Prognostic Meteorological Discussion
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000
FXUS10 KWNH 300639
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
238 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 MODEL GUIDANCE ALONG WITH FINAL
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...

FINAL PREFERENCE: A NON-00Z/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 00Z/12Z
UKMET SHOW MORE AMPLIFICATION SO THESE 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...

FINAL PREFERENCE: FIRST SYSTEM: MODEL COMPROMISE BETWEEN THE 00Z
NAM/GFS/ECMWF...SECOND SYSTEM: A NON-00Z/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
LOWER MID-ATLANTIC DURING THE NEXT 24 TO 36 HOURS. THE 00Z
NAM/GFS/ECMWF ARE IN NEAR ALIGNMENT WHILE THE 00Z CMC/UKMET HAVE
IMPROVED THEIR SOLUTIONS BUT STILL DIVERGE SOMEWHAT FROM THE
FORMER CLUSTER. THE PREFERENCE WILL BE A COMPROMISE BETWEEN THE
00Z NAM/GFS/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 00Z/12Z CMC DO TEND TO DRAG SOME OF THE
VORTICITY FARTHER EAST THAN OTHER SOLUTIONS. THUS...WILL LEAN ON A
NON-00Z/12Z CMC MODEL COMPROMISE WITH THIS ARRAY OF SYSTEMS.


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

FINAL PREFERENCE: BLEND OF THE 00Z GFS/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 00Z/12Z UKMET ARE 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 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/ECMWF BOTH IN SUPPORT OF ITS
SOLUTION. THE 00Z ECMWF DID MAKE A SUBTLE ADJUSTMENT TOWARD THE
SLOWER SIDE BUT THERE IS STILL PLENTY OF ENSEMBLE SUPPORT FOR THIS
SCENARIO AS WELL.


...REMNANTS OF ERIKA...

FINAL PREFERENCE: BLEND OF THE 00Z GFS/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. THE PREVIOUSLY STRONGER
SOLUTIONS...12Z CMC/UKMET...HAVE BOTH TRENDED IN THE WEAKER
DIRECTION. 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/ECMWF.
HOWEVER...IT IS WORTH NOTING THE REMNANT CIRCULATION WILL
ENCOUNTER MUCH FAVORABLE TROPICAL CHARACTERISTICS FOR
DEVELOPMENT...WARM SSTS AND WEAKENING VERTICAL SHEAR. THUS...IT IS
STILL WORTH MONITORING...PARTICULARLY GIVEN THE ALREADY IMPRESSIVE
HEAVY RAINFALL THREAT FOR FL.

...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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