Prognostic Meteorological Discussion
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FXUS10 KWNH 291848
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
247 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 CMC/UKMET/ECMWF ALONG WITH FINAL
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...

FINAL PREFERENCE: BLEND OF THE 12Z GFS/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 12Z/00Z CMC ARE
PROBABLY A LITTLE BIT STRONGER ALOFT AS THEY CARRY A COMPACT
SHORTWAVE THROUGH THE OH VALLEY ON SUNDAY MORNING WHILE THE 12Z
GFS/ECMWF/UKMET MORE OR LESS ELONGATE THE ENERGY. THE GROUPING OF
THE 12Z GFS/ECMWF/UKMET ARE MUCH BETTER CLUSTERED THAN EARLIER.
THE 12Z UKMET ENDS UP BEING A BIT WEST OF THE OTHER PAIR BUT THEY
ARE CLOSE ENOUGH TOGETHER TO FORM A REASONABLE BLEND.


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

FINAL PREFERENCE: BLEND OF THE 12Z NAM/GFS/ECMWF
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 12Z CMC WHICH IS A HAIR SLOWER ACROSS THE GREAT
LAKES REGION WHICH IS A COMPLETE REVERSAL OF ITS PREVIOUS RUN.
LATER ON...THE 12Z UKMET TENDS TO BECOME A BIT MORE PROGRESSIVE
WHICH LEAVES THE 12Z NAM/GFS/ECMWF MORE IN THE CENTER OF THE
SPREAD. WHILE THE 12Z NAM IS A BIT SLOWER THAN THE 12Z
GFS/ECMWF...IT APPEARS TO BE WITHIN THE ENVELOPE OF SPREAD. WPC
WILL FAVOR A BLEND OF THE 12Z NAM/GFS/ECMWF.


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

FINAL PREFERENCE: THROUGH 01/0000Z: GENERAL MODEL
COMPROMISE...THEREAFTER: BLEND OF THE 12Z GFS/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 12Z
ECMWF/00Z 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. STILL NOT SOLD ON THIS IDEA AS NO OTHER
MODEL HAS JOINED THIS SOLUTION. WILL MAINTAIN THE PREVIOUS
PREFERENCE FROM THE EARLIER ISSUANCE.


...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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