Clackamas, Oregon Weather Forecast Discussion

543
FXUS66 KPQR 192204
AFDPQR
Area Forecast Discussion
National Weather Service Portland OR
304 PM PDT Fri Sep 19 2025
.SYNOPSIS...Onshore flow will persist through the weekend and
into early next week, maintaining seasonable conditions. A
deeper trough moving in from the Gulf of Alaska will bring a
cool-down and increasing rain chances late in the weekend. The
most impactful system arrives Sunday with widespread
precipitation. A brief warm up back into the 80s for inland
locations is expected Tuesday. Confidence in the overall pattern
degrades by mid week.
&&
.SHORT TERM...Now through Saturday... Tranquil conditions persist
through Saturday under the influence of high pressure. Mostly
clear skies with north to northwesterly onshore flow expected
through tonight. A weak low over Northern California could bring
some upper level clouds to eastern Lane county through early
tonight. There is also a small (~10%) chance for an isolated
shower or thunderstorm to develop along the Cascade crest in
Lane county. Marine stratus is expected to develop and move
over the coast this evening and may slip through a gap in the
coast range and into the southern Willamette Valley briefly.
Lows expected to be around average tonight, upper 40s along the
coast and low to mid 50s inland.
Saturday is expected to remain dry and warm with highs in the
low 80s inland and 60s along the coast. Winds shift to the west
then south/southwest later in the day ahead of an approaching
cold front. Cloud cover will move in ahead of the front during
the evening.-Batz
.LONG TERM...Saturday Night through Thursday...Rain chances
increase late Saturday into Sunday as a strong shortwave trough
digs southeast from the Gulf of Alaska. The associated cold
front is expected to reach the coast around midnight Saturday
night, then progress inland reaching the Willamette Valley just
before daybreak Sunday (~5 AM). Confidence in exact timing
remains low at this time. Exact rainfall totals remain
uncertain but are generally expected to be highest across
southwest Washington and along the coast and coast range in
Oregon where 0.5-0.75 inches of rain is possible. Totals
throughout the Willamette Valley are expected to be lower
generally around 0.10-0.30 inches, higher values north to south.
The southeast portion of the CWA is expected to see the least
amount of rain, generally 0.10 inches or less due to the weak
nature and northeast to southwest orientation of the cold
front. A low- end chance (~10%) for isolated convection lingers
into Sunday morning across southwest Washington and northwest
Oregon. Temperatures Sunday will cool noticeably under cloud
cover and frontal passage, generally topping out in the low 70s
inland and 60s along the coast.
Early next week, temperatures moderate back to seasonable levels
with inland highs in the mid to upper 70s and 60s along the
coast. There is a 30-50% chance for inland highs to reach 85
again on Tuesday. Uncertainty in the pattern for the middle of
next week continues though models have backed off on
precipitation for Wednesday with PoPs topping out around 15%.
Another thing to keep an eye on will be dry and possibly windy
conditions Tuesday across the Cascades and Cascade Foothills. A
thermal trough is expected to develop across the area, setting
up offshore flow. Right now, the NBM has low a (~10-15%) chance
for RH values at or below 25% with sustained winds of 15 kts.
Confidence in the details of this set up are low at this point.
-Batz/Hall
&&
.AVIATION...High pressure aloft and low level northwesterly to
westerly winds will bring predominantly VFR conditions through
18z Saturday for inland terminals and extended periods of IFR to
LIFR conditions along the coast. The main exception to that
statement along the coast will be fog and low clouds along the
coast should push back to just offshore for most, if not all, of
the afternoon and result in a several stretch of VFR conditions
before the fog and low clouds surge back into the coastal TAF
sites between 00-03z Saturday. The marine layer appears likely to
deepen overnight, which should allow marine clouds and fog to push
farther into the Coast Range gaps overnight, but the probability
that IFR conditions reach KEUG from the southwest is 20% and KPDX
from the northwest is less than 10%.
KPDX AND APPROACHES...High pressure aloft and low level
northwesterly winds will bring predominantly VFR conditions
through 18z Saturday. There is a less than 10% chance for high
end IFR conditions briefly impacting the terminal around 15z
Saturday.
&&
.MARINE...
Northerly winds will gradually ease today with gusts
generally remaining below 20 kt. Dense fog has developed across
the inner waters this morning. This may temporarily dissipate
midday before consolidating again late this afternoon and evening
so additional dense fog advisories appear likely.
Seas are currently around 6 to 7 ft at 9-10 seconds where seas
should remain through Saturday. The next frontal system arrives
this weekend from the northwest with winds turning southerly
beginning Saturday afternoon across the waters. There is a 70-80%
chance that winds increase into Small Craft Advisory thresholds
with gusts of 25 kt Saturday night across at least the northern
waters. The strongest winds appear most likely to occur within 10
NM of the north Oregon and south Washington coast as a weak
coastal jet develops. There is a 80% chance that seas climb into
the 8-11 ft range by the end of Sunday night as a fresh swell
moves into the water.
High pressure then returns to the northeast Pacific. This will
result in northerly winds returning to the waters on Monday. A
weakening front then approaches the waters midweek.
&&
.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Dense Fog Advisory from 11 PM this evening to 11 AM PDT
     Saturday for PZZ210.
     Small Craft Advisory from 11 PM Saturday to 8 AM PDT Sunday
     for PZZ210.
     Dense Fog Advisory until 11 AM PDT Saturday for PZZ251>253.
     Small Craft Advisory from 8 PM Saturday to 6 AM PDT Sunday for
     PZZ251-271.
&&
$$
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NWS PQR Office Area Forecast Discussion