Prognostic Meteorological Discussion
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FXUS10 KWNH 230449
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1249 AM EDT TUE SEP 23 2014

VALID SEP 23/0000 UTC THRU SEP 26/1200 UTC

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

...AN EVALUATION OF THE 12Z MODEL GUIDANCE ALONG WITH FINAL
PREFERENCES/FORECAST CONFIDENCE...

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

...NORTHERN STREAM TROF EXITING NEW ENGLAND ON TUESDAY...

PREFERENCE: GENERAL MODEL COMPROMISE
FORECAST CONFIDENCE: ABOVE AVERAGE

A NEUTRAL TO NEGATIVELY-TILTED TROF IS FORECAST TO CONTINUE
LIFTING NORTH AND EAST INTO TUESDAY WITH ADDITIONAL SHORTWAVES
TRACKING THROUGH UPPER NEW ENGLAND. ONLY SMALL DIFFERENCES ARE
NOTED AMONG THE AVAILABLE MODELS SO A GENERAL MODEL COMPROMISE
WOULD BE BEST SUITED WITH THIS SECTOR OF THE CONUS.

...UPPER LOW CUTTING OFF OVER THE CAROLINAS...
...INVERTED TROF ALONG THE EASTERN SEABOARD...

PREFERENCE: 22/12Z ECMWF OR 23/00Z NAM/GFS MORPHING TO 12Z ECMWF
ON DAY 3.
FORECAST CONFIDENCE: LOW

WATER VAPOR IMAGERY FROM LATE MONDAY AFTERNOON INTO MONDAY EVENING
SHOWED A POTENT SHORTWAVE DIVING INTO THE DEEP SOUTH WITH A WELL
DEFINED TONGUE OF DRY AIR SPILLING IN BEHIND IT...WITH INCREASING
AGREEMENT IN THE MODELS THAT THE SYSTEM WILL NEARLY STALL AS IT
BECOMES CUT OFF FROM THE NORTHERN STREAM. THE GENERAL CLUSTERING
IN THE GUIDANCE IS REASONABLE THROUGH TUESDAY EVENING/WEDNESDAY
MORNING BEFORE THE FORECAST BECOMES MORE NEBULOUS.  PREVIOUS RUNS
OF THE ECMWF HAD BEEN CONSISTENT IN KEEPING THE SHEAR AXIS TO THE
WEST...AND THE 23/00Z NAM AND GFS BOTH WENT THAT WAY.  WITH THE
SPREAD OF MODEL SOLNS INCREASING...FEEL THE ECMWF ENSEMBLE IS THE
BEST WAY TO.

...SLOW-MOVING UPPER TROF MOVING FROM THE CENTRAL GREAT BASIN TO
UPPER MIDWEST...

PREFERENCE: BLEND OF THE 00Z NCEP MODELS AND 22/12Z UKMET
FORECAST CONFIDENCE: AVERAGE

OVERALL THE MODELS PAINT A FAIRLY UNIFORM PICTURE OF THE TROF
MOVING FROM THE GREAT BASIN TO THE UPPER MIDWEST INTO WEDNESDAY.
BY WEDNESDAY EVENING...THOUGH...THE 00Z GFS GETS AHEAD OF THIS
CONSOLIDATED SOLUTION AND CONTINUES PUSHING THIS ENERGY EASTWARD
ALONG THE SOUTHERN FRINGE OF THE WESTERLIES. THE ENSEMBLES FROM
THE DAYTIME RUNS SUPPORTED STALLING THE SYSTEM AND ALLOWING
SHORTWAVE ENERGY TO SLOWLY MIGRATE SOUTHWARD. WPC WILL CONTINUE TO
FAVOR A COMBINATION OF THE 22/12Z UKMET AND THE 23/00Z NCEP RUNS
BUT NOT INCLUDE THE 22/12Z ECMWF THIS TIME GIVEN ITS MORE NORTHERN
DEPICTION.

...WEAK AXIS OF VORTICITY LINGERING OVER THE SOUTHERN HIGH
PLAINS...

PREFERENCE: GENERAL BLEND 12Z UKMET AND THE 00Z NCEP MODELS.
FORECAST CONFIDENCE: AVERAGE

MODELS CONTINUE TO ADVERTISE A WEAKNESS IN THE MID-LEVEL FLOW
ACROSS THE SOUTHERN/CENTRAL PLAINS BY WEDNESDAY/THURSDAY. SEE NO
REASON TO STRAY FROM PREVIOUS RATIONALE FOR FAVORING A SOLUTION
SIMILAR TO THE SYSTEM ACROSS THE NORTHERN TIER GIVEN BOTH BECOME
EMBEDDED IN SOME FORM OF GENERAL WEAKNESS ACROSS THE CENTER OF THE
COUNTRY BY THURSDAY.

...FULL-LATITUDE TROF ALONG THE IMMEDIATE WEST COAST BY THURSDAY...

PREFERENCE: BLEND OF THE 22/12Z GEFS AND 22/12Z ECMWF ENSEMBLE
MEANS
FORECAST CONFIDENCE: SLIGHTLY BELOW AVERAGE

THE PATTERN BECOMES QUITE AMPLIFIED ACROSS THE EASTERN PACIFIC AND
WESTERN U.S. WITH A RIDGE ANCHORING THE DESERT SOUTHWEST UP INTO
THE GREAT BASIN/ROCKIES. THE ENSEMBLE MEANS HAD FAIRLY GOOD
AGREEMENT AMONGST THEMSELVES AND CONTINUED TO HAVE THE SUPPORT OF
THE 22/12Z GEFS.

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

BANN

$$




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