Prognostic Meteorological Discussion
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000
FXUS02 KWBC 291534
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1134 AM EDT THU SEP 29 2016

VALID 12Z SUN OCT 02 2016 - 12Z THU OCT 06 2016

...PATTERN OVERVIEW AND UNCERTAINTY ASSESSMENT...

A CUTOFF UPPER-LEVEL LOW IS FORECAST BY ALL GUIDANCE TO BE IN
PLACE ACROSS THE LOWER GREAT LAKES AT THE BEGINNING OF DAY 3 /12Z
SUN. AT THIS TIME THE UPPER LOW WILL BE IN THE PROCESS OF
GRADUALLY WEAKENING AND MOVING EAST. HEREIN LIES ONE AREA OF
UNCERTAINTY EARLY ON, WITH RESPECT TO HOW QUICKLY THIS LOW WEAKENS
AND MOVES EAST. THE 00Z ECMWF WEAKENS THE SYSTEM AND MOVES IT EAST
MUCH MORE QUICKLY THAN THE GFS. FARTHER SOUTH, ANOTHER INITIAL
AREA OF UNCERTAINTY EXISTS WITH A SHORTWAVE ACROSS THE LOWER MS
VALLEY/SOUTHEAST ON SUNDAY AND MONDAY. THE 00Z ECMWF IS LESS
AMPLIFIED WITH THIS WAVE RELATIVE TO THE GFS. BOTH OF THESE
SYSTEMS HAVE AN IMPACT ON THE EVENTUAL TRACK OF WHAT IS FORECAST
BY THE NATIONAL HURRICANE CENTER TO BE HURRICANE MATTHEW. DUE TO
THE FASTER NORTHERN STREAM WAVE, AND THE WEAKER SOUTHERN STREAM
WAVE, THE 00Z ECMWF HAS LITTLE TO PICK UP MATTHEW AND MOVE IT
NORTHWARD, AND THUS SHOWS A SUBSTANTIALLY SLOWER SOLUTION RELATIVE
TO THE 00Z/06Z GFS AS WELL AS THE 00Z GEM GLOBAL. THE OFFICIAL NHC
FORECAST TRACK IS SIMILAR TO THE GFS/GEFS MEAN SOLUTIONS, ALBEIT A
BIT SLOWER.

FARTHER WEST, A LARGE TROUGH/UPPER LOW IS FORECAST BY ALL GUIDANCE
TO MOVE INTO THE WEST COAST ON SUNDAY. MODEL SPREAD WITH RESPECT
TO THIS FEATURE IS INITIALLY LOW, BUT INCREASES SUBSTANTIALLY BY
DAY 5 /12Z TUES. THE WPC FORECAST FAVORED A BLEND OF THE 06Z GEFS
MEAN/00Z ECMWF ENS MEAN, WITH A LESSER COMPONENT OF THE 00Z GFS,
WHICH DOES NOT AMPLIFY THE WAVE NEAR AS MUCH AS THE 06Z GFS, WHICH
CLOSES OFF AN ANOMALOUS UPPER LOW ACROSS THE SOUTHERN PLAINS BY
DAYS 6-7.

FINALLY, AN ADDITIONAL SHORTWAVE WILL APPROACH THE NORTHWESTERN
U.S. COAST DURING THE DAY 6-7 TIME PERIOD. DUE TO THE RELATIVELY
SHALLOW NATURE OF THIS WAVE, TIMING DIFFERENCES ARE QUITE
SUBSTANTIAL AND UNCERTAINTY IS HIGH. THE WPC FORECAST FOR THIS
TIME PERIOD WAS LARGELY BASED ON A BLEND OF THE 06Z GEFS MEAN/00Z
ECMWF ENS MEAN, WITH A SMALL COMPONENT OF THE 00Z GFS.

...SENSIBLE WEATHER HIGHLIGHTS...

THE LINGERING UPPER LOW ACROSS THE LOWER GREAT LAKES/NORTHEAST
DURING DAYS 3-4 WILL SUPPORT CONTINUED SHOWER/THUNDERSTORM
ACTIVITY ACROSS THESE AREAS. HEAVY RAIN IS POSSIBLE ACROSS
PORTIONS OF EASTERN NEW ENGLAND WHERE A BETTER FETCH OF TROPICAL
MOISTURE MAY FEED INTO THE SYSTEM. AFTER THAT TIME ALL EYES ON THE
EASTERN SEABOARD WILL TURN TO ANY POSSIBLE EFFECTS FROM MATTHEW.
PLEASE REFER TO PRODUCTS ISSUED BY THE NATIONAL HURRICANE CENTER
FOR THE OFFICIAL FORECAST TRACK FOR MATTHEW. DEPENDING ON THE
EXACT TRACK, SOME POTENTIAL IMPACTS SUCH AS HIGH SURF, HEAVY RAIN,
AND STRONG WINDS COULD IMPACT POSITIONS OF THE EASTERN SEABOARD BY
THE MIDDLE OF NEXT WEEK.

THE LARGE TROUGH/UPPER LOW FORECAST TO MOVE ACROSS THE WEST DURING
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, AND SURFACE LOW PRESSURE DEVELOPS
ACROSS THE NORTHERN PLAINS, GOOD INFLOW OF MOISTURE INTO THE
SYSTEM SHOULD SUPPORT PERIODS OF SHOWERS AND THUNDERSTORMS, WITH
SOME POTENTIAL FOR HEAVY RAINFALL ACROSS THE NORTHERN PLAINS/UPPER
MIDWEST AS WELL AS EASTERN PORTIONS OF THE NORTHERN ROCKIES, WHERE
UPSLOPE FLOW COULD OCCUR. 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.


RYAN


$$




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