Prognostic Meteorological Discussion
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000
FXUS10 KWNH 290652
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
251 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 MODEL EVALUATION AND 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
CONFIDENCE: ABOVE AVERAGE

THE 00Z GUIDANCE TRENDED SLIGHTLY FASTER IN FORWARD SPEED AND
TOWARD MORE RAPID DE-AMPLIFICATION OF THE UPPER TROUGH AS IT
PASSES THROUGH THE GREAT LAKES ON DAY 2. THE GFS WAS AN
EXCEPTION...AS IT TRENDED TOWARD THE EARLIER CONSENSUS...WITH A
SLIGHTLY SLOWER AND MORE PRONOUNCED SYSTEM. IN TERMS OF SENSIBLE
WEATHER AND LOCATION OF SURFACE BOUNDARIES...THE DIFFERENCE
BETWEEN THE GFS AND THE OTHER MODELS SEEMS MINIMAL ENOUGH TO LUMP
THEM TOGETHER. THE 00Z GLOBAL MODEL CONSENSUS DID TREND TOWARD THE
FASTER NAM...SO WE INCLUDE IT IN OUR PREFERENCE HERE...ALTHOUGH IT
MAY BE ON THE LIGHT SIDE WITH RESPECT TO DAY 3 QPF OVER NORTHERN
NEW ENGLAND.


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

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

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. RECENT GFS AND UKMET SOLUTIONS...HOWEVER...AND NOW THE
00Z ECMWF...PRODUCE A SLIGHTLY DEEPER LEAD SHORTWAVE WHICH TUGS
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 BY 12Z
ON SEPTEMBER 1ST. THE NAM IS ALSO OUT OF PHASE UPSTREAM OVER THE
PACIFIC NORTHWEST BY DAY 3...WHEREAS THE GLOBAL MODELS GENERALLY
AGREE TO THE SHORTWAVE SPACING WITHIN THE BROAD LONGWAVE TROUGH.


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

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

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 ALONG 30 DEGREES NORTH...AND THE TROUGH PULLING
OUT OF THE CENTRAL U.S. THIS SETUP YIELDS A NORTHEASTWARD
ACCELERATION OF THE DISTURBANCE...WHICH ITSELF MAY BECOME
CONVECTIVELY ENHANCED JUDGING BY THE MODELS. THIS WILL LIKELY BE A
PLAYER CONTRIBUTING TO RAIN AND SOME HEAVY RAIN ALONG ITS PATH
THROUGH THE EASTERN U.S. MODEL SPREAD HAS DECREASED HERE...BUT WE
DID CHOOSE TO UPDATE OUR PREFERENCE TO SELECT WHAT WE FEEL ARE THE
BEST SOLUTIONS. THE CANADIAN CONTINUES TO BE SLIGHTLY FAST. THE
GFS APPEARS TOO LIGHT WITH QPF ON DAY 3...AND THE NAM/SREF QPF
AXIS DRIFTS NORTH OF THE MULTI-CYCLE CONSENSUS FROM THE GLOBAL
MODELS. GIVEN THIS NORTHWARD BIAS IS A RECURRING FEATURE IN THE
NAM...WE PREFER THE ECMWF/UKMET.

...MODEL TREND GRAPHICS AT
www.wpc.ncep.noaa.gov/html/model2.shtml...
...500 MB FORECASTS AT
www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml...

BURKE
$$





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