998
FXUS66 KPQR 182200
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
300 PM PDT Fri Jul 18 2025

.SYNOPSIS...Strengthening onshore flow will bring continued
cooling through the weekend with temperatures falling before
normal to begin the next workweek. An upper low passing overhead
Sunday night into Monday may bring the best chances for rain so
far this month, although odds for accumulating precipitation
remain fairly low. Forecast confidence decreases midweek,
although a return to warmer temperatures is most likely.

&&

.SHORT TERM...Now through Sunday...Another upper-level shortwave
passing over or just north of the region this afternoon and
evening will usher in intensified onshore flow, continuing the
cooling trend through the weekend. Mid-level temperatures around
15C at 850 hPa today will fall to 10-11C by Sunday afternoon,
pushing surface temperatures below seasonal normals, with
afternoon highs falling to the 60s along the coast and in
terrain, and mid 70s to low 80s along the I-5/I-84 corridors.
The stronger onshore push will also favor increased low cloud
cover, especially along the coast and into Coast Range gaps,
including up the Columbia River into the Portland/Vancouver
metro. Coastal mist and fog are also most likely Sunday morning
reaching into west-facing Coast Range valleys. West to northwest
winds will also strengthen modestly, with gusts as high as
30-35 mph through the Columbia Gorge each afternoon. -Picard


.LONG TERM...Sunday Night through Friday...By Sunday night into
Monday, there is increasing consensus that a vigorous upper
shortwave will dive southward over the Haida Gwaii and
Vancouver Island, resulting in elongated upper troughing or even
a cutoff low centered developing over the Pacific NW. While
this wave may support light rain reaching into the region to
start the workweek, chances remain fairly low, only 15-25% along
the coast and in the Coast Range, and slightly lower in the
Cascades and foothills. It`s worth noting that an increased
number of global ensemble members are showing accumulating rain
as well as anomalously high values of precipitable water,
generally 1-1.25" across the forecast area, which would be above
the 90th climatological percentile of KSLE sounding observations.
With light mean cloud-level winds, around 5 kt, slow-moving
convective showers which could wring out a true wetting rain in
some areas cannot be ruled out.

Numerical guidance then diverges toward the middle of the week
as the evolution of the trough or cutoff low remains somewhat
low confidence. Many ensemble members are continuing to favor
another cutoff upper low developing near Cape Mendocino while
the mean flow to the north returns to a more zonal pattern. In
this scenario, heights rising aloft and moderating mid-level
temperatures would favor a warming trend at the surface, while
southerly to southeasterly flow about the eastern flank of the
upper low could generate convection over the Cascades. -Picard

&&

.AVIATION...Inland, VFR conditions are expected beneath
increasing cirrus clouds at or above 25 kft through this
evening. A stronger marine push may result in few-sct low
stratus reaching up the Columbia River to Portland-area
terminals (KPDX, KHIO, KVUO, KTTD), but sufficient coverage to
yield MVFR cigs is unlikely, only a 10-20% chance after 12-15z
Sat. At the coast, expect low marine stratus with high-end IFR
to low-end MVFR cigs to persist at KAST through 00z Sunday.
Forecast cigs are a bit more uncertain at KONP. Although KONP
was mostly clear as of 2130z Friday, low marine stratus will
eventually move back in this evening, however the exact onset
timing is uncertain and could occur anywhere between 00-05z
Saturday. Given the stronger marine push this evening, suspect
timing will be closer to 00z rather than to 05z.

Diurnal west to northwest winds build to 5-10 kt with occasional
gusts of 15-20 kt this afternoon, then diminish to 5 kt or less
tonight.

PDX AND APPROACHES...Continued VFR conditions expected through
the period. High cirrus coverage increases through this
afternoon, then scattered low clouds develop overnight as a
stronger marine push takes place. There is a 10-20% chance for
sufficient stratus coverage to yield MVFR cigs after 12-15z Sat
before stratus mixes out by 18z Sat. Northwest winds remain
around 10 kt this afternoon with gusts up to 15-20 kt, before
easing to 5 kt or less after 06z Sat. -TK/Picard

&&

.MARINE...While winds remain weak across the waters, high
pressure will maintain northerly to northwesterly winds through
next week, however winds will remain relatively weak and should
stay under 10-15 kt. Seas should subside to 5 to 6 ft Friday
evening and then stay at or below 5 ft through the upcoming
week. There are no signs conditions will meet Small Craft
Advisory criteria over the coastal waters at this time. -TK

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

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

&&

$$

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