Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 291028

Area Forecast Discussion
National Weather Service Portland Oregon
327 AM PDT Thu Sep 29 2016

.SYNOPSIS...Another great early autumn day for the region today, with
mild temperatures and mix of sun and clouds. Bit cooler on Friday,
with more clouds thanks to low pressure approaching from the Gulf of
Alaska. This low will spread showers into the region on Saturday,
with even period of rain later Saturday night into Sunday. Then a
break in the weather for Monday, but unsettled weather continues next

.SHORT TERM...(Today through Sunday)...Another great early autumn day
on tap for today across the region, with generally partly to mostly
sunny skies and temperatures down just a tad.  Areas of low clouds
along the coast will break up this morning, with partly cloudy skies
there for rest of the day.

Upper low pressure over the southeast Gulf of Alaska is slowly
approaching, and turning the upper flow more southwesterly. This will
allow for occasional high clouds over the region today. A weak
disturbance in the flow will move across southwest Oregon and
northeast into central Oregon this evening. Not much in way of
moisture aloft, but may be enough to support a shower or even a
thunderstorms over the high Cascades of Oregon later today. Will keep
current chance of such in the forecast for late this afternoon into
early this evening to south of Mt Hood. But better threat of showers
and thunderstorms will be to east of the Cascades across
central/southeast Oregon.

The low will draw closer tonight and Fri, but will remain far enough
offshore that any bands of showers will likely stay over the Pac. But
will see increasing chance of showers along the coast by early
afternoon as moisture around the low gets closer. Should remain
generally dry inland, though will keep a 20 pct PoP over the Cascades
in the afternoon as weak instability and better mid-level moisture
could support an isolated shower or two in that area.

The low slowly spreads onshore Friday night and Saturday with a
decent short wave associated with the main low center rotating
onshore through the base of the low late Friday night and Saturday.
This should increase the showers by Saturday. Snow levels drop
dramatically in the Cascades late Fri night and Saturday, likely to
be between 5000 and 5500 feet. But with ground still warm, any
accumulation likely to be only a inch or so.

A second drops south in the wake of the first low and moves into
southwest Oregon and northern California on Sun. Models still
suggesting main thrust of energy will head south of our area. Suspect
will see occasional rain along the Coast Sat night, spreading inland
overnight into Sunday morning. As the low heads farther south, rain
will transition to showers and decrease over the northern zones in
the afternoon.      rockey.

.LONG TERM...(Saturday night through Wednesday)...No changes. Model
guidance continues to struggle a bit through the extended period
with the precise evolution of the upper trough that is moving across
the region. Latest trends suggest the trough may end up tracking a
bit more south and west, though the ECMWF continues to depict more
moisture than the latest, drier GFS solution. As a result, decreased
PoPs a bit on Sunday for many portions - particularly across the
northern and western portions of the forecast area - but still
maintained widespread chance PoPs across the area. Models diverge in
the timing of a pair of disturbances that may bring a couple of
rounds of lighter precipitation early next week, so have maintained
a generalized chance of showers for the end of the period. Snow
levels look to remain below 6000 feet for the start of next week,
but gradually rising to near 7000 feet by midweek. Meanwhile,
temperatures will gradually warm a few degrees early next week, but
still remain below normals.   Cullen


.AVIATION...Predominately VFR across the forecast area early this
morning, except for local IFR cigs along the coast. Expect fog and
low stratus to become more widespread along the coast later this
morning, with IFR/MVFR conditions possible through around 18Z. VFR
conditions continue in the interior, but there is a slight chance
for some MVFR cigs, especially along the foothills. Widespread VFR
conditions expected this afternoon, with a slight chance of TSRA
along the high Cascades. An approaching frontal system will bring
the return of MVFR cigs to the coast tonight.

KPDX AND APPROACHES...VFR expected today and tonight. Patchy MVFR
stratus possible between 13Z and 17Z, with a 15% chance of cigs
impacting the terminal. /64

.MARINE...Seas will continue to subside this morning to around 5
to 6 ft, but will remain rather choppy due to gusty northerly
winds. Speaking of the winds, expect marginal SCA gusts to
continue through daybreak. We may see some isolated SCA gusts
beyond sunrise, but these should be brief enough to not warrant
extending the current SCA.

An area of weak surface low pressure will move into the northeast
Pacific on Friday shifting the winds to the south. A series of
weak fronts look to move across the waters over the weekend which
could bring brief periods of SCA southerly gusts. Models remain in
decent agreement that a slightly stronger low pressure system
will move across the northern waters early next week. /64

PZ...Small Craft Advisory for winds until 6 AM PDT early this
     morning for Waters from Cape Shoalwater WA to Florence OR
     from 10 to 60 nm.


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This discussion is for Northwest Oregon and Southwest Washington from
the Cascade crest to 60 nautical miles offshore. The area is commonly
referred to as the forecast area. is the U.S. government's official web portal to all federal, state and local government web resources and services.