVEL CIRCULATION IS FORECAST TO STALL ITS WESTWARD
DRIFT NEAR BROWNSVILLE TEXAS TODAY AND EVENTUALLY BECOME
STRETCHED...SHEARING OUT TOWARD THE NORTHEAST.
ANOTHER...SEPARATE...EASTERLY WAVE IS FORECAST TO DRIFT UP THROUGH
THE WESTERN GULF AND MOVE INTO THE LOWER MISSISSIPPI VALLEY BY
SATURDAY. THIS FEATURE WILL BE SQUEEZED BETWEEN A LARGE
SUB-TROPICAL RIDGE AND THE TROUGH PULLING OUT OF THE CENTRAL
U.S...YIELDING AN ACCELERATION OF THE FEATURE TOWARD THE NORTHEAST
U.S. THIS WILL LIKELY BE A PLAYER CONTRIBUTING TO RAIN AND SOME
HEAVY RAIN ALONG ITS PATH. MODEL SPREAD HAS DECREASED HERE...AND
THE 00Z NAM/GFS CLUSTER WELL WITH THE 12Z ECMWF/UKMET. THE 12Z
CANADIAN APPEARED TOO FAST.

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

BURKE