Tornado in Oregon, October 24, 2022

Area Forecast Discussion
National Weather Service Portland OR
401 PM PDT Mon Oct 24 2022

.SYNOPSIS...An active weather pattern continues to bring periods of
valley rain and high mountain snow for much of the week. A stronger
system Tuesday evening will bring some impactful snow amounts to the
Oregon Cascade passes and above. Therefore, a Winter Weather Advisory
has been issued for elevations 4000 feet and above Tuesday night.

&&

.SHORT TERM...Tonight through Thursday...A fall system pushed a front
over the forecast area today, and now a showery post-frontal regime
is left in its place. Satellite imagery shows the nice bubbly cumulus
moving down from the northwest, and radar shows some active showers
with moderate rainfall rates in their cores. With the instability
expected to remain through the afternoon and early evening, and the
post frontal shear, some of these cells may be able to produce some
small hail, and even a short lived funnel cloud. Current snow levels
are near 4500 over southwestern WA, and near 8000 over southeastern
Lane County. Colder air aloft will be pushing down those snow levels
this evening and overnight, at or around the Cascade passes. Showers
will be trending weaker and with less coverage through the night, and
some clearing in the clouds will allow minimum temperatures to lower
into the 30s and 40s, with a few high elevations being below
freezing.

A system west of Haida Gwaii will then drop down an curve into the
Pacific Northwest tomorrow, spreading it's frontal system in starting
in the late afternoon. While precipitable water values are not that
anomalous, the cold air advection and northwest flow will be
favorable for accumulating snow into the Cascades. This colder air
will push snow levels even further down near 3500-4000 by Tuesday
night. QPF amounts of near an inch expected in the mountains during
Tuesday night should result in 4 to 8 inches of snow at pass levels.
Therefore, have issued a Winter Weather Advisory to be in effect
then. Persons with travel plans over the passes should make sure
themselves and their vehicles are prepared.  Over the valleys and
elevations lower than 3500, expect rainfall amounts of 0.50-1.0
inches over Tuesday afternoon and into Wednesday morning. Another
impact from this system will be the energy that comes from the
instability induced by the system. HREF shows an area of 10-40
probability of thunder in a 4 hour period pushing onshore late
Tuesday afternoon, waning to 10-20 percent chance by midnight over
most of the forecast area. Forecast soundings show a good vertical
profile for the chance of thunder, so kept the previous forecast that
already had it in.

Northwesterly flow will keep cool temperatures and showers for the
area on Wednesday before a shortwave ridge will builds in Wednesday
night. This ridge will quickly be pushed south toward the Pacific
Northwest to bring a quick warmup on Thursday, before the front
pushes inland on Thursday night. /Kriederman

.LONG TERM...Thursday night through Saturday...GFS and EC differs on
whether or not to bring this frontal band inland from the Pacific.
Either way, this system has a stronger jet associated with it as well
as a good connection to an atmospheric river of moisture. Will
continue to monitor the agreement between models with this system as
it could bring a good swath of rainfall in with it, with warmer
temperatures, and snowlevels in the 8000-10000 ft range. The overall
pattern keeps a longwave trough over the western coast of North
American, so will likely continue to see the normal active fall
pattern to last. /Kriederman

&&

.AVIATION...18Z TAFs: Mainly MVFR this morning due to widespread
rainfall moving over the area. Along the coast, rain has begun to
let up, so should start to see some improvement over the next few
hours. Inland terminals will be slow to see CIGs lift as the
showers will likely remain. However, once skies become broken this
afternoon, the sunbreaks will likely assist in improving
conditions to VFR. Some visibility challenges persist due to
increased winds and continued rain but again, as the front pushes
eastward, will see steady improvement. Overnight, will likely see
the clouds fill back in with radiational cooling and could see
some marginal MVFR skies. Not seeing too much impact to visibility
throughout much of the area, but could see some reductions due to
patchy fog/mist, and any lingering showers.

Another cold front will move over the region late in the forecast
period, but could see the initial stages of rain, lowered
visibility, and degraded CIGs right along the frontal boundary.
These conditions, if they occur, would impact the coastal
terminals first.

KPDX AND APPROACHES...MVFR through the next several hours with
improvement expected around 22Z Monday. There is around a 30%
chance that MVFR CIGs could persist, but with rain coming to an
end, trending towards VFR. Winds will be light with a trend
towards the southwest later in the forecast period. The cold front
is not expected to impact the terminal in the next 24-hours.

-Muessle

&&

.MARINE...Buoy observations as of 3 PM show seas continuing to
hold around 10 ft at 8 seconds. Buoy 46005 is currently at 19 ft
at 16 seconds, these steep waves will disperse and move across
the coastal waters as a 14-15 ft wave group producing hazardous
sea conditions across the offshore waters, PZZ271/272, during the
overnight hours. Have upgraded the Small Craft Advisory to a
Hazardous Seas Warning through about 11 PM tonight. Seas will come
down into the low teens Tuesday morning. The Small Craft Advisory
across all waters then remains through Wednesday morning.

Active weather continues through the week as additional frontal
systems move across the waters. The WCwave10 and high resolution
NWPS guidance suggests seas of 15 to 18 ft Thursday night through
Friday.

The new moon on Tuesday will produce stronger tidal currents
during the evening ebb cycle. Those moving in and out of harbors
and crossing coastal bars should use caution and be aware of any
bar restrictions in place. -BMuhlestein

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...Winter Weather Advisory from 6 PM Tuesday to 6 AM PDT Wednesday
     for Cascades in Lane County-Northern Oregon Cascades.

WA...None.

PZ...Small Craft Advisory until 5 PM PDT Tuesday for Columbia River
     Bar.

     Small Craft Advisory until 11 AM PDT Wednesday for coastal
     waters from Cape Shoalwater WA to Florence OR out 10
     nm.Waters from Cape Foulweather to Florence OR from 10 to
     60 NM.

     Small Craft Advisory until 5 PM PDT this afternoon for coastal
     waters from Cape Shoalwater WA to Cape Foulweather OR from
     10 to 60 nm.

     Small Craft Advisory from 11 PM this evening to 11 AM PDT
     Wednesday for coastal waters from Cape Shoalwater WA to
     Cape Foulweather OR from 10 to 60 nm.

     Hazardous Seas Warning until 11 PM PDT this evening for coastal
     waters from Cape Shoalwater WA to Cape Foulweather OR from
     10 to 60 nm.
&&

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