Prognostic Meteorological Discussion
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000
FXUS02 KWBC 311536
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1135 AM EDT WED AUG 31 2016

VALID 12Z SAT SEP 03 2016 - 12Z WED SEP 07 2016

...STRENGTHENING TROPICAL DEPRESSION NINE EXPECTED TO AFFECT THE
EASTERN SEABOARD...


...OVERVIEW...

TWO AREAS WILL BE OF INTEREST DURING THE PERIOD... THE EAST COAST
WHICH MAY SEE SOME EFFECTS FROM T.D. NINE EXTENDING FROM THE SHORT
RANGE PERIOD AND THEN FROM THE NRN HALF OF THE PLAINS INTO THE
UPR/WRN GREAT LAKES WHERE A SLOW MOVING WAVY FRONT WILL PROVIDE A
FOCUS FOR A POTENTIALLY MULTI-DAY EVENT OF LOCALLY HVY AND IN SOME
CASES STRONG CONVECTION. BOTH AREAS/EVOLUTIONS HAVE THEIR
UNCERTAINTIES BUT GUIDANCE REMAINS GENERALLY WELL CLUSTERED FOR
THE LARGE SCALE PATTERN CONSISTING OF A STRONG EASTERN PAC
RIDGE... WRN U.S. TROUGH THAT SHOULD GRADUALLY BROADEN WITH
TIME... AND A BUILDING RIDGE ACROSS EASTERN NORTH AMERICA.


...GUIDANCE/UNCERTAINTY ASSESSMENT...

THE 00Z ECMWF/06Z GEFS PROVIDED A BASIS FOR THE FCST. A BLEND OF
THESE SOLUTIONS ALLOWS FOR MANAGEABLE ADJUSTMENTS TO ACCOMMODATE
THE OFFICIAL NHC FCST FOR T.D. NINE AND ITS EVENTUAL EXTRATROPICAL
EVOLUTION OVER THE WESTERN ATLANTIC BY DAY 4. THIS BLEND ALSO
REFLECTS A FASTER TREND AMONG THE GUIDANCE FOR THE SYSTEM CROSSING
CANADA AND ITS COLD FRONT EXTENDING INTO THE NORTHERN PLAINS.

GUIDANCE TRENDS FOR T.D. NINE OVER THE PAST DAY HAVE BEEN WESTWARD
A BIT CLOSER TO THE EAST COAST BUT NOT TO THE EXTENT OF THE
WESTERN SIDE OF THE ENVELOPE THAT INCLUDED THE 00Z UKMET/CMC AND
12Z NAM. IT WILL BE AROUND THE START OF THE PERIOD ON SAT WHEN
T.D. NINE SHOULD BE IN THE PROCESS OF INTERACTING WITH NRN STREAM
TROUGH ENERGY DROPPING SOUTHEASTWARD FROM THE GREAT LAKES. THE
SYSTEM IS THEN FORECAST TO LIFT NORTHWARD BETWEEN THE BUILDING
EASTERN U.S. RIDGE AND ANOTHER RIDGE TO THE E OF BERMUDA.
PLACEMENT BETWEEN THESE RIDGES AND THE DEGREE OF INTERACTION WITH
THE NORTHERN STREAM SHORTWAVE ENERGY WILL LIKELY PROVIDE SOME
ONGOING FCST CHALLENGES FOR TRACK AND TIMING.

FARTHER WEST... MODELS HAVE TRENDED FASTER AND SLIGHTLY MORE
AMPLIFIED WITH SHORTWAVE ENERGY MOVING FROM THE ROCKIES INTO THE
PLAINS BY DAYS 6/7. AS A RESULT THE EASTWARD PROGRESSION OF THE
FRONTAL SYSTEM ACROSS THE CENTRAL U.S. IS A BIT FASTER WITH THIS
FORECAST PACKAGE RELATIVE TO THE PREVIOUS ONE. ULTIMATELY THE
TIMING OF THIS SHORTWAVE ENERGY WILL BE RELIANT ON HOW QUICKLY A
CLOSED UPPER LOW OVER THE ALEUTIANS BREAKS DOWN AND EJECTS ENERGY
EASTWARD AROUND NORTHERN SIDE OF THE EAST PACIFIC RIDGE.


...WEATHER HIGHLIGHTS/THREATS...

THOSE WITH INTERESTS ALONG THE MID ATLC/NORTHEAST COAST SHOULD
CONTINUE TO MONITOR FCSTS FOR T.D. NINE AND ITS EVENTUAL
EXTRATROPICAL EVOLUTION. COASTAL AREAS MAY SEE STRONG WINDS AND
POTENTIALLY HEAVY RAINFALL DEPENDING ON EXACT TRACK OF THE SYSTEM.
FARTHER SWD A LINGERING FRONT NEAR THE ERN GULF COAST AND ACROSS
FLORIDA MAY PROVIDE SOME ADDED FOCUS FOR DIURNALLY ENHANCED
CONVECTION.  MOIST FLOW MAY ALSO PROMOTE AREAS OF RAINFALL
ALONG/INLAND FROM THE WRN HALF OF THE GULF COAST. ASIDE FROM RUN
TO RUN ADJUSTMENTS IN SPECIFICS... FORECASTS HAVE BEEN FAIRLY
CONSISTENT IN SHOWING HEAVY RAIN POTENTIAL FROM THE NRN-CNTRL
PLAINS INTO THE MIDWEST/GREAT LAKES. TRAINING/REPEAT ACTIVITY WILL
BE POSSIBLE AS ESTABLISHMENT OF SWLY FLOW ALOFT AHEAD OF THE WRN
TROUGH ALOFT WILL RESULT IN VERY SLOW PROGRESS OF THE WAVY FRONT
OVER THE NRN PLAINS. THE POTENTIAL FOR SOME CONVECTION TO BE
STRONG IS BEING MONITORED BY SPC AS WELL. THE NRN ROCKIES/HIGH
PLAINS WILL LIKELY SEE A PERIOD OF RAINFALL THAT COULD BE LOCALLY
ENHANCED.

EXPECT BELOW NORMAL TEMPS TO PREVAIL FROM MUCH OF THE WEST INTO
THE NORTHERN PLAINS. CLOUDS AND RAINFALL MAY LEAD TO SOME MINUS
10-20F ANOMALIES FOR HIGHS OVER PARTS OF THE NRN ROCKIES/HIGH
PLAINS EARLY NEXT WEEK. ON THE OTHER HAND THE UPPER RIDGE BUILDING
INTO THE EAST SHOULD PROMOTE A WARMING TREND AND A BROAD AREA OF
PLUS 5-15F ANOMALIES... AND PERHAPS LOCALLY HIGHER... FOR MAX
TEMPS FROM MON ONWARD. TEMPS ALONG THE NRN HALF OF THE EAST COAST
WILL BE SENSITIVE TO THE TRACK OF T.D. NINE.

RYAN

$$





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