126
FXUS66 KPQR 151639
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
340 AM PDT Thu Aug 15 2024

.SYNOPSIS...Cool and cloudy across the area again today, with
scattered showers and a slight chance of thunderstorms along the
Cascades through early this evening. Widespread wetting rain appears
likely across the area on Saturday as an unseasonably strong system
impacts the area, with showers lingering into Sunday. Seasonably
cool and cloudy weather then continues into the middle of next week.

&&

.SHORT TERM...Now through Saturday Night...Regional radar as of
early Thursday morning shows widespread showers across south-
central Oregon, with some of this activity clipping parts of
the Oregon Cascades as an upper level trough lifts northeastward
accompanied by an influx of mid level moisture. This activity
managed to produce a handful of lightning strikes along the
crest in far eastern Lane County earlier in the night, but
showers have mostly dissipated or remained just east of the area
as they encounter a more stable, less favorable convective
environment on the west side of the Cascades. Will continue to
see some spotty shower activity spread north along the Cascades
Crest today as the upper low continues to lift northeast across
the state, with a 15-20 percent chance of thunderstorms hanging
on along the Lane and Linn County Cascades through early this
evening.

Otherwise, locations west of the Cascades will see seasonably
cool and cloudy conditions in onshore flow today. Partial
clearing may allow for a few breaks of sunshine this afternoon
in the Willamette Valley, but expect clouds to linger through
much or all of the day in most locations, with highs generally
in the mid to upper 70s. Expect little change for Friday as
stable onshore flow maintains the status quo with another day of
temperatures in 70s.

A bigger change will arrive by Saturday as an unseasonably deep
upper trough digs southward along the West Coast and brings
wetter conditions across the area. Models depict a large closed
low residing off the Oregon Coast by Saturday morning, with a
piece of shortwave energy then swinging around the base of the
trough and across western Oregon from the south during the day
on Saturday. The combination of strong forcing and precipitable
water values around 1.25 inches exceeding the 90th percentile of
mid August climatology will produce widespread rain across the
area from early Saturday morning continuing into Saturday
night. Current probabilistic guidance gives most locations
around a 50-60 chance to see a wetting rain of at least a
quarter inch through Saturday evening, with the higher end
solutions suggesting as much as 0.75-1.00" of rain in some
locations by Saturday night. Most of the area will also see a
15-25 percent chance of thunderstorms during the day on
Saturday, although these would obviously be expected to be
accompanied by plenty of rain given the circumstances. /CB

.LONG TERM...Sunday through Wednesday...Rain will be starting to
taper off by Sunday morning as most of the energy associated
with the upper trough shifts north of the region, but certainly
could see a few showers linger into the day on Sunday and bring
minimal additional rainfall amounts to the area. The Pacific
Northwest will remain under the influence of broad upper level
troughing centered offshore through the middle of next week,
which is generally well agreed upon by ensemble guidance. As
such, expect a continuation of seasonably cool and cloudy
weather through the end of the period with daily highs remaining
in the mid to upper 70s. The proximity to the upper level
trough will yield continued chances for sporadic shower
activity, but no significant rainfall or thunderstorm potential
is signaled beyond Sunday morning. /CB

&&

.AVIATION....AVIATION...An upper level trough continues to push
through the region early this morning, maintaining onshore
flow. Currently as of 10Z Thursday, VFR conditions inland and
MVFR conditions along the coast. There is a 20-40% that CIGs
along the coast will lower to IFR between 10-17Z Thursday. The
one exception is KONP, with a 60-80% chance of IFR and 20-40%
chance of LIFR between 10-16Z Thursday. Expect inland locations
to remain VFR through the TAF period, with a 10-30% of MVFR CIGs
between 12-18Z Thursday. Otherwise, expect southwesterly winds
in the southern Willamette Valley, with wind direction shifting
northwesterly as you move further north.

PDX AND APPROACHES...Predominately VFR thresholds through the TAF
period, with a 10-30% chance of MVFR cigs between 12-18Z
Thursday. Northwest winds will remain well under 10 kt.
/Sala

&&

.MARINE...Expect benign conditions over the waters through early
next week. Winds remain N/NW through Saturday before turning SW
as surface low pressure develops. Winds are expected to remain at
10 kts or less with gusts up to 15 kts; wind-driven seas of 2 of
4 feet. -Batz

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...None.

&&

$$

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