311
FXUS66 KPQR 281651 AAA
AFDPQR

Area Forecast Discussion...UPDATED
National Weather Service Portland OR
950 AM PDT Thu Aug 28 2025

Updated aviation discussion.

.SYNOPSIS...The active weather from the last several days has
passed, and a typical summer pattern is moving in. Low pressure
sits to the north over Washington, with another area of low
pressure over the northeast Pacific. Ridging over the next two
days will lead to warmer temperatures and drier conditions. The
Pacific low pushes inland over the weekend cooling things down
and increasing moisture. Drying and warming next week.

&&

.SHORT TERM...Now through Saturday...After the last few days of
being woken up each night by thunderstorms, drier conditions
are on the way. This morning, satellite imagery shows a weak
low spinning over the OR/WA border and a stronger low over the
northeast Pacific. This inland low is wrapped in clouds and
monsoonal moisture but most of that is staying well to the
north. Unlike last evening, rain showers are generally missing
the forecast area with the majority of the area dry with minimal
cloud cover. Through the day the low will continue to slowly
shift northward with an inverted trough forming at the surface.
Dry air will wrap over the area causing humidity to drop and
skies to stay cloudless. Warmer air will also move in aloft with
850 mb temperatures around 16C. With increased daytime heating,
looking at temperatures rising into the upper 80s to near 90F
inland. Because of persistent onshore flow and cloud cover, the
coast will see little fluctuation in highs today where they
will reach the mid-60s. Winds will generally be onshore with a
northerly component in the Willamette Valley. Minimal change on
Friday as the overall pattern remains unchanged.

By Saturday the low in the northeast Pacific will near the
coastline. Overall, ensembles are in good agreement with the
timing and track of this low on Saturday but the sensible
weather associated with it still is unclear. Some models suggest
a wetter solution while others show a trend towards a dry
anomaly. Looking at this system though, it is beginning to fill
as it approaches and will stall in a position where
precipitation will be isolated and concentrated to the north and
right along the coast. Temperatures too will drop to near
seasonable highs. In combination with this low, a ridge will
form over the inner- mountain west . As that ridge amplifies and
the low nears the Pacific Northwest, the pressure gradient will
increase with gusty westerly winds expected. These winds will
generally impact the Columbia River Gorge, Upper Hood River
Valley and the gaps of the Coast Range. -Muessle


.LONG TERM...Sunday through Wednesday...Overall will see minimal
change in the forecast between Saturday and Monday as the low
sits nearly stationary along the north Oregon and south
Washington coast. Synoptically though there is one change which
will come into play later in the week. A deepening area of low
pressure is forming over the Dakotas on Sunday and thus will
create a omega-block type pattern. While not necessarily a true
blocking pattern, the two features will aid in building the
ridge stretching from eastern Oregon to Montana. This feature
will cause temperatures to rise. Highs will range anywhere from
80-90F in the Willamette Valley, the 70s along the Cascades, and
the upper-60s along the coast, and rise a few more degrees on
Tuesday. Overnight temperatures on Tuesday into Wednesday
morning will be elevated so some may experience difficulty
getting relief from the heat.

Now, as we move into Wednesday and Thursday prepare for a little
meteorological mess. Let`s look at the features we have
mentioned and what their status may be. The low in the northeast
Pacific: moving north over Vancouver Island. The low over the
northern plains: dissipating. A tropical system over southern
California...that one is new. This system will be a stronger
area of low pressure slowly advecting inland. This low will
throw a wrench into the system and thus creating a high
uncertainty forecast. The impact of types of storms on northern
patterns generally are not handled well by models but typically
cause ridging to amplify. However, the low in the northeast
Pacific will be lingering nearby. The level of uncertainty and
inconsistency in ensemble models is exceptionally high. For
example, on Wednesday in Portland the NBM high temperatures
range from 76-105F (10th to 90th percentile), and the global
ensembles have a range of 81-99F. The story is similar on
Thursday with a wide swath of temperatures, a mixture of
locations for the low, and everything in between. Ultimately,
there is so much uncertainty at this point that the long term
forecast will change in the coming days. -Muessle

&&

.AVIATION...Expect VFR conditions and mostly clear skies for
inland terminals through the TAF period. That said, there is a
20-25% chance for MVFR cigs below 3000 ft at KEUG and KSLE between
12-18z Friday. In addition, there is a 25-35% chance for MVFR
cigs at KHIO, KPDX, KUAO and KTTD during that same time. These
probabilities are not high enough to reflect MVFR cigs in the TAFs,
however amendments may be needed if observations suggest stratus
will push inland. Coastal terminals will see much different
conditions, but similar to the last few days. Expect LIFR/IFR
conditions at coastal terminals through most of the TAF period,
with best chances for improving out of LIFR morning stratus
between 18-23Z Thursday (Chances to improve to VFR: 50-60% chance
at KAST, 20-30% chance at KONP). Winds are generally light at
around 5 kt or less for all terminals, but should increase
slightly to around 7-8 kt out of the west at KSLE and KEUG towards
23-01z as a sea breeze pushes inland.

PDX AND APPROACHES...VFR conditions will continue with mostly clear
skies and light northwesterly winds through the TAF period. -TK

&&

.MARINE...Benign conditions are expected into early next week
with winds below 10 kt and seas 2-4 feet. Winds become southerly
this morning in response to weak low pressure over the coastal
waters drifting northward, however wind gusts should stay below
10-15 kt. Winds shift back to northerly by Sunday. Both winds and
seas are forecast to stay below Small Craft Advisory criteria at
least until early next week. Could see gustier winds in the
middle of next week, but look to still remain below Small Craft
Advisory criteria. ~Hall/Batz

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

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

&&

$$

www.weather.gov/portland

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