Prognostic Meteorological Discussion
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000
FXUS10 KWNH 290646
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
246 AM EDT SAT AUG 29 2015

VALID AUG 29/0000 UTC THRU SEP 01/1200 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.


...NORTHERN STREAM SHORTWAVE MOVING FROM THE GREAT LAKES BEFORE
SHEARING DOWNSTREAM...

FINAL PREFERENCE: A NON-00Z ECMWF/12Z ECMWF ENSEMBLE MEAN SOLUTION
FORECAST CONFIDENCE: ABOVE AVERAGE

A GRADUALLY SHEARING NORTHERN STREAM FEATURE WILL CONTINUE TO
MIGRATE EASTWARD FROM THE UPPER GREAT LAKES TOWARD LOCATIONS
FARTHER DOWNSTREAM. AS HAS BEEN THE CASE IN RECENT DAYS...THE
ECMWF SUITE HAS BEEN SLOWER WITH EJECTION OF THIS TROUGH. THIS
SEEMS TO ESCAPE THE STRONGER CONSENSUS SO WILL FAVOR A NON-00Z
ECMWF/12Z ECMWF ENSEMBLE MEAN SOLUTION.


...GENERAL MID-LEVEL WEAKNESS ACROSS THE SOUTHERN U.S...

FINAL PREFERENCE: BLEND OF THE 00Z NAM/GFS/ECMWF
FORECAST CONFIDENCE: SLIGHTLY BELOW AVERAGE

MODELS AGREE THAT AN ELONGATED BLOB OF VORTICITY CENTERS WILL
MEANDER ABOUT THE SOUTHERN U.S. THROUGHOUT MUCH OF THE PERIOD. THE
EASTERN BATCH OF SHORTWAVE ENERGY IS EXPECTED TO LIFT NORTH AND
EAST APPROACHING THE SOUTHERN MID-ATLANTIC BY EARLY MONDAY. THE
00Z NAM/GFS/ECMWF ARE QUITE SIMILAR TO THE ENSEMBLE MEANS WITH
THIS OVERALL EVOLUTION. THE 00Z NAM MAY BECOME A HAIR TOO SLOW
EJECTING THIS SYSTEM OFF THE ATLANTIC COAST BUT ITS SOLUTION
APPEARS TO BE WITHIN GENERAL TOLERANCE.

TO THE WEST...ANOTHER MID-LEVEL WEAKNESS IS FORECAST TO SLOWLY
RETROGRADE TOWARD THE LOWER MS VALLEY/OZARKS REGION. THE 00Z
GEFS/12Z ECMWF ENSEMBLE/21Z SREF MEANS ARE RATHER SIMILAR AT THE
END OF THE PERIOD....01/1200Z...WITH SUPPORT FROM THE 00Z
NAM/GFS/ECMWF. WILL FAVOR A GENERAL BLEND OF THE 00Z NAM/GFS/ECMWF
FOR BOTH OF THESE SYSTEMS.


...MEAN UPPER TROUGH ANCHORING THE WESTERN STATES THROUGHOUT THE
PERIOD...

FINAL PREFERENCE: BLEND OF THE 00Z GEFS/21Z SREF MEANS
FORECAST CONFIDENCE: BELOW AVERAGE

A RATHER POTENT BLOCK ACROSS THE OPEN PACIFIC HAS CONTINUED TO
FORCE A DEEP UPPER TROUGH ACROSS THE EASTERN PACIFIC/WESTERN U.S.
INITIALLY A PAIR OF SYSTEMS WILL INHABIT THE EASTERN/NORTHEASTERN
PACIFIC WITH THE LEAD SYSTEM MOVING INTO THE PACIFIC NORTHWEST BY
JUST AFTER 29/1200Z. THESE 500-MB HEIGHT FALLS SHOULD QUICKLY LIFT
NORTHEASTWARD INTO WESTERN CANADA WHILE THE REMAINDER OF THE UPPER
TROUGH DESCENDS ON THE NORTHWESTERN STATES. THROUGH
31/0000Z...THERE IS SOME VARIABILITY IN THE SOLUTIONS BUT ALL
FAVOR A SIMILAR PLACEMENT OF THE LONGWAVE TROUGH. THEREAFTER...THE
SPREAD BECOMES A BIT LARGER WITH THE 00Z NAM BECOMING SLOWER AND
THE 00Z CMC QUICKER EJECTING THE BAROCLINIC ZONE THROUGH THE GREAT
PLAINS ON MONDAY. THE ENSEMBLE MEANS BECOME A MORE STABLE
ALTERNATIVE MOVING INTO DAY 3. THE DIFFERENCES BECOME MUCH LARGER
UPSTREAM AS THE TROUGH RELOADS OVER VANCOUVER ISLAND. THE FACT A
STRONG BLOCK EXISTS TO THE WEST MAKES ONE BELIEVE THE PROGRESSIVE
ECMWF SUITE DOES NOT SEEM NEARLY AS FEASIBLE. THE SLOWER/MORE
AMPLIFIED SOLUTION PAINTED BY THE 00Z GFS SEEMS MORE LIKELY. GIVEN
THE SPREAD IN THE SPAGHETTI PLOT...DO NOT PLAN ON FULLY USING ITS
SOLUTION BUT TAKING A COMBINATION OF THE 00Z GEFS/21Z SREF MEANS
GIVEN THEY PORTRAY THE IDEA IN A MORE DAMPENED STATE. THIS
PARTICULAR SOLUTIONS HAS GAINED SOME CONFIDENCE AS THE 00Z ECMWF
DID SHOW A TREND IN THIS DIRECTION.


...TROPICAL STORM ERIKA...

FINAL PREFERENCE: BLEND OF THE 00Z GFS/12Z ECMWF PER NHC FORECAST
TRACK
FORECAST CONFIDENCE: N/A

THE 03Z NHC FORECAST PACKAGE SHOWED THIS WEAK TROPICAL STORM ALONG
THE SOUTHWESTERN EXTENT OF HISPANIOLA WITH A GENERAL NORTHWESTWARD
TRACK TAKING IT INTO THE FAR EASTERN GULF OF MX. ITS STRENGTH IS
VERY UNCERTAIN AFTER EVALUATING THE GUIDANCE AND LISTENING TO THE
HURRICANE HOTLINE CALL. THERE HAS DEFINITELY BEEN A DOWNWARD TREND
IN THE 00Z MODELS REGARDING THE INTENSITY FORECAST.
OVERALL...THERE IS ALSO A LOT OF SPREAD IN THE TROPICAL CYCLONE
TRACKS WITH THE 00Z/12Z CMC WELL EAST WHILE RAPIDLY DEEPENING
ERIKA. MEANWHILE...THE 00Z/12Z UKMET FOLLOW THE NHC TRACK BUT ARE
MUCH QUICKER/STRONGER. THE 00Z GFS/12Z ECMWF SOMEWHAT HANDLE THE
TRACK BUT PERHAPS OFF TO THE WEST A BIT. THE CLOSEST SOLUTION TO
THE 03Z TROPICAL ADVISORY IS A 00Z GFS/12Z ECMWF BLEND. CHOSE TO
NOT INCLUDE THE LATEST 00Z ECMWF AS IT WAS EVEN WEAKER AND SPLITS
THE WEAK LOW-LEVEL CENTER INTO TWO DIFFERENT ENTITIES ACROSS 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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