356
FXUS66 KPQR 182205 AAA
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
301 PM PDT Wed Jun 18 2025

.SYNOPSIS...A weak cold front will bring light showers today,
mainly along the coast and Coast Range with mostly dry
conditions inland. Dry weather prevails on Thursday. Friday to
Saturday, a low pressure system will return widespread rain to
the area. This system will also lead to a 15-20% chance for
thunderstorms on Friday, which could produce lightning, heavy
downpours, and gusty outflow winds. Drier and warmer weather
returns Sunday into early next week.

&&

.SHORT TERM...Now through Thursday night...Showers are weakening
throughout the region, and any remaining weak rain showers will end
by 5-6pm Wed. Afterwards, dryer conditions expected Thursday as brief
high pressure builds into the region. Temperatures will be fairly
similar on Thursday compared to today, with inland high temperatures
around the low 70s. The coast sees high temperatures closer to 60.
Winds through the Columbia River Gorge on Thursday will also be
somewhat elevated, with 20-25mph westerly gusts possible Thursday
afternoon.

Cloud cover will gradually increase ahead of the next system late
Thursday night into Friday morning. From Friday onwards, a major
pattern change is expected, bringing significant rainfall to the
area. Further details in the following long term discussion. /JLiu

&&

.LONG TERM...Friday through Tuesday...Very high confidence
for much cooler and wetter weather across northwest Oregon and
southwest Washington at the end of the week, beginning Friday. Upper
level trough dipping down into the Pacific Northwest from the
northeast Pacific at that time, with temperatures dropping on Friday
and Saturday, with highs forecast to peak in the upper 50s to low
60s across interior lowland valleys on Friday and Saturday.

The initial surface cold front associated with the upper level
trough will arrive on Friday, returning widespread showers. A
secondary shortwave will then arrive on Saturday as the upper
level low moves directly overhead, continuing the wet weather.
Will note that there is a 15-20% chance for thunderstorms Friday
afternoon. Cold air aloft from the trough will increase
atmospheric instability and steepen lapse rates. Combined with
abundant moisture and lift, this will be favorable for the
development of thunderstorms or heavy showers. Any passing
thunderstorms could produce lightning, downpours, or gusty
outflow winds. When thunder roars, go indoors! Saturday could also
see some thunderstorms in the afternoon, but chance has come down
somewhat compared to yesterday due to stronger cloud cover. Only
around 5-10% chance Saturday afternoon and evening.

The bulk of the precipitation is forecast from early Friday
morning to early Sunday morning. A soaking rain is likely, as
48-hour probabilities for 0.50" of rain or more from 5 AM Friday
to 5 AM Sunday is around 50-70% for interior lowland valleys and
70-90% along the coast and high terrain. For 1" or more of rain
in 48 hours during this same time period, probabilities are
around 15-20% for interior lowland valleys and 30-50% along the
coast and high terrain. The current rainfall forecast calls for
0.50-0.75" across the Willamette Valley and southwest Washington
lowlands, 0.75-1.25" along the coast and Coast Range, and
0.75-2" across the Cascades. Given the showery nature of
precipitation this weekend, some locations will significantly
overperform for total rain amounts while other locations
underperform. That said, forecast rain amounts are still fairly
substantial for all locations for this time of year.

Dry weather returns on Sunday as high pressure re-builds. High
pressure will continue heading into early next week, leading to
sunnier and warmer conditions. Temperatures will rebound, with
NBM guidance suggesting a 60-80% chance that temperatures
exceed 80 degrees across the Willamette Valley by Monday and
Tuesday.       -Alviz/JLiu

&&

.AVIATION...Visible satellite shows low clouds continuing to
scatter out west of the Cascades as a weak front departs the area,
promoting mainly VFR conditions as of 21z Wed. Models depict a
60-80% chance for low clouds and MVFR conditions to redevelop
along the northern coast including KAST around 12z Thu, with
a 30-50% chance along the central OR Coast including KONP. Expect
inland terminals to remain VFR through the rest of the period.
Northwest winds increasing to 8-12 kt 22-01z, then diminishing
below 5 kt after 06z Thu.

*KTTD ASOS is currently INOP except for altimeter and will be AMD
 NOT SKED.

PDX AND APPROACHES...VFR conditions with cigs above FL040 through
the period. West winds around 8 kt shifting NW around 10 kt after
00z Thu. Winds then diminishing near or below 5 kt after 08z Thu.
/CB

&&

.MARINE...Relatively quiet conditions persist across the coastal
waters this afternoon as buoy observations show 5-10 kt west
winds and 3-5 ft seas in the wake of this morning`s front.
Winds will turn more northwesterly or even northerly on Thursday
but will remain in the 5-15 kt range as weak surface high
pressure builds offshore. Seas will build to around 5-6 ft on
Thursday, with a modest westerly swell as the primary contributor.
The arrival of an unseasonably deep trough of low pressure will
bring more unsettled conditions and a chance of thunderstorms
Friday into this weekend, with winds increasing closer to small
craft criteria and seas building to 7-8 feet by Saturday. /CB

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...None.
WA...None.
PZ...None.

&&

$$

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