Prognostic Meteorological Discussion
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FXUS02 KWBC 281544
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1143 AM EDT WED SEP 28 2016

VALID 12Z SAT OCT 01 2016 - 12Z WED OCT 05 2016

...PATTERN OVERVIEW AND UNCERTAINTY ASSESSMENT...

A CUTOFF UPPER-LEVEL LOW IS FORECAST BY ALL GUIDANCE TO BE IN
PLACE ACROSS THE OHIO VALLEY AT THE BEGINNING OF DAY 3 /12Z SAT,
WHICH WILL THEN LIFT SLOWLY NORTH AND EASTWARD AS IT WEAKENS.
FARTHER WEST, A SECOND UPPER LOW IS FORECAST TO BE CENTERED JUST
OFF THE BRITISH COLUMBIA COAST, WITH SHORTWAVE ENERGY TO ITS SOUTH
MOVING INTO NORTHERN CA/THE PAC NW. IN BETWEEN THESE TWO FEATURES,
UPPER-LEVEL RIDGING IS FORECAST TO EXTEND NORTH FROM MEXICO INTO
THE PLAINS. FORECAST UNCERTAINTY IN THE LARGE SCALE PATTERN IS
INITIALLY RELATIVELY LOW ON DAYS 3 AND 4, WITH MODEL SPREAD
INCREASING SUBSTANTIALLY IN THE DAY 5-7 TIME FRAME.

THE EXACT EVOLUTION OF THE LARGE SCALE PATTERN ACROSS NORTH
AMERICA AND THE NORTH ATLANTIC OCEAN WILL AFFECT THE EVENTUAL
TRACK OF WHAT IS FORECAST BY THE NATIONAL HURRICANE CENTER TO BE
HURRICANE MATTHEW. A BLEND OF THE 00Z GFS/GEFS MEAN/ECMWF ENS MEAN
WAS USED FOR THE WPC MEDIUM RANGE FORECAST. THE 00Z DETERMINISTIC
ECMWF BECOMES AN APPARENT OUTLIER SOLUTION WITH RESPECT TO THE
EVOLUTION OF THE PATTERN ACROSS THE NORTHEASTERN U.S./NORTH
ATLANTIC BY DAYS 6-7, KEEPING THE UPPER LOW INTACT AND FARTHER
WEST MUCH LONGER THAN ANY OTHER DETERMINISTIC SOLUTION AS WELL AS
THE 00Z EC ENS MEAN, THUS THIS SOLUTION WAS NOT INCLUDED IN THE
BLEND. THE OFFICIAL FORECAST TRACK FROM THE NATIONAL HURRICANE
CENTER FOR MATTHEW SEEMS TO FIT A COMPROMISE BETWEEN THE GFS/GEFS
AND ECMWF/ECMWF ENSEMBLE SOLUTIONS.

FARTHER WEST, SPREAD ALSO INCREASES FAIRLY SUBSTANTIALLY FROM DAY
5 ONWARD, PRIMARILY WITH RESPECT TO THE PROGRESSION OF THE
TROUGH/UPPER LOW THAT EVOLVES ACROSS THE WESTERN U.S. THE
AFOREMENTIONED BLEND APPEARS TO REPRESENT A GOOD MIDDLE GROUND
SOLUTION ACROSS THE WEST AS WELL, BETWEEN THE QUICKER GFS/GEFS AND
THE SLOWER ECMWF/ECMWF ENSEMBLE MEAN. THIS BLEND HOLDS THROUGH
DAYS 6-7 AS THE SYSTEM MOVES INTO THE CENTRAL U.S.


...SENSIBLE WEATHER HIGHLIGHTS...

THE PERSISTENT UPPER LOW INITIALLY ACROSS THE OHIO VALLEY WILL
SUPPORT CONTINUED SHOWER ACTIVITY ALONG PORTIONS OF THE EAST
COAST, GREAT LAKES, AND NORTHEAST ON SATURDAY AND SUNDAY. AFTER
THAT TIME ALL EYES ON THE EASTERN SEABOARD WILL TURN TO THE
POSSIBLE IMPACTS 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 AS HIGH SURF, HEAVY RAIN AND STRONG WINDS COULD BEGIN TO AFFECT
THE EASTERN SEABOARD DURING THE MEDIUM RANGE FORECAST PERIOD.

ACROSS THE WEST, THE LARGE TROUGH/UPPER-LOW FORECAST TO EVOLVE
DURING THE MEDIUM RANGE WILL SUPPORT AREAS OF PRECIPITATION AND
GUSTY WINDS, ALONG WITH GRADUALLY LOWERING SNOW LEVELS DURING THE
SUNDAY TO TUESDAY TIME PERIOD. AS THE SYSTEM MOVES INTO THE
CENTRAL U.S. LATE IN THE MEDIUM RANGE, AND SURFACE LOW PRESSURE
DEVELOPS ACROSS THE NORTHERN PLAINS, GOOD INFLOW OF MOISTURE AND A
STATIONARY FRONTAL BOUNDARY NORTHEAST OF THE SURFACE LOW COULD
SUPPORT PERIODS OF SHOWERS AND THUNDERSTORMS, WITH SOME POTENTIAL
FOR HEAVY RAINFALL AMOUNTS.

RYAN

$$





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