Prognostic Meteorological Discussion
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000
FXUS10 KWNH 010443
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1242 AM EDT MON SEP 01 2014

VALID SEP 01/0000 UTC THRU SEP 04/1200 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 SLIDING FROM THE MIDWEST TO THE NORTHEAST BEGINNING
TODAY...

PREFERENCE: BLEND OF THE OPERATIONAL MODELS

THIS TROUGH CONSISTS OF A LEAD SHORTWAVE AND A SMALLER SHORTWAVE
THAT QUICKLY FOLLOWS. THE MODELS ARE REMARKABLY SIMILAR...PROBABLY
RELATED TO THE LONGER WAVELENGTH AND CLASSIC BEHAVIOR OF THE
LARGER SCALE TROUGH CARVED OUT BY THESE SHORTWAVES. THE SYSTEM
WILL DRAG A COLD FRONT THROUGH THE NORTHERN AND NORTHEASTERN
U.S...WHILE THE TAIL END STALLS IN THE MID MISSISSIPPI VALLEY AND
CENTRAL PLAINS.


...PACIFIC TROUGH AFFECTING THE WEST AND SPILLING INTO THE
NORTHERN PLAINS LATE WED...
...UPPER LEVEL SHORTWAVE ABSORBED OVER THE SOUTHWEST...

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

THE ECMWF/CANADIAN HAVE BEEN CONSISTENT IN FORECASTING THE DEPTH
AND PROGRESSION OF THIS TROUGH OVER THE PAST FEW DAYS. THEY SHARE
STRONG SUPPORT FROM THE ECMWF ENSEMBLE. THE GFS HAS BEEN MORE
VARIABLE. IT IS DIFFICULT TO SAY THAT THE GFS IS INCORRECT...BUT
IT AND THE ASSOCIATED GEFS MEAN HAVE BEEN TRENDING TOWARD LESS
AMPLITUDE AND QUICKER PROGRESSION. GIVEN THAT SHORTWAVE RIDGING IS
DEVELOPING NORTH OF THIS FEATURE...AS PART OF A DEVELOPING SPLIT
FLOW IN WESTERN CANADA...WE STILL FAVOR THE DEEPER SOLUTIONS
WITHIN THE TROUGH OVER THE WESTERN U.S.

MEANWHILE...ALL THE MODELS FORECAST A WEAK SHEAR AXIS OR CYCLONIC
CIRCULATION OFF OF CALIFORNIA TO BECOME ABSORBED INTO THE
DEEPENING NORTHERN STREAM FLOW...AND COME INTO THE DESERT
SOUTHWEST BY DAY 3.


...PAIR OF EASTERLY WAVES NEARING SOUTH TEXAS AND
FLORIDA...RESPECTIVELY...

PREFERENCE: BLEND OF THE OPERATIONAL MODELS

THE NATIONAL HURRICANE CENTER PLACES A 50 PERCENT CHANCE OF
TROPICAL CYCLONE FORMATION IN THE NEXT 2 DAYS...ON AN EASTERLY
WAVE THAT WAS CROSSING THE YUCATAN EARLY MONDAY MORNING. THE MODEL
SPREAD HAS NARROWED SINCE THE 31/00Z CYCLE. THE NAM PRODUCES A
SLOWER INTENSIFICATION OF THIS WARM CORE SYSTEM...WHILE THE GLOBAL
MODELS ARE TRENDING HEAVIER IN THEIR QPF...MORE LIKE THE NAM.
THOUGH THE CENTER OF ANY POTENTIAL CIRCULATION IS MORE LIKELY TO
AFFECT MEXICO...SOME PRECIPITATION IS LIKELY TO AFFECT SOUTH
TEXAS...AND THERE ARE NO PARTICULAR OUTLIERS AMONG THE OPERATIONAL
MODELS.

A SEPARATE WAVE APPROACHING THROUGH THE BAHAMAS INTO FLORIDA ON
DAYS 2/3...SHOWS LITTLE VARIATION IN THE MODELS. THE NAM IS
CHARACTERISTICALLY LARGE IN THE EXPANSE OF DEPRESSED HEIGHTS IT
PREDICTS AROUND THE FEATURE...BUT ITS WIND FIELDS AT VARIOUS
LEVELS ARE NOT FAR OFF FROM THE GLOBAL MODEL CONSENSUS.

...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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