-- Discussion containing changed information from previous version are highlighted. --
766
FXUS66 KPQR 251804 AAA
AFDPQR

Area Forecast Discussion...UPDATED
National Weather Service Portland OR
1104 AM PDT Sat May 25 2024

Updated aviation discussion.

.SYNOPSIS...
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Cool and cloudy again today with lingering showers
into the afternoon. Trending warmer and drier on Sunday with the
exception of some light rain chances continuing across the far
north. Temperatures will peak on Monday, then trending back down
through the middle of next week as the next system brings
additional rain chances.
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&&

.SHORT TERM...
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Now through Monday Night...The upper level
pattern features troughing which extends from the BC Coast to
just east of the Oregon Cascades, with scattered showers
continuing across northwest Oregon and southwest Washington in
deep layer northwest flow. This will result in another
seasonably cool and cloudy day across the area as scattered
showers continue into the afternoon and high temperatures only
reach the low 60s across the interior lowlands. Rainfall amounts
will generally be minimal today as the trough shifts east of
the region, with most locations remaining below a tenth of an
inch aside from some locally higher amounts approaching a
quarter inch on favored Cascade slopes. Showers will mostly
taper off by this evening as transient shortwave riding crosses
overhead. Skies are beginning to clear this morning which, if it
persists, could set the stage for some radiational cooling in
valleys. At this point, models are suggesting only a 20-30%
chance for fog or at least lower stratus from Salem southward in
the Willamette Valley. But, with the inversion possible near the
surface, valleys of the Coast Range and Cascade Foothills could
see some patchy misty fog that could temporarily impact
visibility. Will continue to monitor over the next few hours.

Sunday will be characterized by benign zonal flow aloft,
yielding partly cloudy skies and temperatures rebounding to
around 70 in the interior valleys. Expect dry conditions across
most of the area, though a few raindrops can`t be ruled out
across southwest Washington and the far northern Oregon Coast as
a weak disturbance crosses the Washington Coast. The warming
trend continues into Monday with sunnier skies across the area as
a ridge builds east of the Cascades, pushing temperatures well
into the 70s in most locations away from the coast.
Probabilistic guidance continues to indicate a 30 percent
chance for highs to reach 80 degrees in and around the Portland
Metro. A chance for rain returns to coastal areas as early as
Monday night as the next system begins to approach from the
Pacific. -Muessle/CB

.LONG TERM...Tuesday through Friday...Temperatures begin to
trend back down on Tuesday as the ridge axis shifts farther east
towards the Rockies, increasing the influence of the next upper
level trough encroaching upon the Pacific Northwest from the
Gulf of Alaska. WPC ensemble clusters remain in reasonable
agreement (~70 percent of members) on keeping a troughy pattern
over the region through Thursday, resulting in cool and showery
conditions with temperatures generally in the 60s through most
of next week. Guidance diverges beyond Thursday, which is
reflected by a 20 degree spread between the 25th and 75th
percentile for NBM high temperatures by the end of next week.
-CB
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&&

.AVIATION...
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Showery conditions persist from KSLE northward with
heaviest rain along the coast. With passing showers expect periods
of gusty winds and possibly reduced visibility. Some IFR CIGs
have been reported around KAST this morning with the passing
showers. Otherwise, VFR CIGs and VIS expected over the next 24
hours. With sun breaks beginning to peek through the overcast
skies, it will allow for more radiational cooling at night and
thus, increased chances for fog. High resolution models and
forecast soundings are showing around a 20-30% chance of fog with
at least MVFR CIGs in the lowlands from KUAO southward including
KCVO and KEUG. However, confidence is low so have only included
the mention of it in the TAF. Will have to continue to watch these
conditions as yet another weak disturbances passes through the
atmosphere after 10Z Sunday. This disturbance will increase
mixing, and could bring another round of non-impactful rain.
Winds will be west-northwest through the forecast.

PDX AND APPROACHES...VFR for the next 24 hours with some lingering
showers through 00Z Sunday. Reduced VIS/CIGs possible in passing
showers but will be short-lived. Otherwise, no weather concerns.
-Muessle
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&&

.MARINE...
As the system continues east out of the region, winds
and seas will gradually ease into Saturday morning. Will maintain
the current timing of the Small Craft Advisory, set to expire 11AM
Saturday. Another weak ridge of high pressure brings the return
of benign conditions by Saturday afternoon and these lower
conditions are expected to persist through the start of the
upcoming week. Monday night another system originating from the
Gulf of Alaska will start to move southward and arrive around
Tuesday/Wednesday. An increase of winds and seas across all
waters is expected. -JH

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory until 11 AM PDT this morning for PZZ210-
     251>253-271>273.
&&

$$

www.weather.gov/portland

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