Prognostic Meteorological Discussion
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000
FXUS10 KWNH 211845
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
244 PM EDT SUN SEP 21 2014

VALID SEP 21/1200 UTC THRU SEP 25/0000 UTC

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

==============================================
12Z MODEL EVALUATION AND PREFERENCES
==============================================
NAM/GFS INITIALIZATION ERRORS DO NOT APPEAR TO
SIGNIFICANTLY AFFECT THEIR LARGE SCALE OUTPUT.
==============================================

...EASTERN U.S THROUGH MONDAY...

PREFERENCE: ANY OF THE OPERATIONAL MODELS
CONFIDENCE: ABOVE AVERAGE

A WELL DEFINED CYCLONE WILL PUSH EAST FROM NEW ENGLAND...ABSORBING
A COASTAL LOW LIFTING UP FROM THE CAROLINAS. MODEL SPREAD IS
MINIMAL. THE ECMWF IMPROVED UPON ITS SURFACE SOLUTION WITH RESPECT
TO THE COASTAL LOW.


...EASTERN U.S TUE/WED...

PREFERENCE: 00Z ECMWF ENSEMBLE MEAN...WITH GROWING SUPPORT
CONFIDENCE: AVERAGE

LARGE MODEL SPREAD LEADS TO AVERAGE OR SLIGHTLY BELOW AVERAGE
CONFIDENCE AND LEADS US TO PREFER AN ENSEMBLE MEAN OVER THE
SOUTHEAST U.S. BY TUE/WED. THE SYNOPTIC PATTERN ALLOWS FOR
DEVELOPMENT OF A BROAD UPPER LOW AS SEEN IN RECENT ECMWF RUNS...AS
THE NORTHERN STREAM AMPLIFIES FROM COAST TO COAST...AND SHORTWAVE
ENERGY DESCENDS TOWARD A WEAKNESS BETWEEN TWO RIDGES OVER THE
SOUTHEAST UNITED STATES AND THE NORTHERN GULF OF MEXICO. A
MODERATELY STRONG CLUSTER OF 00Z ECMWF ENSEMBLE MEMBERS SUPPORTS
THIS NOTION. ALTHOUGH THE PLACEMENT OF THEIR SOLUTIONS IS
SCATTERED...THE 12Z OPERATIONAL MODELS...ALL EXCEPT THE GFS...LENT
MORE SUPPORT...BY TRENDING TOWARD A CLOSED MID LEVEL CIRCULATION
BY 25/00Z. THE GFS/GEFS HAVE SHOWN ALMOST NO SUPPORT TO THE IDEA
OVER THE PAST FEW CYCLES...BUT THE GROWING NUMBER OF MODELING
SYSTEMS SHOWING THIS PLAUSIBLE SCENARIO GIVES US A LITTLE GREATER
CONFIDENCE. IN ANY CASE...THIS WILL OR WILL NOT OCCUR ON THE HEELS
OF A LARGE SCALE TROUGH...INITIALLY ATOP STABLE AIR...SO THE VERY
AGGRESSIVE QPF SOLUTIONS FROM THE 00Z ECMWF/UKMET MAY HAVE BEEN
TOO OPTIMISTIC AT PULLING MOISTURE INLAND. THE BEST COMPROMISE
SEEMS TO BE THE ECMWF ENSEMBLE MEAN...WHOSE QPF IS MORE SIMILAR TO
THE LATEST 12Z ECMWF/UKMET/CANADIAN. SOME MODERATE RAINS ARE
FORECAST ALONG THE COASTS OF GA/SC/NC ON WEDNESDAY...AND LIGHTER
RAIN INLAND 100 MILES OR MORE. THE MODEL PREFERENCE HERE WAS
COORDINATED WITH WPC MEDIUM RANGE AND DAY 2/3 QPF DESKS. PLEASE
SEE THEIR DISCUSSIONS FOR DETAILS.


...SHEAR AXIS TRAPPED IN THE UPPER RIDGE BUILDING OVER THE
SOUTHERN PLAINS...

PREFERENCE: BLEND OF THE OPERATIONAL MODELS
CONFIDENCE: AVERAGE

DATING BACK OVER THE PAST SEVERAL CYCLES THE MODELS...BEYOND THE
FIRST 12 HOURS OF THE FORECAST...HAVE STRUGGLED TO MAINTAIN
DEFINITION OF A 850-700 MB SHEAR AXIS TRAPPED BENEATH A
STRENGTHENING UPPER LEVEL RIDGE. CONVECTIVE FLARE-UPS WITHIN A
PSEUDO-TROPICAL AIRMASS CONTINUE TO DRIVE A HEAVY RAIN THREAT OVER
PARTS OF TX/NM. THIS ACTIVITY MAY GRADUALLY LIFT AND REFORM NORTH
AND EAST TOWARD THE TX PANHANDLE AND ADJACENT PARTS OF OK THROUGH
TUE/WED. THE MODEL SOLUTIONS ARE SIMILAR BUT CONFIDENCE REGARDING
DETAILS OF THE CONVECTIVE FORECAST IS DIMINISHED AT LONGER LEAD
TIMES OWING TO CONTINUED SMALL SCALE FEEDBACK BEING OBSERVED AND
NOT OFTEN APPEARING IN THE MODELS.


...SYSTEM TRACKING FROM THE GREAT BASIN INTO THE PLAINS...

PREFERENCE: BLEND OF 12Z GFS/ECMWF/UKMET
CONFIDENCE: AVERAGE

THERE HAS BEEN A TREND FOR THE MODELS TO SLOW THIS SYSTEM AND
DEPICT A SOMEWHAT MORE PRONOUNCED CIRCULATION BY THE TIME IT PULLS
INTO THE CENTRAL PLAINS. RECENT GFS RUNS...ESPECIALLY THE 06Z/12Z
RUNS...FIT BEST WITH THE ENSEMBLE TRENDS. THE 12Z UKMET AND
CANADIAN ALSO LEND SUPPORT. THE 00Z AND 12Z ECMWF RUNS ARE PERHAPS
IN THE LEAST AMOUNT OF AGREEMENT...AS THEY ARE WEAKER AND FASTER
BY DAY 3. THE 12Z NAM TRENDED EVEN SLOWER THAN THE
GFS/UKMET/CANADIAN CLUSTER...AND ALSO CLOSED THE CIRCULATION
FARTHER SOUTH INTO KS/NE. WE PREFER THE GFS-LED SOLUTIONS IN WHICH
THE CLOSED LOW ENDS UP NEAR NE/IA BY 25/00Z...WHICH IS MORE
CONSISTENT WITH THE EJECTION OF THIS SYSTEM FROM NORTHEAST WYOMING
ON DAY 2.


...DEEP TROUGH WITH INCREASING IMPACT TO THE PACIFIC NORTHWEST...

PREFERENCE: BLEND OF THE 12Z OPERATIONAL MODELS...LESS WEIGHT ON
THE NAM
CONFIDENCE: ABOVE AVERAGE

THIS TROUGH WILL BEING TO PRODUCE MORE MEANINGFUL IMPACTS AND
WIDESPREAD RAIN BY WEDNESDAY. MODEL SPREAD IS MINIMAL...BUT THE
12Z NAM BECOMES MORE AMPLIFIED THAN CONSENSUS BY 25/00Z.

...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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