Prognostic Meteorological Discussion
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FXUS10 KWNH 281833
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
232 PM EDT THU AUG 28 2014

VALID AUG 28/1200 UTC THRU SEP 01/0000 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/GFS DEEMED SIGNIFICANT ENOUGH TO IMPACT THEIR FORECASTS.


...UPPER TROF CROSSING NORTHERN NEW ENGLAND THIS AFTERNOON...

FINAL PREFERENCE: GENERAL MODEL CONSENSUS
FORECAST CONFIDENCE: HIGH

AN UPPER TROF SEEN ON WATER VAPOR IMAGERY IS FORECAST TO CONTINUE
SLIDING EASTWARD WITH THE SYSTEM EXITING NORTHERN NEW ENGLAND
LATER TONIGHT. MODELS ARE IN CLOSE ENOUGH AGREEMENT TO SUPPORT A
GENERAL MODEL CONSENSUS.


...SLOW-MOVING UPPER LOW CROSSING THE CENTRAL PLAINS...
...EVENTUALLY MERGING WITH NORTHERN STREAM ENERGY...

FINAL PREFERENCE: BLEND OF THE 12Z GFS/ECMWF
FORECAST CONFIDENCE: AVERAGE

NUMEROUS SHOWERS AND THUNDERSTORMS CONTINUE TO FIRE AHEAD OF A
SLOW-MOVING UPPER CYCLONE WHICH IS CURRENTLY MOVING ACROSS THE
CENTRAL HIGH PLAINS. THROUGH FRIDAY EVENING...THE MODELS ARE IN
GOOD AGREEMENT WITH THE TIMING OF THE INITIAL UPPER LOW. MODEL
DIFFERENCES BEGIN TO EMERGE WITH THE TIMING OF THE NORTHERN STREAM
SYSTEM AND HOW QUICKLY THE TWO MERGE AS ONE. BY EARLY
SATURDAY...THE 12Z NAM/GFS WHICH WERE ON THE QUICKER SIDE PHASING
THE TWO HAVE BEEN JOINED BY THE 12Z CMC/ECMWF. MEANWHILE...THE 12Z
UKMET STILL DEPICTS A SEPARATE SHORTWAVE ADVANCING THROUGH THE
MIDDLE MS VALLEY SATURDAY MORNING. AS TIME PROGRESSES
FORWARD...THE 12Z NAM BECOMES QUICKER THAN THE CONSENSUS WHICH WAS
FORMED BY THE 12Z NAM/GFS/CMC/ECMWF. WPC WILL MAINTAIN THE
PREVIOUS PREFERENCE WITH CONFIDENCE SLIGHTLY RAISED AS THERE
REALLY IS ONLY ONE OUTLYING PIECE OF GUIDANCE NOW.


...SYSTEM LIFTING FROM THE GULF OF MEXICO INTO THE LOWER MS VALLEY
BY LATE FRIDAY...

FINAL PREFERENCE: BLEND OF THE 12Z GFS/ECMWF
FORECAST CONFIDENCE: SLIGHTLY ABOVE AVERAGE

EARLY IN THE PERIOD A MID-LEVEL IMPULSE WILL SETTLE ACROSS THE
WESTERN GULF COAST WHILE EVENTUALLY DRIFTING SOUTHWARD ALONG THE
COASTLINE. ALL OF THE MODELS SHOW THIS FEATURE QUITE WELL ALTHOUGH
THE 12Z NAM BECOMES VERY AGGRESSIVE IN BRINGING SEVERAL ADDITIONAL
SHORTWAVES INTO SOUTH TX. THIS ULTIMATELY LEADS TO VERY HEAVY
RAINFALL ON DAY 2. THE REMAINING MODELS SUGGEST THE FOCUS SHOULD
BE FARTHER UP THE COAST TOWARD THE TX/LA BORDER. MORE
SPECIFICALLY...THE 12Z GFS/ECMWF SHOW THE CORE OF THE ENERGY
CROSSING SOUTHWESTERN LA BY 30/1200Z. THE 12Z UKMET APPEARS TO
HAVE SHIFTED GEARS AND PUT MORE FOCUS ON THE SHORTWAVES CLOSER TO
THE MEXICAN BORDER. ON THE OTHER SIDE OF THE ENVELOPE IS THE 12Z
CMC WHICH IS QUICKER IN EJECTING THE SYSTEM INTO THE LOWER TN
VALLEY. WILL FAVOR THE AGREEMENT BETWEEN THE 12Z GFS/ECMWF WHILE
NOT INCLUDING THE 12Z UKMET THIS TIME AROUND.


...BROAD LONGWAVE TROF ANCHORING THE WESTERN TO CENTRAL U.S. THIS
WEEKEND...

FINAL PREFERENCE: BLEND OF THE 12Z ECMWF WITH THE 12Z GEFS/00Z
ECMWF ENSEMBLE MEANS
FORECAST CONFIDENCE: AVERAGE

DURING THE WEEKEND...THE LONGWAVE PATTERN BEGINS TO FEATURE A
BROAD TROF EXTENDING FROM THE WEST COAST INTO THE CENTER OF THE
COUNTRY WHILE POSITIVE HEIGHT ANOMALIES ANCHOR THE GREAT LAKES
DOWN INTO THE OH/TN VALLEYS. WHILE THE DETERMINISTIC MODELS VARY
IN THE PLACEMENT OF THIS TROF...THE 576-DM SPAGHETTI PLOTS SHOW
FAIRLY WELL CLUSTERED ENSEMBLE MEMBERS. WILL LEAN MORE HEAVILY ON
THE STRONGLY CLUSTERED 12Z GEFS/00Z ECMWF ENSEMBLE MEANS WHICH HAS
SUPPORT FROM THE 12Z ECMWF.


...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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