Prognostic Meteorological Discussion
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000
FXUS02 KWBC 301541
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1141 AM EDT FRI SEP 30 2016

VALID 12Z MON OCT 03 2016 - 12Z FRI OCT 07 2016

...OVERVIEW...

A COLD FRONT WILL WORK ITS WAY OUT OF THE ROCKIES AND THROUGH THE
PLAINS TOWARD THE APPALACHIANS NEXT WEEK. A LINGERING COLD FRONT
WILL REMAIN OFFSHORE THE SOUTHEAST STATES, AND THE NATIONAL
HURRICANE CENTER FORECASTS HURRICANE MATTHEW TO BE MOVING
NORTHWARD THROUGH THE BAHAMAS LATE TUESDAY AND THEN POTENTIALLY
OFF THE EAST COAST AFTER THAT. PRECIPITATION WILL RETURN TO THE
PACIFIC NORTHWEST BY LATE NEXT WEEK.


...GUIDANCE PREFERENCES AND UNCERTAINTY ASSESSMENT...

FORECAST UNCERTAINTY HAS DECREASED SOMEWHAT RELATIVE TO THIS TIME
YESTERDAY WITH RESPECT TO THE FLOW PATTERN ACROSS THE EASTERN U.S.
EARLY IN THE MEDIUM RANGE, WHICH INFLUENCES THE EVENTUAL TRACK OF
HURRICANE MATTHEW. MODEL SPREAD WITH RESPECT TO A SHORTWAVE
INITIALLY OVER THE SOUTHEASTERN U.S. AT THE START OF DAY 3 /00Z
MONDAY HAS DECREASED, WITH THE PREVIOUSLY MORE AMPLIFIED GFS AND
LESS AMPLIFIED ECMWF MOVING TOWARD A MIDDLE GROUND WITH THEIR MOST
RECENT RUNS. THUS, THE RESPECTED FORECAST TRACKS FOR HURRICANE
MATTHEW HAVE BEGUN TO MOVE TOWARD EACH OTHER AS WELL, ALTHOUGH
DIFFERENCES DO REMAIN WITH THE 00Z ECMWF REMAINING SLOWER/FARTHER
EAST RELATIVE TO THE 00Z/06Z GFS RUNS. THE OFFICIAL FORECAST TRACK
FROM THE NATIONAL HURRICANE CENTER IS RELATIVELY CLOSE TO THE 06Z
GFS, ALTHOUGH A BIT SLOWER. FARTHER NORTH, GUIDANCE HAS ALSO COME
INTO BETTER AGREEMENT WITH RESPECT TO THE UPPER LOW INITIALLY
ACROSS THE NORTHEASTERN U.S. ON DAY 3, WHICH MOVES SOMEWHAT SLOWLY
EAST INTO THE NORTH ATLANTIC BY DAY 5. THERE ARE SOME DIFFERENCES
IN HOW QUICKLY THIS FEATURES WEAKENS BY DAY 7, WITH THE 00Z ECMWF
KEEPING THE LOW STRONGER RELATIVE TO THE GFS AND CMC. A BLEND OF
THE 06Z GFS/GEFS MEAN AND TO A LESSER DEGREE THE 00Z ECMWF/00Z
ECMWF ENS MEAN WAS USED AS A BASIS FOR FOR THE WPC FORECAST, WITH
MORE WEIGHTING ON THE DETERMINISTIC SOLUTIONS EARLY ON (AND MORE
WEIGHT ON THE DETERMINISTIC 06Z GFS IN THE VICINITY OF HURRICANE
MATTHEW).

FARTHER WEST, A LARGE UPPER LOW WILL BE CROSSING THE CENTRAL
ROCKIES AND MOVING INTO THE NORTHERN PLAINS DURING THE DAY 3-4
TIME PERIOD. THE 00Z ECMWF/ECMWF ENSEMBLE MEAN ARE A LITTLE
QUICKER TO MOVE THIS LOW EAST THAN CONSENSUS. BY DAYS 6-7 ANOTHER
SHORTWAVE WILL APPROACH THE PAC NW COAST. WHILE THERE IS QUITE A
BIT OF DETERMINISTIC AND ENSEMBLE MEMBER SPREAD WITH RESPECT TO
THIS WAVE, THERE IS ACTUALLY VERY GOOD AGREEMENT FOR DAY 7 AMONG
THE 06Z GEFS MEAN AND 00Z ECMWF ENS/CANADIAN ENS MEANS. THUS,
TRENDED BLEND FOR WPC FORECAST MORE TOWARD THE 06Z GEFS/00Z ECMWF
ENS MEANS BY DAYS 6-7.


...WEATHER HIGHLIGHTS...

SHOWERS WILL SLOWLY EXIT THE NORTHEAST AS THE UPPER LOW WEAKENS
AND DRIFTS EASTWARD. A DRIER AND MILDER AIRMASS WILL BECOME
DOMINANT, THOUGH NORTHEAST FLOW FROM SFC HIGH PRESSURE OVER NOVA
SCOTIA WILL KEEP TEMPERATURES NEAR OR A BIT BELOW AVERAGE EAST OF
THE APPALACHIANS. GIVEN THE OFFICIAL NHC FORECAST TRACK FOR
HURRICANE MATTHEW TAKING THE SYSTEM INTO THE BAHAMAS BY TUES/WED,
ANY IMPACTS ON THE EASTERN SEABOARD SHOULD BE LIMITED TO SOME
POTENTIALLY HIGH SURF. SOME UNCERTAINTY REMAINS, HOWEVER, AND
THOSE ALONG THE EAST COAST SHOULD CONTINUE TO MONITOR THE FORECAST
FOR MATTHEW FROM NHC.

THE LARGE TROUGH/UPPER LOW FORECAST TO MOVE ACROSS THE WEST EARLY
IN THE MEDIUM RANGE WILL BRING AREAS OF PRECIPITATION AND
POTENTIALLY GUSTY WINDS, ALONG WITH COLDER TEMPERATURES AND
GRADUALLY LOWERING SNOW LEVELS BY EARLY NEXT WEEK. AS THE SYSTEM
BEGINS TO MOVE INTO THE CENTRAL U.S. BY LATE MONDAY, SURFACE LOW
PRESSURE IS FORECAST TO DEVELOP ACROSS THE NORTHERN PLAINS. GOOD
INFLOW OF MOISTURE INTO THE SYSTEM SHOULD SUPPORT PERIODS OF
SHOWERS AND THUNDERSTORMS AHEAD OF THE COLD FRONT ACROSS THE
SOUTHERN CENTRAL PLAINS AS WELL AS FARTHER NORTH CLOSER TO THE SFC
LOW AND STATIONARY FRONT. THERE CONTINUES TO BE SOME POTENTIAL FOR
HEAVY RAINFALL ACROSS THE NORTHERN PLAINS/UPPER MIDWEST AS WELL AS
EASTERN PORTIONS OF THE NORTHERN ROCKIES, WHERE UPSLOPE FLOW COULD
ENHANCE PRECIPITATION AMOUNTS. ADDITIONALLY, THE POTENTIAL EXISTS
FOR SEVERE THUNDERSTORMS ACROSS PORTIONS OF THE SOUTHERN/CENTRAL
PLAINS DURING THE TUESDAY/TUESDAY NIGHT TIME FRAME PER SPC
CONVECTIVE OUTLOOKS.

FINALLY, THE SHORTWAVE/SFC FRONTAL SYSTEM ARRIVING ALONG THE
NORTHWEST U.S. COAST LATE IN THE MEDIUM RANGE SHOULD SPREAD
PRECIPITATION INTO THE PAC NW, WITH SNOW LEVELS LOWERING BY THURS
NIGHT/FRIDAY AS THE TROUGH BEGINS TO MOVE INLAND.

RYAN

$$





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