Funnel Cloud in Washington, September 25, 2024

Area Forecast Discussion National Weather Service Portland OR 241 PM
PDT Wed Sep 25 2024

.SYNOPSIS...Cold front is moving through the rest of today and
tonight, which will bring widespread rainfall and breezy winds.
Thursday will bring a brief lull in active weather, aside from
lingering fog, Thursday afternoon. Another weaker front arrives
overnight into Friday late Thursday into Friday morning. High
pressure returns over the weekend. More active weather expected mid-
week.

&&

.SHORT TERM...Now through Saturday...The front has moved ashore, and
rain has begun throughout the CWA. The initial leading edge of the
front produced some thunderstorms in the Cascades that were slightly
stronger than previously forecast, with some fairly frequent
lightning production for about half an hour. However, these have
moved over the Cascades, and with daytime heating cut off,
instability is likely to fall apart over the rest of the afternoon.
While further thunderstorms in the Cascades can't be completely
ruled out, weakening instability is likely to make any further
thunderstorms very isolated. The front in general has also slowed in
its progression, and some slightly more substantial accumulations
are possible. The Willamette Valley will see between 0.25-0.5" of
total accumulation over the entirety of Wednesday, and closer to 1"
at the coast, Willapa Hills, and Coast Range.

Thursday sees more zonal flow, with any residual showers ending in
the morning. With clearing skies over Wednesday night, expect some
fog throughout the region near the end of Wed night and early Thu
morning. A very weak low moves through Thursday evening, but looks
to be aimed towards central Washington; only southwest WA should see
any accumulations. Friday and Saturday are very similar, with some
weak lows coming in at times that could produce a few hundredths of
an inch of accumulations at times. Cooler temperatures and higher
RHs expected during this period, with generally north/northwesterly
flow.
/JLiu

.LONG TERM...(Sunday through Tuesday)...
No significant changes. High pressure will remain over the region,
maintaining temperatures more typical of late September for Sunday.

Bit of change for early next week, as the high pressure shifts east
of the Cascades, and thermal low pressure develops along the coast.
This will bring a bit of offshore flow, not much in way of wind, but
enough to get warmer daytime temperatures, with inland highs back
into the mid to upper 70s for Monday and Tuesday, and upper 60s to
lower 70s along the coast. As is the case this time of the year,
offshore flow will also bring dry air, allow temperatures to drop
more quickly overnight. In areas where the east to northeast wind
drops off (such as valleys in the Coast Range and Cascade foothills,
as well as the Cowlitz Valley and Willamette Valley to south of
Portland, temperatures will be somewhat cool, with overnight lows in
the 40s. But, in areas with a bit of easterly wind, overnight lows
will stay in the 50s.

&&

.AVIATION...Predominantly VFR as of 21Z Wed as a front moves
ashore. Heavier showers ahead of the front now moving into the
interior valley and expect occasional MVFR conditions until the
front moves through. Also thunderstorm activity is fairly active
over the much of the Oregon Cascades. These storms should end or
be east of the Cascades by 00Z Thu.

Fog and low stratus on the coast has lifted but still a mix of IFR
to VFR with the precipitation. Showers taper off this evening,
with conditions expected to remain a mix of VFR and MVFR at the
coast overnight. Inland areas - there is a mix of VFR and MVFR
which is expected to continue through about 00Z-02Z Thu. Then for
the remainder of tonight expect mainly VFR conditions at inland
TAF sites. Early Thu morning, after 10Z or so, may see some MVFR
cigs back build from the Cascade foothill to valley terminals.

PDX APPROACHES...A mix of VFR and MVFR with rain chances with the
incoming front peak through 00Z Thu. Southerly winds expected to
increase to around 6-10 kt shifting to the west later this
afternoon, around 00z. VFR expected overnight, but there is about
a 30-50% chance for MVFR cigs to materialize after 10Z Thu.
/mh /DH

&&

.MARINE...Front moved ashore this afternoon and seas have
increased to 10 to 13 ft with a northwest swell. As westerly winds
ease behind the front expect seas to remain above 10 ft through
the evening hours, so have a Small Craft Advisory through this
evening.

Winds turn southerly again on Thursday ahead of another frontal
system. A developing low pressure will rapidly intensify across
the far NE Pacific and move toward Haida Gwaii, while pushing a
front toward the coastal waters later Thursday. The strongest
winds associated with this system are expected across the northern
waters. Model guidance shows probability of Gale Force southerly
wind gusts exceeding 33 kt to around 50% Thursday afternoon and
evening. The trailing cold front will likely weaken as it moves
across the coastal waters Thursday night.

A westerly swell moving in behind the front is expected to build
seas to around 12 to 14 ft on later Thursday into Friday. High
pressure also rebuilds on Friday, along with a strengthening
thermal trough along the southern Oregon coast. This will result
in a return to gusty northerly winds. Northerlies are likely to
continue through the weekend, while seas settle to around 8 to 10
ft. /mh /DH

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...None.
WA...None.
PZ...Small Craft Advisory until 10 PM PDT this evening for
PZZ251>253-
     271>273.

     Small Craft Advisory from 11 AM Thursday to 2 AM PDT Friday for
     PZZ251-271.
&&

www.weather.gov/portland

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