857
FXUS66 KPQR 172140 AAA
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
240 PM PDT Tue Jun 17 2025

.SYNOPSIS...A weak cool front will bring a chance of light rain
showers to much of the area Tuesday night into Wednesday, mainly to
the north of Eugene. High pressure makes a brief return on Thursday,
bringing dry and mild conditions. Transitioning to a cool and showery
weather pattern Friday through Sunday as a closed upper level low
settles over the region and brings more substantial rain amounts to
the area. There is also a 15-20% chance of thunderstorms Friday and
Saturday. Stronger showers or thunderstorms that develop Friday into
the weekend will produce locally heavy downpours.

&&

.SHORT TERM...Now through Thursday night...High pressure beginning to
break down as the next front begins to push into the area.
Temperatures remain fairly warm today, with inland highs around 80
degrees, and the coast around low to mid 60s. Clear skies remain in
place until Tuesday evening, when clouds begin to enter the region
ahead of the front.

The incoming front late Tuesday night/Wednesday morning weakens
greatly as it moves over the coastal waters, and will be very weak by
the time it moves ashore. As such, any rain accumulation will be very
light, affecting only mostly the coast and northern Willamette
Valley/Columbia lowlands. Between 11pm Tuesday and 11pm Wednesday,
only around a 20-50% chance of exceeding 0.05 inch Portland
northwards, quickly dropping to zero south of Salem. The coast sees
slightly better chances of accumulating rain, with around 0.5-0.1
inch expected during this time. This will be accompanied by a shift
in winds to the west-northwest, with gusts up to 15-20 mph possible
Wednesday afternoon. Temperatures will also drop, with Wednesday
afternoon`s high expected to be around the low 70s inland, and around
60 at the coast.

Brief high pressure and onshore flow returns Thursday. That said,
partial cloud cover remains in the area, and temperatures are
expected to remain similar to Wednesday. However, overall dry
conditions are expected. Late Thursday night into Friday morning, the
next front begins to move in, bringing a major pattern change with
significant rain and cooler temperatures. /JLiu

.LONG TERM...Friday through Monday...The long term forecast remains
highlighted by a cool and showery weather pattern Friday through
Sunday with more significant rain amounts. Probabilities for 48-hr
rain amounts over 0.50" from 5 AM Friday to 5 AM Sunday are
approximately 50-70% for the entire area, highest at the coast, Coast
Range, and Cascades. Much cooler temperatures expected during this
period, down to the low 60s for the afternoon high inland on Friday
and Saturday.

This is in response to excellent model agreement for a cool upper
level low that will be settling directly overhead Friday into
Saturday. With this low will come cooler air aloft, helping to
steepen mid-level lapse rates. Abundant moisture will accompany this
low as well, with PWAT values likely reaching 0.8-1.0 inches by
Saturday afternoon according to the LREF grand ensemble mean. Given
enough breaks in cloud cover and subsequent surface heating, still
looking on track for enough surface-based instability to warrant
heavy downpours with any stronger showers or thunderstorms that
develop Friday and Saturday afternoon/evening. 6-hr NBM thunder
probabilities remain around 20% both Friday and Saturday.

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
fairly substantial for all locations. QPF amounts Friday through
Saturday continue to increase, currently looking to be around
0.50-0.75" for all inland locations. QPF amounts are highest over the
Cascades and foothills at 1-2 inches. Regardless of uncertainty with
exact rain amounts, confidence is high this system will bring the
highest rain totals the area has observed thus far this month. Note
the entire month of June has been dry so far, aside from June 4-5
when light rain fell over most of southwest WA and far northwest OR,
albeit missing Salem and Eugene where no measurable rain has been
observed this month. Beyond this system, most ensemble guidance
trends towards warmer and drier weather for early next week.
 -TK/JLiu

&&

.AVIATION...Visible satellite shows mostly clear skies across
the area as of 21z Tue. Expect VFR to persist at all sites
through the afternoon, with stratus returning to coastal terminals
with MVFR cigs 01-03z Wed. A weak front will approach the region
06-12z Wed, bringing the chance for light rain showers to coastal
sites starting 07-09z and inland terminals 10-12z Wed. Rainfall
amounts will be very minimal, but do expect the front to bring
MVFR cigs to inland sites through around 16-18z Wed. Conditions
will then improve back to VFR with winds shifting light westerly
behind the front towards the end of the TAF period.

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

PDX AND APPROACHES...VFR under mostly clear skies through at least
03-06z Wed. Winds increasing out of the northwest to around 8 kt
00-06z. Light rain and MVFR cigs expected with a weak front
arriving 10-12z. Conditions improving back to VFR with light west
winds and showers tapering off 16-18z Wed. /CB

&&

.MARINE...Relatively quiet conditions across the coastal waters
this afternoon as buoy observations show 10-15 kt southerly winds
and 4-5 ft seas. Light to moderate southerly breezes will persist
through tonight as the next weak frontal boundary crosses the
waters, with a few gusts to 20 kt possible overnight. Winds will
shift back to the northwest on Wednesday in the wake of the front,
remaining relatively light (5-15 kt) through early Friday as
surface high pressure builds back over the waters. Seas will will
also remain around 5 ft through the next several days, with a
modest westerly swell as the primary contributor. The arrival of
an unseasonably deep trough of low pressure will bring more
unsettled conditions from Friday into the 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.

&&

$$

www.weather.gov/portland

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