Prognostic Meteorological Discussion
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000
FXUS10 KWNH 010653
PMDHMD

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

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. THE ONLY NOTABLE MODEL DIFFERENCE IS A SLIGHT
HICCUP IN THE NAM EARLY ON...TODAY AND TONIGHT...WHEN IT IS SLOW
TO VEER WINDS WITH THE FRONTAL PASSAGE THROUGH THE MID MISSISSIPPI
VALLEY. IT LATER CATCHES UP TO CONSENSUS.


...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/ECMWF
CONFIDENCE: AVERAGE

THE ECMWF/CANADIAN HAD BEEN CONSISTENT IN FORECASTING THE DEPTH
AND PROGRESSION OF THIS TROUGH OVER THE PAST FEW DAYS. THEY SHARED
STRONG SUPPORT FROM THE ECMWF ENSEMBLE. THE 00Z ECMWF MAINTAINED
CONTINUITY...BUT THE CANADIAN SHOWS A MUCH FASTER LEAD WAVE
THROUGH THE DAKOTAS...EVEN FASTER THAN THE UKMET RUNS WHICH HAVE
BEEN VERY DEEP BUT ALSO FAST WITH THIS LEAD WAVE. 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...WHILE NOT AS
AGGRESSIVE AS THE MOST RECENT UKMET/CANADIAN SOLUTIONS. 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...MORE
LIKE THE 00Z NAM AND ECMWF. THE DEPTH OF THE NAM AT SURFACE AND
ALOFT MAY BE A LITTLE SPURIOUS OVER SOUTHERN SASKATCHEWAN BY
THURSDAY MORNING...BUT FOR THAT PORTION OF THE SYSTEM AFFECTING
THE U.S. WE SEE GOOD AGREEMENT BETWEEN THE NAM/ECMWF.

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.


...EASTERLY WAVE NEARING SOUTH TEXAS...

PREFERENCE: BLEND OF THE OPERATIONAL MODELS
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

WITH AN EASTERLY WAVE THAT WAS CROSSING THE YUCATAN EARLY MONDAY
MORNING...THE NATIONAL HURRICANE CENTER FORECASTS A 60 PERCENT
CHANCE OF TROPICAL CYCLONE FORMATION IN THE NEXT 2 DAYS. THE MODEL
SPREAD HAS NARROWED SINCE THE 31/00Z CYCLE. THOUGH THE CENTER OF
ANY POTENTIAL CYCLONE IS MORE LIKELY TO AFFECT MEXICO...THE OUTER
REACHES OF PRECIPITATION...AND A GENERALLY MOIST ONSHORE
FLOW...ARE LIKELY TO AFFECT SOUTH TEXAS. THERE ARE NO OUTLIERS
AMONG THE OPERATIONAL MODELS.


...EASTERLY WAVE NEARING FLORIDA...

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

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. THE 00Z
UKMET WAS SOMEWHAT LESS IN SYNC WITH THE CONSENSUS ALOFT...WHERE
IT LOSES DEFINITION OF THE TROUGH AT THE LATITUDE OF SOUTH
FLORIDA...AND EMPHASIZES LOCAL INTENSIFICATION OF VORTICITY BOTH
TO THE NORTH AND SOUTH ALONG THE INVERTED TROUGH AXIS AT DIFFERENT
TIMES.

...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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