Funnel Cloud in Washington, August 23, 2024

Area Forecast Discussion
National Weather Service Portland OR
229 PM PDT Fri Aug 23 2024

.SYNOPSIS...An upper level low will maintain cool and showery
conditions through Saturday before the area starts to dry out as a
broad, shortwave ridge starts to build over the Pacific NW for the
majority of next week. There is also a 20%-25% probability of
thunderstorms across the forecast area through this evening. Offshore
flow develops late Wednesday/Thursday  and will result in warm and
dry conditions returning to the region.

&&

.DISCUSSION...Tonight through Thursday..Cool and moist conditions
will persist through Saturday as a broad area of low pressure slowly
moves eastward through the start of the weekend. This will result in
showers continuing through the evening hours along with a 20%-25%
probability for thunderstorms across the CWA through the evening.
Model soundings are showing CAPE values around 300-1000 J/kg and
while the upper end of those values are from the GFS (which tends to
be somewhat heavy handed), the fact that we have already observed
some lightning within our CWA as well as on the east side of the
Cascades and across NWS Medford's CWA, the overall thunder  forecast
and timing are continuing to look on track. We will continue to
monitor and adjust the very short term forecast as needed.

Saturday, cool and moist conditions will persist, but the
aforementioned low will be east of the Cascades and will result in
less frequent showers and will be the start of the somewhat slow
pattern shift which is expected through next week. Overall, the
pattern change will look something like this. Sunday into Monday, the
upper level pattern will become more zonal (west to east flow) as a
shortwave ridge builds in from the eastern Pacific which will contend
with an upper level low moving eastward across Canada. This will
maintain weak onshore flow at the surface, but daytime temperatures
will start to warm up into the 70s and 80s. This upper upper level
low will also drag a weak front across the northern part of our CWA,
which will likely bring very light rain to SW Washington and the very
northern parts of NW Oregon late Monday/early Tuesday.

By Tuesday the shortwave ridge will become the dominant synoptic
feature and as such the warming and drying trend will persist.
Wednesday and Thursday the shortwave ridge will build as it quickly
moves east of the Cascades and over the Great Basin. While it is
still very far into the future, multiple models like the GFS, NBM,
ECWMF and as well as their respective ensembles, are showing a
thermally induced surface trough developing to the west or over the
crest of the Cascades. This means that easterly winds are in the
forecast. Currently, models are showing the PDX to DLS gradient
around -2 to -3 mb. If these conditions manifest, that would likely
result in easterly gusts around 20-25 mph for Thursday with a 20%-30%
probability of 30 mph. Now, to put this into perspective, during
Labor Day of 2020 there were recorded gusts of 60-70 mph within the
Columbia River Gorge. So, this is looking to be far below those Labor
Day winds. Still, this forecast is well over 6 to 7 days in the
future and the forecast will change.

Overall, cool and moist conditions will continue through Saturday.
However, a pattern change is expected early next week, which will
bring warm and dry conditions through next week as well as east winds
into the region Thursday. /42

&&

.AVIATION...Low pressure system off the central Oregon Coast is
continuing to produce scattered to widespread showers across the
region as of 21z Fri, with a handful of lightning strikes being
observed over the Willamette Valley from KSLE to KEUG. Surface
observations show primarily VFR ceilings at area terminals,
with some intermittent dips to MVFR in heavier passing showers.
Expect this trend to hold through around 03-06z, though mountain
obscurations can be expected to persist through the period.
Thunderstorm activity will wane 02-03z with the loss of daytime
heating. In the meantime, aside from an amendment for VCTS at
KSLE based on observational trends, there is still not enough
confidence in thunder occurring at any given TAF site to warrant
mention of TS. Showers diminish in coverage by 06z Sat as the low
begins to split and most of the energy is shunted south of the
area. This will leave mainly VFR skies across the area, though hi-
res guidance does depict a 20-30 percent chance for MVFR cigs to
redevelop after 09z Sat.

PDX APPROACHES...Scattered showers will continue to intermittently
impact the terminal through 03-06z Sat, with around a 10-15
percent chance of thunderstorms in the vicinity through 02z. VFR
conditions prevailing through the remainder of the period, with
periods of MVFR cigs remaining possible in passing showers through
06z Sat. /CB

&&

.MARINE...Surface analysis places a low pressure center over the
coastal waters between Florence and Cape Blanco as of early Friday
afternoon, with buoy observations reporting 10 to 15 kt southerly
breezes and seas around 5 feet. Expect these general conditions to
persist through Saturday afternoon as low pressure slowly pushes
inland and a modest northwest swell maintains seas around 3-5 feet
at 8-10 seconds. Winds will trend light and variable on Sunday as
weak high pressure builds closer to shore. Stronger surface high
pressure will then build offshore early next week and yield a more
summerlike northerly wind regime as inland warming helps to
tighten the coastal pressure gradient. Guidance continues to
depict a 50-80 percent chance for Small Craft Advisory level wind
gusts across the waters by Tuesday, with the strongest winds
likely to be found south of Cape Foulweather. Seas will also be
trending upward early next week as building short period seas
combine with a building northwest swell to produce 7 to 9 ft seas
by Tuesday.

In the meantime, strong ebb cycles will continue to produce choppy
seas and make for potentially challenging bar crossings through
Saturday evening. However, background wave heights remain too low
to issue a Small Craft Advisory for the Columbia River Bar. /CB

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

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

&&

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Preliminary Local Storm Report
National Weather Service Portland OR
427 PM PDT Fri Aug 23 2024

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0415 PM     Hail             4 ENE Blue River        44.16N 122.25W
08/17/2024  E1.00 Inch       Lane               OR   Public

            Photo on social media from Rainbow, OR. Time
            estimated from radar.

&&

CN

Preliminary Local Storm Report
National Weather Service Portland OR
427 PM PDT Fri Aug 23 2024

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0358 PM     Hail             4 ENE Blue River        44.16N 122.25W
08/17/2024  E1.00 Inch       Lane               OR   Public

            Photo on social media from Rainbow, OR. Time
            estimated from radar.

&&

CN

Preliminary Local Storm Report
National Weather Service Portland OR
556 PM PDT Fri Aug 23 2024

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0512 PM     Funnel Cloud     1 SW Ellsworth          45.60N 122.58W
08/23/2024                   Clark              WA   Public

            A picture of a funnel cloud, taken by a
            member of the public was shared with us via
            social media from a local reporter. Looked
            at radar information around the estimated
            time of the photo and there was evidence of
            very weak rotation at the approximate time.

&&

DAB