Prognostic Meteorological Discussion
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FXUS10 KWNH 311648
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1248 PM EDT SUN AUG 31 2014

VALID AUG 31/1200 UTC THRU SEP 04/0000 UTC

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

...AN EVALUATION OF THE 12Z NAM/GFS ALONG WITH PRELIMINARY
PREFERENCES/FORECAST CONFIDENCE...

THERE DID NOT APPEAR TO BE ANY INITIALIZATION ERRORS WITH THE 12Z
NAM/GFS DEEMED SIGNIFICANT ENOUGH TO IMPACT THEIR FORECASTS.


...AREA OF HEIGHT FALLS MOVING THROUGH THE LOWER GREAT
LAKES/NORTHEASTERN U.S...

PRELIMINARY PREFERENCE: GENERAL MODEL COMPROMISE
FORECAST CONFIDENCE: ABOVE AVERAGE

A PAIR OF SHORTWAVES MOVING THROUGH THE LOWER GREAT LAKES AND OH
VALLEY...RESPECTIVELY...WILL EVENTUALLY REACH THE NORTHEASTERN
U.S. BY LATER TONIGHT. THE FORMER WAVE SHOULD REMAIN MORE INTACT
RELATIVE TO THE OH VALLEY IMPULSE WHICH WILL BE A LITTLE MORE
SHEARED IN NATURE. GIVEN THE LIMITED TIME THIS SYSTEM AFFECTS THE
CONUS...THE MODELS ARE IN CLOSE ENOUGH AGREEMENT TO AFFORD A
GENERAL MODEL COMPROMISE HERE.


...LONGWAVE TROF EXTENDING FROM THE ROCKIES THROUGH THE GREAT
LAKES...
...PROGRESSIVE COLD FRONT...

PRELIMINARY PREFERENCE: BLEND OF THE 12Z NAM/00Z ECMWF
FORECAST CONFIDENCE: ABOVE AVERAGE

WATER VAPOR IMAGERY SHOWED A LONGWAVE TROF INITIALLY SPANNING MUCH
OF THE WESTERN TO CENTRAL U.S. WITH SEVERAL EMBEDDED SHORTWAVES
RACING TOWARD THE NORTH AND EAST. THE LEAD ENERGY AND ITS
ACCOMPANYING SPEED MAX TRACKING TOWARD THE MIDDLE MS VALLEY WILL
CARRY AN INHERENT HEAVY RAINFALL AND SEVERE WEATHER THREAT. EARLY
ON...THE 12Z GFS APPEARS A TAD QUICKER ALOFT AND AT THE SURFACE
WITH THE BAROCLINIC ZONE. OTHER MODELS APPEAR TOLERABLE WITHIN THE
GENERAL NOISE THROUGH MONDAY WITH THIS SHORTWAVE. AS THIS SYSTEM
LIFTS ACROSS THE CANADIAN BORDER ADDITIONAL LONGWAVE ENERGY WILL
FILL IN ACROSS THE CENTRAL U.S. THE 12Z NCEP GUIDANCE ARE A SMIDGE
QUICKER RELATIVE TO THE 00Z ECMWF/CMC/UKMET WITH THIS ASPECT OF
THE TROF. AT THE SURFACE...THE ENSEMBLE MEANS ALL ARE FAIRLY CLOSE
TO ANOTHER THROUGH 02/0000Z WITH THE POSITION OF THE FRONT AND
AREA OF LOW PRESSURE OVER ONTARIO. ALL AND ALL...THE ENSEMBLE
MEANS OFFER A GREAT HANDLE ON THE PATTERN WITH THE 12Z NAM/00Z
ECMWF FOLLOWING SUIT WITH THE MEANS QUITE WELL. THE RECOMMENDATION
WILL BE A BLEND OF THE 12Z NAM/00Z ECMWF.


...AMPLIFIED SHORTWAVE REACHING THE PACIFIC NORTHWEST BY TUESDAY
AFTERNOON...

PRELIMINARY PREFERENCE: BLEND OF THE 12Z GFS/00Z ECMWF
FORECAST CONFIDENCE: SLIGHTLY BELOW AVERAGE

AS THE LONGWAVE TROF BEGINS TO EJECT EASTWARD...ADDITIONAL
SHORTWAVE ENERGY IS FORECAST TO DROP DOWN FROM THE NORTHEAST
PACIFIC AND BRING AN AMPLIFIED SYSTEM INTO THE PACIFIC NORTHWEST
BY TUESDAY AFTERNOON. BY MID-WEEK THE 12Z NAM LOOKS TOO SLOW AND
IS WEST OF THE ENSEMBLE MEANS INCLUDING THE 09Z SREF MEAN. THE
564-DM SPAGHETTI PLOT SHOWS AGREEMENT THAT A POSITIVELY-TILTED
TROF WILL BE LOCATED OVER THE NORTHERN GREAT BASIN/ROCKIES WITH
SOME SPREAD REGARDING TIMING AND HOW MUCH ENERGY HANGS BACK TOWARD
THE SOUTHWEST. THE 00Z ECMWF ENSEMBLE MEMBERS SHOW SOMETHING A
LITTLE SLOWER THAN THE MORE EASTWARD 00Z GEFS MEMBERS/09Z SREF
MEAN. FOR NOW WILL SPLIT THE DIFFERENCE BETWEEN THE TWO CAMPS
UNTIL NEW GUIDANCE ARRIVES. THE 12Z GFS/00Z ECMWF REPRESENTS THIS
TIMING DIFFERENCE WELL ENOUGH TO AFFORD IN THE PREFERENCE.


...PAIR OF EASTERLY WAVES AFFECTING EASTERN MEXICO AND
FL...RESPECTIVELY...

PRELIMINARY PREFERENCE: EASTERN MEXICO WAVE: NON-12Z NAM MODEL
COMPROMISE...FL WAVE: NON-12Z NAM/00Z UKMET MODEL COMPROMISE
FORECAST CONFIDENCE: AVERAGE

TWO EASTERLY WAVES ARE FORECAST TO AFFECT THE BAY OF CAMPECHE AND
THE BAHAMAS...RESPECTIVELY. WITH REGARD TO THE SYSTEM APPROACHING
EASTERN MEXICO...THE 12Z NAM IS DEFINITELY THE MOST NORTHERN
SOLUTION WHICH WOULD BRING HEAVY RAINFALL INTO SOUTH TX ON DAY 3.
THE OTHER MODELS ARE CLOSE ENOUGH WITH THEIR MORE SOUTHERN
POSITIONS WITH LESS IMPACTS ACROSS THE LOWER 48. MEANWHILE...WITH
THE EASTERLY WAVE CROSSING THE BAHAMAS...THE 12Z NAM WAS QUICKER
BEING OFF TOWARD THE WEST WHILE THE 00Z UKMET DEPICTS A MORE
SUPPRESSED SOLUTION. THE 12Z GFS AND 00Z ECMWF/CMC LEAN FAVORABLY
TOWARD CLUSTERED ENSEMBLE MEANS SO A NON-12Z NAM/00Z UKMET
PREFERENCE IS RECOMMENDED.


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

RUBIN-OSTER

$$





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