Prognostic Meteorological Discussion
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000
FXUS10 KWNH 300453
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1252 AM EDT SUN AUG 30 2015

VALID AUG 30/0000 UTC THRU SEP 02/1200 UTC

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

...AN EVALUATION OF THE 00Z NAM/GFS ALONG WITH PRELIMINARY
PREFERENCES/FORECAST CONFIDENCE...

THERE DID NOT APPEAR TO BE ANY INITIALIZATION ERRORS WITH THE 00Z
NAM/GFS DEEMED SIGNIFICANT ENOUGH TO IMPACT THEIR FORECASTS.


...SHORTWAVE/ASSOCIATED FRONTAL ZONE SKIRTING UPPER NEW ENGLAND
EARLY MONDAY...

PRELIMINARY PREFERENCE: A NON-12Z UKMET MODEL COMPROMISE
FORECAST CONFIDENCE: SLIGHTLY ABOVE AVERAGE

THE UPPER FLOW GRADUALLY BEGINS TO AMPLIFY OVER EASTERN CANADA BY
EARLY NEXT WEEK. MODELS EXHIBIT SOME VARIATION IN TIMING ALTHOUGH
THE BIGGER DIFFERENCE IS WITH REGARD TO THE AMPLITUDE. THE 12Z
UKMET SHOWS MORE AMPLIFICATION SO THIS WILL BE DISMISSED IN FAVOR
A COMPROMISE OF THE OTHER AVAILABLE SOLUTIONS.


...LOBE OF VORTICITY LIFTING FROM THE CENTRAL GULF COAST UP TOWARD
THE LOWER MID-ATLANTIC...
...RETROGRADING UPPER LOW MOVING TOWARD THE SOUTHERN PLAINS...

PRELIMINARY PREFERENCE: FIRST SYSTEM: MODEL COMPROMISE BETWEEN THE
00Z NAM/GFS AND 12Z ECMWF...SECOND SYSTEM: A NON-12Z CMC MODEL
COMPROMISE
FORECAST CONFIDENCE: AVERAGE

WATER VAPOR IMAGERY TONIGHT SHOWS A POTENT UPPER LOW CROSSING INTO
EXTREME SOUTHERN AL WITH ABUNDANT CONVECTION OCCURRING WELL TO ITS
EAST ALONG AN ENHANCED PLUME OF MOISTURE. THERE IS A GENERAL
CONSENSUS THAT THE SYSTEM WILL LIFT NORTH AND EAST TOWARD THE
MID-ATLANTIC DURING THE NEXT 24 TO 36 HOURS. THE 00Z NAM/GFS AND
12Z ECMWF ARE IN NEAR ALIGNMENT WHILE THE 12Z CMC/UKMET APPEAR TO
BE AFFECTED WITH HOW THEY HANDLE THE REMNANTS OF ERIKA. WILL STAY
AWAY FROM THESE LATTER SOLUTIONS. THE PREFERENCE WILL BE A
COMPROMISE BETWEEN THE 00Z NAM/GFS AND 12Z ECMWF.

MEANWHILE...TO THE WEST...A SEPARATE WEAKNESS IN THE FLOW WILL
AFFECT THE SOUTHERN PLAINS/LOWER MS VALLEY. THROUGH
31/1800Z...THERE IS DECENT AGREEMENT WITH A PAIR OF REGIONS OF
CYCLONIC FLOW...ONE OVER SOUTH TX WHILE THE OTHER SITS OVER THE
OZARKS. DIFFERENCES DURING THE PERIOD ARE NOT AS SIGNIFICANT AS
PREVIOUS DAYS...BUT THE 12Z CMC DOES TEND TO DRAG SOME OF THE
VORTICITY FARTHER EAST THAN OTHER SOLUTIONS. THUS...WILL LEAN ON A
NON-12Z CMC MODEL COMPROMISE WITH THIS ARRAY OF SYSTEMS.


...PERSISTENT UPPER TROUGH ACROSS THE NORTHWESTERN U.S...

PRELIMINARY PREFERENCE: BLEND OF THE 00Z GFS/12Z ECMWF WITH THE
12Z ECMWF ENSEMBLE MEAN
FORECAST CONFIDENCE: SLIGHTLY BELOW AVERAGE

A SERIES OF IMPRESSIVE SHORTWAVES TRACKING THROUGH THE PACIFIC
NORTHWEST AND ADJACENT LOCATIONS DOWNSTREAM WILL HELP MAINTAIN A
PERSISTENT/ANOMALOUS LONGWAVE TROUGH ACROSS THE REGION THROUGH THE
MIDDLE OF NEXT WEEK. THE 12Z UKMET IS SLOWER EJECTING A SHORTWAVE
TOWARD SOUTHERN SASKATCHEWAN WHILE DIFFERENCES CONTINUE TO BUILD
UPSTREAM AS THE NEXT SURGE OF HEIGHT FALLS APPROACH THE WEST
COAST. SPAGHETTI PLOTS SUGGEST THE SPREAD HAS REDUCED RELATIVE TO
PREVIOUS MODEL CYCLES. IT IS WORTH THE NOTING THE 00Z GFS TRENDED
AWAY FROM ITS QUICKER ENSEMBLE MEAN AND MOVED TOWARD THE 12Z ECMWF
ENSEMBLE MEAN. GIVEN THE STRONG UPPER RIDGE TO THE WEST...WILL
TEND TO FAVOR SOMETHING SLOWER/DEEPER IN THIS REGION OF
UNCERTAINTY. THE PREFERENCE WILL FOCUS ON THE 12Z ECMWF ENSEMBLE
MEAN WITH THE 00Z GFS/12Z ECMWF BOTH IN SUPPORT OF ITS SOLUTION.


...REMNANTS OF ERIKA...

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

WHAT REMAINS OF ERIKA WILL GRADUALLY LIFT NORTHWARD ACROSS THE FAR
EASTERN GULF OF MX. MODELS VARY WITH THE STRENGTH OF THIS SYSTEM
BUT WILL DEFINITELY LEAN ON THE WEAKER SIDE GIVEN THE CURRENT
APPEARANCE OF THE FORMER TROPICAL CYCLONE. ON THE STRONGER END OF
THE SOLUTION ENVELOPE ARE THE 12Z CMC/UKMET WHICH ARE WAY TOO
AGGRESSIVE TO CONSIDER. MEANWHILE...THE 00Z NAM DOES BEGIN TO
DEVELOP A SURFACE LOW ACROSS THE EASTERN SIDE OF THE FL PANHANDLE
BY MIDDAY MONDAY. AS MENTIONED PREVIOUSLY...THE PLAN OF ATTACK IS
TO STAY MORE CONSERVATIVE MORE ALONG THE LINES OF THE 00Z GFS/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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