Prognostic Meteorological Discussion
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FXUS10 KWNH 291649
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1249 PM EDT FRI AUG 29 2014

VALID AUG 29/1200 UTC THRU SEP 02/0000 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 DEEMED SIGNIFICANT ENOUGH TO IMPACT ITS FORECAST.
MEANWHILE...THE 12Z GFS SEEMS TO SLIGHTLY UNDERPLAY THE MOISTURE
CONTENT ALONG THE WESTERN GULF COAST WITH VALUES OFF BY ABOUT 0.25
TO 0.35 INCHES.


...VORTICITY MAXIMA LIFTING THROUGH THE LOWER MS VALLEY ON
SATURDAY...

PRELIMINARY PREFERENCE: BLEND OF THE 12Z GFS WITH THE 00Z
ECMWF/UKMET
FORECAST CONFIDENCE: AVERAGE

A BROAD AREA OF DEEP CONVECTION OVER THE WESTERN GULF OF MEXICO IS
OCCURRING IN RESPONSE TO SEVERAL VORTICITY MAXIMA LIFTING
NORTHWARD TOWARD THE GULF COAST. THE ENERGY AND ASSOCIATED
ENHANCED MOISTURE CONTENT WILL EVENTUALLY WORK THEIR WAY INTO THE
LOWER MS VALLEY BY THIS EVENING. THE MYRIAD OF SHORTWAVES SHOULD
GRADUALLY CURL ALONG THE WESTERN EXTENT OF AN UPPER RIDGE
ANCHORING THE EAST COAST. THE 12Z NAM IS MORE AGGRESSIVE AT
KEEPING SOME ADDITIONAL ENERGY LOCKED AGAINST THE WESTERN GULF
COAST LATE SATURDAY. LOOKING AT OTHER MODELS...THE 00Z CMC IS
PROBABLY THE STRONGEST ALOFT AS IT CARRIES A COMPACT SHORTWAVE
THROUGH THE OH VALLEY ON SUNDAY MORNING WHILE THE 12Z GFS AND 00Z
ECMWF/UKMET ELONGATE THE ENERGY. THE LATTER THREE VARY A BIT IN
TIMING WITH THE 12Z GFS BEING QUICKER THAN THE 00Z ECMWF/UKMET.
WILL GO AHEAD AND FAVOR A MIX OF THESE AS THEY DO ALL SHOW A VERY
SIMILAR EVOLUTION.


....SHORTWAVE ENERGY MERGING WITH THE NORTHERN STREAM OVER THE
UPPER GREAT LAKES...

PRELIMINARY PREFERENCE: A NON-00Z CMC MODEL COMPROMISE
FORECAST CONFIDENCE: SLIGHTLY ABOVE AVERAGE

AN AREA OF HEIGHT FALLS ADVANCING THROUGH THE CENTRAL PLAINS WILL
EVENTUALLY WORK THEIR WAY INTO THE MIDDLE MS VALLEY/UPPER MIDWEST
WHERE A MERGER WITH THE NORTHERN STREAM WILL OCCUR. THROUGH
31/0000Z...THE MODELS ARE IN REASONABLE AGREEMENT WITH THE
EXCEPTION OF THE 00Z CMC WHICH IS A HAIR FASTER ACROSS THE GREAT
LAKES REGION. EVENTUALLY THIS DIFFERENCE GROWS IN TIME AS THE
SYSTEM BECOMES EMBEDDED IN THE FASTER SOUTHWESTERLY FLOW ALOFT.
WHILE THE 00Z ECMWF/UKMET GET A BIT AHEAD OF THE 12Z NAM/GFS WHILE
CROSSING NEW ENGLAND...IT APPEARS TO BE WITHIN THE GENERAL
ENVELOPE OF SPREAD SO WILL FAVOR A NON-00Z CMC MODEL COMPROMISE
HERE.


...LONGWAVE TROF SETTING FROM THE ROCKIES TO THE CENTER OF THE
COUNTRY...
...ADVANCING BAROCLINIC ZONE...

PRELIMINARY PREFERENCE: THROUGH 01/0000Z: GENERAL MODEL
COMPROMISE...THEREAFTER: BLEND OF THE 12Z GFS/06Z GEFS MEAN
FORECAST CONFIDENCE: INITIALLY ABOVE AVERAGE...THEN BECOMING
AVERAGE

OVER THE COURSE OF THE PERIOD...THE PATTERN WILL REALLY BEGIN TO
AMPLIFY ACROSS THE WESTERN TO CENTRAL U.S. THIS IS IN RESPONSE TO
HEIGHT FALLS MOVING INTO THE PACIFIC NORTHWEST WHICH EVENTUALLY
HELPS SHAPE A LONGWAVE TROF ACROSS MUCH OF THE NATIONS
MID-SECTION. THROUGH 60 HOURS/SUNDAY EVENING...THE MODELS HAVE A
DECENT GRASP ON THE EVOLVING SYNOPTIC PATTERN. THEREAFTER...THE
12Z NAM FAVORS DIGGING A SHORTWAVE A LITTLE MORE AGGRESSIVELY INTO
THE MIDDLE MS VALLEY. THE BIGGER DIFFERENCES BY DAY 3 ARE MORE
UPSTREAM ALONG THE WESTERN EXTENT OF THE LONGWAVE TROF. THE 00Z
ECMWF/ECMWF ENSEMBLE MEAN ARE MUCH MORE EMPHATIC ABOUT DIGGING
ENERGY INTO THE PACIFIC NORTHWEST BY MONDAY MORNING VERSUS OTHER
MODELS WHICH SHOW LESS AMPLITUDE. THIS IS WELL ILLUSTRATED BY THE
564-DM SPAGHETTI PLOT WITH A MAJORITY OF THE ECMWF ENSEMBLE
MEMBERS SHOWING THIS IDEA. NOT QUITE SOLD ON THIS SOLUTION YET SO
WILL AWAIT ADDITIONAL 12Z GUIDANCE. FOR NOW...A GENERAL MODEL
COMPROMISE IS RECOMMENDED THROUGH 60 HOURS BEFORE GOING TO MORE OF
A 12Z GFS/06Z GEFS MEAN BLEND.



...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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