513
FXUS66 KPQR 031059
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
359 AM PDT Thu Sep 3 2026

.SYNOPSIS...Another frontal system will bring widespread rain,
breezy winds from the south, and a 20-30% chance for thunderstorms
today. Any passing thunderstorms may produce lightning, heavy
rain, gusty erratic winds, small hail, and/or a funnel cloud.
Chances for lingering showers continue through the weekend with
cooler than average temperatures. Drier conditions early next
week.

&&

.SHORT TERM...Today through Friday night...Observations over the
past 24 hours show rainfall totals across the forecast areas
around 0.30 to 0.75 inches, with higher elevations picking up
0.75 to 1.25 inches. Current radar observations this morning
shows more showers streaming into the area. So, it looks like
our region is in store for another round of widespread showers
today, with similar 24 hour rainfall totals expected.

The upper-level low which brought the rain yesterday will move
overhead of the Pacific Northwest. This will lead to cooler
temperatures aloft and a general increase in overall atmospheric
instability. Model guidance is showing CAPE values anywhere
between 100-500 J/kg across the region. This instability, along
with good lift and moisture from the overall upper-level low,
will support a 20-30% chance for thunderstorms starting late
this morning through at least tonight. Model soundings are
showing minimal shear across the region. This means that long
lived cells are not likely, which means that "storm mode" for
today will likely take the form of "pop-corn" showers and
thunderstorms. If a thunderstorm does pass over an area, it may
produce lightning, heavy downpours, gusty and erratic winds,
small hail, and/or a funnel cloud. Given that even cooler air
aloft is expected today, an isolated cold-core funnel cloud
can`t be ruled out (5-10% chance). By Friday, the upper-level
low continues to sit overhead, maintaining chances for lingering
showers and another 15-20% chance for afternoon thunderstorms.

These systems will continue to bring the first substantial
rainfall of the season. Models are still calling for 48 hour
totals (Wed morning-Fri morning) exceeding at least 1 inch of
rainfall. While this wet weather won`t be a "fire season
ender," it will definitely slow down fire season. /42-10


.LONG TERM...Saturday through Wednesday...Over the weekend, the
majority of ensemble members continue to show broad upper-level
troughing over the Pacific Northwest. However, there is uncertainty
with whether or not we remain dry or continue with lingering
showers. While 75% of ensemble members suggest showers continuing
over the region Saturday-Sunday, the other 25% keep us dry.
What we can say with higher confidence is that this upper-level
low will maintain below-average 500 mb heights and keep high
temperatures slightly cooler than average for this time of year.
Early next week, the majority of ensemble members show the
upper low weakening and beginning to move eastward. This would
favor drier conditions, but there remains uncertainty with how
much high pressure will re-build over our area, and how warm/dry
we get. /42-10

&&

.AVIATION...Through 12Z Friday...Current radar imagery as of 11Z
Thursday show showers slowly moving eastward. These showers are
currently bringing MVFR to IFR conditions to the coast. As a
result, expect these conditions to persist along the coast through
the majority of the TAF period. As for inland locations, rain
showers will gradually fill in through 14Z Thursday, along with a
mixture of VFR and MVFR conditions. Across the airspace there is a
15-40% chance of MVFR conditions at any given hour during the TAF
period. Also, any stronger showers could temporarily reduce
flight conditions to IFR or lower through 16Z Thursday. Lastly,
there is a 20-35% chance for thunderstorms across the airspace
starting around 17Z Thursday through around 03Z Friday. Any
thunderstorms that develop will have the potential to produce
lightning, small hail, and gusty/erratic winds.

Southerly winds will continue through the TAF period with gusts of
20-30 kt through 00Z Friday, with the highest gusts along the
coast. Winds will weaken beyond 00Z Friday, but still remain
mostly southerly.

KPDX AND APPROACHES...Generally VFR conditions with intermittent
MVFR conditions as showers re-develop. This is resulting in a
25-40% chance of MVFR conditions at any given hour during the TAF
period. There is a 20-35% chance for thunderstorms starting
around 18Z Thursday through around 00Z Friday. Southerly winds
will continue with gusts of 20 kt through 00Z Friday. Winds will
weaken beyond 00Z Friday, but still remain mostly southerly. /42

&&

.MARINE...Current observations show seas around 9-11 ft at 8-10
seconds with southerly gusts up to 30 kt. These conditions are
expected to continue through tonight as a fresh west/northwest
swell overnight into Thursday maintains conditions. Due to the
continued sea state and breezy winds, a Small Craft Advisory is in
effect through at least tonight. There`ll also be 15-30% chance
for thunderstorms through Thursday with the best relative chances
Thursday afternoon. Any of these storms will be capable of producing
gusty/erratic winds, small hail, and lightning.

While relatively active weather with lingering rain showers will
continue into the weekend, marine conditions will subside by
Friday with seas holding in the 4-6 ft range by Friday afternoon.
Similar conditions persist into early next week while winds
occasionally gust to 15-20 knots.

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...None.
WA...None.
PZ...Small Craft Advisory until 11 PM PDT this evening for PZZ210-
     251>253-271>273.

&&

$$

www.weather.gov/portland

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