Preliminary Forecasts
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FXUS02 KWNH 290620
PREEPD

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

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

...ACTIVE AUTUMN WEATHER PATTERN IN THE WEST AND NORTHERN
ROCKIES...
...TROPICAL STORM MATTHEW EMERGES IN THE CARIBBEAN...

...OVERVIEW...
`TIS THE SEASON ACROSS THE LOWER 48---SNOW IN THE ROCKIES AND THE
THREAT OF TROPICAL WEATHER IN THE CARIBBEAN/SW ATLANTIC.
FORECASTING THE FALL-TRANSITION SEASON AND ACCOMPANYING VOLATILITY
HAS ALWAYS BEEN FUN. WILL MISS IT SOME, ESPECIALLY AT THE
NATIONAL-SCALE PERSPECTIVE.

...MODEL PREFERENCES...
THE 28/12Z FORECAST CYCLE LOOKED TO BE ON TRACK WITH THE KEY
SENSIBLE WEATHER FEATURES --- THIS MEDIUM RANGE PERIOD. TONIGHT`S
PACKAGE WAS A BLEND OF THE ECENS/GEFS, NAEFS AND CANADIAN MEANS
WITH SOME OF THE SMALLER-SCALE DETAILS EMBEDDED WITHIN THE 28/12Z
GFS --- ADDED FOR DETAIL.

ESPECIALLY ACROSS THE WEST THROUGH 4/12Z, 500MB TROUGH AXIS ALONG
110W IS DEPICTED NICELY BY GFS/ECMWF WITH COLD CORE OVER CENTRAL
WYOMING. FOR A DAY 5 DETERMINISTIC FORECAST---THIS IS ABOVE
AVERAGE AGREEMENT WITH RESPECT TO DEPTH, FORWARD SPEED AND THE
ABRUPT CHANGES ASSOCIATED WITH THIS PARTICULAR FEATURE. THIS
AMPLIFYING TROUGH ALLOWS THE DOWNSTREAM MID-LEVEL RIDGE TO
PROPAGATE EAST-NORTHEASTWARD ACROSS THE NATION`S MID SECTION, AND
KICK OUT THE STUBBORN MID-LEVEL CYCLONIC FLOW STALLED ACROSS THE
WESTERN OHIO VALLEY AND CENTRAL GREAT LAKES.

THE DETERMINISTIC 28/12Z GFS WORKS FROM WEST-TO-EAST --- EVEN IF
IT`S A TAD FASTER IN NEW ENGLAND WITH THE PROGRESSION OF THE
`FILLING CUTOFF` AND WITH THE SYNOPTIC-SCALE PATTERN ACROSS THE
SOUTHWEST ATLANTIC AFTER 4/12Z.

...UNCERTAINTY ASSESSMENT...
BY 5/00Z THOUGH --- THE DIFFERENCES LIE IN THE NORTHEAST GULF OF
MEXICO --- AS THE CANADIAN AND GFS USE A WEAK UPPER-LEVEL LOW IN
THE NERN GULF OF MEXICO TO KICK OUT `MATTHEW` ON A NORTHWARD
TRACK. THE ECMWF DOES NOT HAVE THIS FEATURE. JUST ABOUT EVERYTHING
ELSE IN THE DETERMINISTIC GUIDANCE UPSTREAM OF `MATTHEW` IS
SIMILAR FOR DAYS 6 AND 7. DID REACH OUT TO THE NHC FOR SOME `FEEL`
OF THE 4/12Z TO 6/12Z TIME FRAME --- JUST BEYOND THEIR OFFICIAL
FORECAST ENVELOPE. SO PLEASE REFER TO THE NHC FOR ALL THE DETAILS
CONCERNING `MATTHEW`.

THE DAY 6-7 CYCLONE EJECTING OUT OF THE NORTHERN ROCKIES AND UPPER
MISSOURI VALLEY FANS OUT ACROSS THE CENTRAL AND SOUTHERN PLAINS
--- AND HERE, LIKED THE 12Z GFS DETAIL WITH ITS DEPICTION OF THE
PACIFIC FRONTAL STRUCTURE AND FORWARD SPEED ROLLING OUT ACROSS THE
LOWER MISSOURI VALLEY AND SOUTH CENTRAL PLAINS VERSUS THE ECMWF.
ALONG THE WEST COAST HOWEVER...USING THE ENSEMBLE MEANS WILL HAVE
TO SUFFICE UNTIL THE LATITUDE OF LOW-AMPLITUDE WAVE ENERGY AND
`SPACING` BETWEEN SHORTWAVES SETTLES OUT.

...SENSIBLE WEATHER HIGHLIGHTS...
ACTIVE EARLY-OCTOBER WEATHER PATTERN ACROSS THE WEST, NORTHERN
ROCKIES AND PLAINS. AMPLIFYING PACIFIC TROUGH RELEASES DOWNWIND OF
THE CONTINENTAL DIVIDE ON DAY 5 AND MIGRATORY PACIFIC SURFACE HIGH
FOLLOWS --- WITH FAST-MOVING PACIFIC SHORTWAVE ENERGY DIRECTED
INTO THE PACIFIC NORTHWEST AND NORTHERN ROCKIES DURING THE LATTER
HALF OF THIS PARTICULAR MEDIUM RANGE PERIOD.

STRONG SURFACE RIDGE AND NORTHEAST ONSHORE FLOW ANCHORS ACROSS
EASTERN SEABOARD DURING THE LATTER HALF OF THE FORECAST PERIOD.
COOLER NORTH ATLANTIC FLOW IS ANTICIPATED FOR THE NORTHEAST AND
MID-ATLANTIC COASTAL PLAINS---IN ADVANCE OF THE PROJECTED PATH OF
`MATTHEW`.

VOJTESAK


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