Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 181623 AAA
AFDPQR

Area Forecast Discussion...Updated
National Weather Service Portland OR
923 AM PDT Wed Jul 18 2018

Updated aviation discussion.

.SYNOPSIS...Gradual cooling is expected in the interior each day
through the end of the week as onshore winds and a deepening marine
layer increase the marine influence. An upper ridge builds over the
weekend with inland temperatures warming back into the 90s next week.

&&

.SHORT TERM...Today through Friday...Satellite imagery this morning
shows stratus along the coast, pushing inland so far to Troutdale and
now backbuilding to PDX as well as moving south along the Cascade
foothills. LAPS surface analysis shows the surface ridge axis around
PDX, which likely explains why clouds have been slow to backbuild and
push south. There may not end up being much cloud cover south of the
PDX unless the ridge axis shifts south.

Even without cloud cover across the entire area, still expect
temperatures to be a bit cooler today than yesterday due to stronger
onshore flow and inland spread of marine air. Overnight temperatures
have been trending 5 to 10 degrees cooler than the same times last
night. Eugene, for example, was down to 56 degrees at 2 AM, a full 7
degrees cooler than 24 hours earlier, despite current light offshore
flow. Lowered afternoon temperatures for today in areas which will
see clouds as they may be slow to clear. Overall, expect temperatures
to peak in the 80s inland, lower north and higher south.

An weak upper trough tonight and Thursday along with a further south
surface ridge axis will assist the marine layer and stratus in
pushing further inland into Thursday morning. With 500 mb heights
slightly lower Thursday and the additional morning clouds, expect
temperatures Thursday to be a few degrees cooler than Wednesday,
particularly in areas which don`t see clouds Wednesday.

A closed upper low drops south from the Gulf of Alaska into British
Columbia Thursday night and Friday, sustaining a deep marine layer,
inland clouds, and slightly cooler afternoon temperatures. This will
likely be the coolest day of the week with the temperatures in the
Willamette Valley peaking in the upper 70s to low 80s. Bowen

.LONG TERM...Friday night through Wednesday...The upper low passes to
the north Saturday with a lobe of energy dropping south over the
local area. This sounds like it should mean that Saturday`s high
temperatures inland are similar to Friday`s but weakening onshore
flow will likely mean temperatures a little bit warmer Saturday.
However, the ECMWF has a particularly energetic lobe dropping south,
which would keep temperatures a little bit cooler. For now have gone
with mid 80s.

Both the GFS and ECMWF show heights increasing Sunday for warmer
temperatures. 850 mb temperatures around 20 C should translate to
inland valley temperatures back up around 90 F again. From there,
ridging takes hold again for what looks like another hot week. Upped
temperatures slightly more on Monday, now mid to upper 90s in the
Willamette Valley. Low temperatures Monday night also look rather
warm, with another almost equally hot day Tuesday, so expect the
Monday-Tuesday time frame to create some potential heat issues. There
are slight differences between the models Wednesday, but the only
real question would be whether temperatures are in the low 90s or the
mid to upper 90s - either way it look like continued heat. Bowen

&&

.AVIATION...We will continue to see a mixture of flight conditions
across the forecast area this morning. MVFR stratus in the interior
will linger for the next couple of hours and is expected to lift and
scatter between 18-21Z. VFR conditions is then expected through
tonight, with MVFR conditions possible north of KSLE early Thursday
morning. The south Willamette Valley may see a few hours of MVFR
stratus Thursday morning, but confidence is lower.

The coast will likely see some clearing today, especially south of
KTMK. KONP may see brief periods of reduced flight conditions this
morning, but should remain mostly VFR through this evening. KAST
will be slower to improve today, but a few hours of VFR conditions
are likely this afternoon. IFR stratus looks to start redeveloping
after 03Z this evening, with widespread IFR conditions expected
after midnight tonight.

PDX AND APPROACHES...MVFR stratus will linger through the morning
hours. Expect stratus to lift and scatter between 18-20Z, with VFR
conditions through tonight. MVFR stratus looks to return by early
Thursday morning. /64

&&

.MARINE...High pressure over the northeast Pacific and thermal
low pressure over southwestern Oregon will result in a fairly
typical summer-time northerly wind pattern for much of the next
week. Winds should strengthen a bit Wednesday across the central
Oregon waters and even more so on Thursday with plenty of gusts
to 25 kt during the afternoon and evening hours. Expect more of
the same on Friday and Saturday. Seas will likely climb into
steep and hazardous Small Craft Advisory criteria of 7 to 8 ft
with a dominant period of 6 to 8 seconds Thursday and Friday.
Winds and seas should ease a bit late in the weekend and early
next week as thermal low pressure over southern Oregon shifts
north and inland. /Neuman

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory for winds from 2 PM this afternoon to 11
     PM PDT Friday for Coastal Waters from Cascade Head OR to
     Florence OR out 60 NM.

&&

$$

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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 CWA or forecast area.


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