669
FXUS66 KPQR 252340
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
440 PM PDT Fri Apr 25 2025

.SYNOPSIS...Upper level low over northern California will shift
east through the evening into Saturday. The position is
increasing southeasterly flow ushering in moisture aloft.
General onshore flow will continue through mid week despite a
ridge of high pressure forming Monday. Another short wave moves
in on Tuesday with another chance for precipitation.

&&

.SHORT TERM...Now through Monday Night...Clouds are beginning
to dissipate in the northern portions of the forecast area while
the southern potions remain under dense cloud cover. These
clouds have been an inhibiting factor to significant daytime
heating like we saw yesterday. However, where skies have
cleared, seeing about a degree an hour of warming. To the south,
a low aloft is spinning over Northern California. This low
continues to be the main weather maker today as it encourages
southeasterly flow and wrap around moisture. While radar has
showed showers throughout the area, accumulation has been
minimal. This is mainly due to the significant amount of dry air
right at the surface and above 5000 ft. The precipitation has
had the opportunity to evaporate before reaching the ground
(this is called virga).

Overnight the low will shift east slowly which will enhance the
precipitation potential more. Based on high resolution models,
there is good consensus in precipitation falling along eastern
Lane and Linn counties through Saturday morning. Accumulation
expected to be highest along the lee side of the Cascades.
Because conditions will be showery, exact accumulation is
difficult to narrow down. Under stronger showers where the
atmosphere is moist enough, precipitation will be higher. In
contrast, there are many areas that will see little to no
accumulation. In addition to the precipitation, the east-west
pressure gradient will reach around 10 mb. Expect gusty
westerly winds through the Gorge, especially in the Upper Hood
River Valley.

Onshore flow persists through the week which will keep
temperatures moderated. -Muessle

.LONG TERM...Tuesday through Friday...The weak ridge will break
down on Tuesday as a eroding shortwave trough advects inland
from the Northeast Pacific. This shortwave will produce more
widespread showers over southwest Washington and northwest
Oregon. This is a fairly fast moving system. Humidity between
850-250 mb will dry significantly which can be observed in
soundings from the area. This will lead to lower humidity along
the mountains and clear skies. On Wednesday, the ridge will
intensify and a thermal trough will form along the coast. Winds
aloft (above 850 mb) will transition to the northeast bringing
in warmer air from east of the Cascades. In the afternoon the
trough will shift east of the Cascades, then back to the west
side in the evening.

The Willamette Valley temperature forecast has fairly good
agreement in the long term. The warmest of the next week will
be Thursday (when the ridge is at it`s peak). The NBM shows a
high temperature range in Eugene of 76-80 degrees F. Along the
coast, that range is in the upper 60s. Will mention though that
the potential downsloping effects off of the coast range could
cause temperatures to be higher around Tillamook. In fact, in
Hood River, the forecast is showing the 25th-75th percentile of
temperatures at 80-82 degrees F which is incredibly narrow.
-Muessle

&&

.AVIATION...VFR flying conditions beneath largely clear skies
are widespread across inland terminals this afternoon, aside
from increased low cloud coverage at EUG. A weak low over
northern California will continue to support clouds and light
rain showers across southern areas, although no impacts from
rain are expected at area terminals. MVFR cigs are likely
(60-80% confidence) at EUG overnight from 09Z through 20-22Z
Sat. Elsewhere inland, a shorter duration of MVFR cigs is
favored, with 40-60% confidence of cloud bases at 2-3 kft from
10-12Z through 16-18Z Sat. Flying conditions improve by Saturday
afternoon, with clearing skies expected after 18-21Z Sat. Winds
of less than 10 kt out of the northwest to southwest are favored
through the period.

Along the coast, persistent marine stratus will see current MVFR
cigs lower to IFR after 02-03Z Sat with 50-70% confidence. IFR
or low-MVFR cigs will continue into the overnight period, with
MVFR conditions favored after 10-15Z Sat as cigs trend upward.
Cigs will further lift with some clearing expected into Saturday
afternoon, with cloud bases trending toward VFR after 21-22Z Sat.
West to northwest winds at 5-10 kt overnight will increase to
10-15 kt with gusts to 20 kt out of the northwest after 21Z Sat.

PDX AND APPROACHES...VFR conditions expected to continue through
this evening and tonight beneath largely clear skies. Clouds will
increase overnight, with a 50% chance of MVFR cigs at 2-3 kft
after 12Z Sat, continuing through mid-morning. VFR conditions will
again be favored by 16-18Z Sat as low clouds dissipate. No vis
restrictions are anticipated throughout the period. Winds continue
around 5 kt out of the northwest to southwest overnight, increasing
to 5-10 kt out of the west to northwest after 16-18Z Sat. -Picard

&&

.MARINE...Winds gradually shifting northwest through this
afternoon, with wind speeds increasing by tonight. Gusts may
approach 25 kt by late this afternoon, particularly in the outer
zones. This uptick in winds is coinciding with a building
westerly swell, pushing combined seas toward 10 to 11 feet by
Saturday. As a result, Small Craft Advisories will be in effect
for all waters by this afternoon, with conditions likely
persisting through at least Saturday. By late Saturday night and
into Sunday, both winds and seasons will begin to ease as high
pressure weakens slightly and moves inland. The start of next
week looks to be rather quiet, with seas around 5 to 7 feet and
wind gusts under 20 kt.-Hall/JLiu

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...None.
WA...None.
PZ...Small Craft Advisory from 2 AM Saturday to 2 AM PDT Sunday for
     PZZ251>253.
     Small Craft Advisory until 2 AM PDT Sunday for PZZ271>273.

&&

$$

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