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Model Diagnostics Discussion
 
(Latest Discussion - Issued 0647Z Aug 30, 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
247 AM EDT SAT AUG 30 2014

VALID AUG 30/0000 UTC THRU SEP 02/1200 UTC

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

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

....TROUGH SWEEPING ACROSS THE GREAT LAKES AND NORTHEAST...

PREFERENCE: BLEND OF THE 00Z OPERATIONAL MODELS...DROPPING THE NAM
ON DAY 3
CONFIDENCE: ABOVE AVERAGE

THE 00Z UKMET AND CANADIAN TRENDED IN SYNC WITH THE PREFERRED 00Z
GFS/ECMWF. THE 00Z NAM FITS WELL WITH THIS GROUP THROUGH DAY 2. IT
THEN DIFFERS IN HANDLING STREAM INTERACTION NEAR THE NEW ENGLAND
COAST...AND PRODUCES A MORE PRONOUNCED SHORTWAVE RIDGE EXTENDING
NORTHWARD INTO CANADA...RELATIVE TO THE GLOBAL MODEL CONSENSUS.


...SOUTHERN EXTENSION OF TROUGHING OVER THE EASTERN U.S...

PREFERENCE: BLEND OF 00Z GFS/ECMWF/UKMET
CONFIDENCE: AVERAGE

A POSITIVELY TILTED NORTHERN STREAM TROUGH AXIS DRAGGING TOWARD
THE MIDDLE MISSISSIPPI VALLEY WILL PHASE WITH AN EASTERLY WAVE
ROUNDING THE SUB-TROPICAL RIDGE TO YIELD A DEFINABLE SHORTWAVE
TROUGH THAT LIFTS THROUGH THE EASTERN U.S. THIS PERIOD. THE MODELS
SPREAD IS SMALL CONSIDERING THE DIFFICULTIES THAT ARISE IN
FORECASTING PHASING...ALONG WITH THE SLIGHT WARM CORE NATURE OF
THE EASTERLY WAVE. IN KEEPING WITH OUR PREFERENCE FROM THE 12Z
CYCLE...WE CONTINUE TO GIVE THE NOD TO THE GFS/ECMWF/UKMET. RUNS
OF THE CANADIAN HAVE TENDED TO BE ON THE FAST SIDE. THE 00Z NAM
PRODUCES LOWER HEIGHTS WITHIN THIS DEVELOPING WAVE AND WITH THE
SMALL VORTICITY MAXIMUM LEFT BEHIND IN SOUTH TEXAS. THIS IS A
COMMON TRAIT OF THE NAM AT THIS LATITUDE...BUT ITS FORECAST TIMING
AND EVOLUTION ARE OTHERWISE CLOSE TO CONSENSUS...SO THE OUTPUT MAY
STILL BE USEFUL.


...MEDIUM WAVELENGTH PACIFIC TROUGH REACHING THE MIDWEST BY
TUESDAY MORNING...

PREFERENCE: BLEND OF 00Z ECMWF/UKMET/CANADIAN
PREFERENCE: 00Z GFS GOOD EXCEPT DAY 3 WITH SPURIOUS MT/ND SHORTWAVE
CONFIDENCE: AVERAGE

A MODERATELY DEEP BUT PROGRESSIVE PACIFIC TROUGH WILL REACH THE
PLAINS BY MONDAY MORNING...WHILE LARGE SCALE LOW LEVEL
CYCLOGENESIS TAKES PLACE OVER CANADA BY THAT TIME. MODEL SPREAD IS
RELATIVELY LOW GIVEN THE LARGE SCALE OF THIS SYSTEM. THERE IS MORE
VARIABILITY WITH RESPECT TO A TRAILING SHORTWAVE TROUGH DIVING
INTO THE NORTHERN ROCKIES MONDAY...AND THE NEXT MEDIUM WAVELENGTH
TROUGH UPSTREAM IN THE PACIFIC. GENERALLY THE GLOBAL MODELS ARE
SIMILAR ENOUGH...AND FIT NEAR THE ENSEMBLE MEANS...TO BE BLENDED
AS A GROUP. THE 00Z GFS...IS QUICKER AND FARTHER NORTH WITH THE
INTERMEDIATE SHORTWAVE EMERGING FROM THE NORTHERN ROCKIES. THE
ECMWF IS FARTHER SOUTH AND ON THE DEEP SIDE OF THE SPREAD FOR THIS
SAME FEATURE...BUT IS GENERALLY CLOSER TO THE CONSENSUS THAN IS
THE GFS. THE NAM HAS TENDED TO ACT AS A DEEP OUTLIER WITH THE LEAD
WAVE AFTER DAY 1...AS IT PRODUCES LOW LEVEL CYCLOGENESIS SOUTH OF
THE U.S. BORDER...WHEREAS THE CONSISTENT ENSEMBLE SIGNAL IS FOR
THIS TO OCCUR WELL NORTH...BEGINNING IN MANITOBA.


...NEXT PACIFIC TROUGH REACHING THE NORTHWEST BY TUESDAY MORNING...

PREFERENCE: BLEND OF THE 00Z OPERATIONAL MODELS...EXCLUDING THE NAM
CONFIDENCE: AVERAGE

THE GFS HAS BEEN SOMEWHAT INCONSISTENT IN TIMING THIS SYSTEM
COMPARED TO THE CONSENSUS OVER THE PAST FEW CYCLES. THE ECMWF HAD
BEEN PREFERRED...AND REALLY DID NOT CHANGE IN THE 00Z RUN. THE
ECMWF ENSEMBLE MEAN HAS SUNK DOWN OR AMPLIFIED INTO A
CONFIGURATION FIRST PREDICTED BY THE OPERATIONAL MODEL. BUT THE
SPREAD IS NARROW ENOUGH...AND THE 00Z UKMET SHOWED MORE SUPPORT
FOR THE GFS...SUCH THAT WE ARE COMFORTABLE GROUPING THE GLOBAL
MODELS IN A CONSENSUS BLEND. THE NAM IS FLATTER WITH THIS
WAVE...AND THE GLOBAL MODELS PRODUCE WHAT LOOKS LIKE A MORE
REASONABLE SPACING OF MODERATELY PRONOUNCED MEDIUM WAVELENGTH
TROUGHS WITHIN THE BROAD TROUGH BEING CARVED OUT OVER CENTRAL
NORTH AMERICA.

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

BURKE