Area Forecast Discussion
Issued by NWS Portland, OR

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXUS66 KPQR 222324 AAA
AFDPQR

Area Forecast Discussion...UPDATED
National Weather Service Portland OR
425 PM PDT Sun Oct 22 2017

Updated hazard section...removed hydrology section

.SYNOPSIS...Decreasing showers through tonight. Then High pressure
builds over the region, with dry weather for much of the coming week.
Exception will be some threat of showers Wed/Wed night. Otherwise,
dry, with mild days and coolish nights, along with areas of late
night/morning fog and low clouds. Bit stronger offshore flow later in
the week may well keep most areas fog free.
&&

.SHORT TERM...Tonight through Tuesday...Westerly flow aloft over the
region, with variable clouds over the region. Air mass not all that
much colder, so shower activity is not all that widespread or
organized. Will keep scattered showers this evening for most areas,
with decreasing trend overnight. With the westerly flow, showers will
be most common against the Cascades, and to some degree, over the
Coast Range and Willapa Hills. Snow levels remain well above the
passes, generally 7000 to 8000 feet.

High pressure will build over the region later tonight, and
especially Mon. This will end the shower threat overnight. But with
breaks in the cloud cover, and moist ground with light winds, will
see fog/low clouds form later tonight, with most it being most
extensive between 5 am and 10 am Mon. Would not be surprised to see
locally dense fog as well. Extent and timing of onset of fog will
depend lot on how much the higher clouds break.

Once the cloud clouds/fog dissipates later Mon am, will see sunshine
and mild temperatures across much the region.  Will trend light
offshore Mon night through Tue. Think may be enough to keep fog
patchy at worst along the coast, but still areas of fog and low
clouds for interior valleys. Again, like Monday, fog/low clouds will
dissipate later Tue am, leaving region sunny and mild. Rockey.

.LONG TERM...Tuesday night through Saturday...No changes. Previous
forecasts is as follows:  Strong ridge of high pressure will buckle
slightly Wednesday, allowing the tail end of a cold front to clip
mainly our northern zones with a chance for showers. Models show
decent agreement that we will otherwise be dry through Saturday as a
strong upper ridge builds over the NE Pacific and Pacific Northwest.
Given all the rain we have had this weekend, there will be plenty of
ground moisture for fog in the valleys. This may cause some
challenges regarding sky cover and temperatures later in the week as
valley inversions become established. Strengthening inversions may
also result in air quality and stagnation issues later this week.
Cooler air east of the Cascades may support high pressure there and
east winds through the Gorge, which would tend to limit the fog and
air stagnation issues in the Portland metro area, but it is difficult
to tell these details this far out in time.  Weagle.
&&

.AVIATION...VFR prevailing with scattered showers this afternoon
and evening. High pressure will build over the area overnight and
clouds will thin. This will lead to a mixture of fog and low
stratus late tonight and Mon morning. Fog will probably have less
coverage than stratus, but expect areas of low MVFR to IFR
conditions.

KPDX AND APPROACHES...VFR prevailing with scattered showers.
Showers end this evening with fog or low stratus developing
overnight with low MVFR to IFR conditions expected Mon morning.
&&

.MARINE...Winds continue to ease this afternoon, but showers
bringing some gusts to near 20 kt. Winds will continue to
decrease tonight as high pressure builds over the waters and
inland. High pressure remains through the first part of this
week. An inverted surface trough along the coast strengthens Mon
night and Tue, which will produce northerly wind gusts around
20-25 kt. This will be short lived as a weak cold front drops
south into our waters on Wed, bringing moderate small craft
northerlies behind this feature. The inverted surface trough
under high pressure returns late in the week with small craft
advisory wind speeds possible.

Seas in the 12 to 14 ft range this afternoon will slowly subside
to below 10 ft late Mon afternoon or evening. With dominant wave
periods still around 12 seconds, seas will continue to be steep.
From Tue through Fri seas remain in the 6 to 9 ft range.
&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory for hazardous seas through Monday
evening on all coastal waters.
     Small Craft Advisory for Rough Columbia River Bar
tonight through 9 am Monday.

&&

$$

Interact with us via social media:
www.facebook.com/NWSPortland
www.twitter.com/NWSPortland

This discussion is for Northwest Oregon and Southwest Washington
from the Cascade crest to 60 nautical miles offshore. This area is
commonly referred to as the forecast area.


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.