Area Forecast Discussion
Issued by NWS Portland, OR
FXUS66 KPQR 260418
Area Forecast Discussion
National Weather Service Portland Oregon
917 PM PDT Sun Sep 25 2016
.SYNOPSIS...A strong early autumn upper ridge over the northeast
Pacific and the Pacific Northwest today will slowly move eastward
tonight and Monday, continuing to produce mild and dry weather over
southwest Washington and northwest Oregon through Monday. A weak
front will brush the forecast area Monday night and Tuesday for more
clouds, onshore flow, and spotty light precipitation mainly near the
coast. The forecast area will be in between systems during the mid
week period. The next low is expected to affect the area later in the
week and on next weekend.
.SHORT TERM...(Tonight through Wednesday)...No changes. Previous
discussion follows...A strong upper level ridge over the Pacific
Northwest today will slowly move eastward tonight and Monday. The net
result will be plenty of sunshine during the days through Monday.
Tonight will be mostly clear, Monday will be warm again with temps 10
degrees or possibly more above normal especially inland, and just
some patchy late night and morning fog tonight and Monday morning.
We have been seeing light offshore flow today under the upper ridge.
The models show a surface thermal trough building along the coast
tonight that will lead to some very modest east wind through the
Gorge late tonight and for a while on Monday. This should lead to
Monday being the warmest of the week.
After that, things change as a weak system approaches and moves onto
the coast Monday night and onshore early Tuesday. This will cause
clouds to increase along the coast Monday night and Tuesday with a
little drizzle or light rain, and for clouds to spread inland late
Monday night and especially Tuesday morning. Could see some patchy
drizzle inland around the Columbia River Tuesday morning. The onshore
flow should drop temperatures back to around normal on Tuesday. The
models indicate the clouds should break up some Tuesday afternoon,
with afternoon highs closer to seasonal normals, that is in the lower
to mid 70s.
Clouds continue to break up Tuesday night and Wednesday as we are in
between systems. Southwest flow aloft should keep some marine layer
going along the coast for at least some night and morning fog or low
clouds. Inland looks as though any morning clouds or fog will be
patchier with a decent amount of sunshine during the day. Temps
should be a little above normal. Tolleson
.LONG TERM...(Wednesday night through Sunday)...Onshore flow will
persist for the middle of the week, maintaining temperatures at to
slightly below seasonal normals. Clouds increase over the region
Friday with a upper level trough sliding south over the far
northeastern Pacific late Thursday and Friday. Several impulses
rotating around the upper low will bring a few rounds of
precipitation late Friday through Sunday. Slight timing differences
remain in the forecast model depictions of the impulses, so have
continued the period of generally higher PoPs late Friday through
the weekend, though it remains possible that there might be a short
period of a break in precipitation at some point over the weekend.
The upper low eventually pushes onshore into the Pacific Northwest
later Sunday before moving into the Great Basin. As a result,
temperatures look to be well below normal - only reaching the lower
60s inland - next weekend. With the colder air mass in place, snow
levels should lower to around 5,500 feet by Sunday, low enough to
bring some snow to the higher elevations of the Cascades. Cullen
.AVIATION...VFR conditions with dry n-ne winds tonight through
Monday morning. Do not expect much fog to develop late tonight. Any
fog that does form will be shallow and clear quickly Mon morning.
Winds will become more onshore Monday afternoon and evening with
marine stratus returning Monday night.
KPDX AND APPROACHES...VFR conditions with light winds through
Monday morning. expected the next 24 hours. Northerly winds will
become light overnight. East winds near the Gorge should prevent
fog/low stratus development Mon morning. /64
.MARINE...The thermal trough is weakening over the waters
allowing north winds to ease a bit. North gusts have eased below
25 kt, and have cancelled the small craft advisory for winds. The
thermal trough will continue to weaken Monday and move inland
Monday afternoon and evening for northwest winds and high pressure
over the coastal waters. High pressure strengthens Tuesday and
north winds will likely increase to around 25 kt. Wind driven seas
will increase Tuesday and boost seas to around 8 ft. Otherwise the
seas will be 5 to 6 ft. TJ
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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.