Area Forecast Discussion
Issued by NWS Portland, OR
FXUS66 KPQR 212057
Area Forecast Discussion
National Weather Service Portland Oregon
156 PM PDT Fri Oct 21 2016
.SYNOPSIS...The remains of the front that brought rain to southwest
Washington and northwest Oregon Thursday persisted over the southeast
part of the forecast area this morning but will continue to weaken
and dry out the remainder of today. An area of showers associated
with an offshore upper level low will reach the coast this afternoon,
spreading some showers inland later today and this evening especially
from about Salem northward. The next decent front will spread more
rain onshore and inland Saturday night and Sunday, followed by
another front late Sunday night and Monday. A broad area of low
pressure will remain off the coast and continue to produce unsettled
weather at times in southwest Washington and northwest Oregon next
.SHORT TERM...Tonight through Monday...Precipitation in the Oregon
Cascades along the remains of the front from Thursday will continue
to decrease the remainder of this afternoon and early evening.
Showers have increased near the coast this afternoon as a disturbance
at the leading edge of the cooler air associated with an offshore low
begins to move onshore, and this is expected to move into the
forecast area the remainder of this afternoon and evening. The
greatest coverage of showers will be along the coast especially
north, and in the northern valleys. There is a chance of thunder
along the north coast today and into the Kelso area late this
afternoon and evening, but probably not much farther south or east.
We will be in between systems later tonight and most of Saturday with
just a few residual showers if that. Under these somewhat stable
conditions we will probably see more areas of fog and low clouds
later tonight and Saturday morning than we saw this morning.
The next pretty decent front is expected to approach the coast late
Saturday and move onshore overnight Saturday night and early Sunday.
The front weakens some as it moves inland, but should give a decent
amount of rain to most areas. This front will also weaken
considerably with decreasing precipitation as we go through Sunday
Another stronger front approaches the coast late Sunday night and
moves inland during the day Monday with another good shot of rain.
Snow levels in the Cascades may fall to near Timberline Lodge on
.LONG TERM...(Monday night through Friday)...Much uncertainty in the
extended, as the models diverge significantly later next week. A
broad low pressure system remains off the Coast of Washington and
Oregon through the first half of next week. The front associated
with the occlusion of the Low moves through on Monday bringing rain
across the area. Tuesday is when the models start to diverge
significantly. The GFS brings a shortwave up the Coast bringing
another round of moderate to heavier rainfall on Tuesday night into
early Wednesday. The ECMWF is slower bringing this system up the
Coast, keeping us mostly dry on Tuesday, except some light rain
along the Coast. This model brings the midweek system through on
Wednesday into Thursday. Beyond midweek, there appears to be either
a cutoff system that sets up a rex-block pattern through the end of
the week, or a broad upper-level trough that keeps us rainy into
next weekend. If the rex block sets up, we could be dry into next
weekend. So essentially, flip a coin for whether it will be wet or
dry going into next weekend. Snow levels this week are expected to
stay up above 6000 feet, so snow should not be an issue if your
traveling across the passes this week. -McCoy
.AVIATION...As usual with increasing mid/high clouds, as any low
stratus/fog is often much slower to break up. Mostly VFR across
region, but still lot of areas with MVFR cigs from n Willamette
Valley northward through Cowlitz Valley. A weak front will
continue to break apart as it moves inland this evening. Front
will drag MVFR cigs inland through the evening. Still looks like
front will push most of the low level clouds out of the region
later tonight. But with better potential of clearing and a
generally moist air mass still in place, should see widespread
fog and low stratus later tonight, and persisting well into Sat.
KPDX AND APPROACHES...generally VFR into this evening, but still
have pockets of MVFR cigs in and around metro. But not expecting
to persist over the ops area. A weak front will move over area
later this evening with MVFR returning. Rain threat diminishes
rapidly after 1 am, with clouds breaking up. More extensive IFR
stratus/fog after 10z, persisting will into Sat. rockey.
.MARINE...Winds are southerly at 15 kt or less. A weak cold front
will move through the waters through early evening, but not much
in way of any boosted winds. Westerly swell will build up a bit
later tonight. Buoy 5 now at 19 ft, and decaying that swell to the
coast would put 13 to 15 ft swell across the coastal waters. So,
will boost swell heights up a bit for later tonight into Sat am.
A stronger frontal system will arrive late Sat. Expect at least
solid small craft winds from later Sat afternoon through early
Sun AM, with the potential for gusts 30 to 35 kt. For now, will
leave a solid small craft advisory event for that time frame.
Afterwards, the series of stronger fronts continue, with each new
front arriving about every 24 hrs through early next week.
PZ...Small Craft Advisory for hazardous seas from on all coastal
waters for tonight through Sat evening.
Small Craft Advisory for winds on all coastal waters for
late Saturday afternoon through Saturday night.
Small Craft Advisory for Rough Columbia River Bar from
6 PM this evening to 6 PM Saturday.
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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.