Small Craft Advisory 193, NWS Portland, OR

Area Forecast Discussion...UPDATED
National Weather Service Portland OR
844 AM PST Wed Nov 17 2021

Updated short term forecast and aviation discussion

.SYNOPSIS...After a chilly start this morning, expect a dry day
with seasonal temperatures. Offshore winds will persist through
the day and will be quite gusty in the favored areas such as
the Gorge. Another system will likely bring light rain Thursday
and Friday before a dry and pleasant weekend. Another front
arrives early next week.

&&

.UPDATE...Made a few minor changes to the sky cover, fog, and hourly
temperature forecast for the rest of this morning. Patchy fog and low
stratus was lingering across the southern Willamette Valley, which is
now reflected well in the forecast. Expect areas of fog to lift by
9-10 AM PST this morning, with stratus breaking up by noon at the
latest. Observed temperatures at 830 AM were running quite a bit
cooler than forecast, with temperatures still in the upper 20s to
upper 30s across the area (coldest in locations such as Corvallis,
Battle Ground, Kelso, and Tillamook). Temperatures should rise
quickly late this morning into the early afternoon, topping out in
the upper 40s to lower 50s for the lowlands. High clouds will also
push into the region this afternoon ahead of the next weather system,
but skies should remain partly to mostly for the rest of this
morning. -TK

&&

.SHORT TERM...THROUGH FRIDAY NIGHT...Upper level ridging is
producing mostly clear skies over the Pacific Northwest early
this morning, with temperatures dipping well into the 30s
across northwest OR and southwest WA as a result. The
combination of clearing and antecedent low level moisture from
recent rainfall has also lead to some patchy fog development
through the Willamette Valley and along the 1-5 corridor in
southern WA. Meanwhile, an inverted surface trough located
along the northern CA/southern OR coast is beginning to shift
northward along the coast and strengthen the offshore pressure
gradient, which will yield increasing easterly winds today along
the Cascade Crest and foothills and through the Columbia River
Gorge. These easterly winds should also help to scour out any
fog relatively quickly this morning, setting the stage for a
pleasant dry day with temperatures in the low 50s across the
area. High clouds will be on the increase this afternoon and
evening as the ridge axis slides east of the Cascades and gives
way to southwest flow aloft ahead of the next shortwave trough
approaching the area late in the week. Warm frontal
precipitation associated with this system will spread into the
area either very late tonight or more likely Thursday morning
and persist through Thursday night. Rainfall totals still look
rather tame for this system, with generally a quarter to a half
inch expected in the valley and up to 1 inch with locally higher
amounts in the Coast Range and the Cascades. Hydro concerns
therefore remain minimal through the end of the week. Some of
the Cascade passes could see some light snowfall at the onset of
precipitation on Thursday, but snow levels will quickly rise
above 5000 feet in the warm advection regime, keeping winter
weather concerns at a minimum as well. Friday will see a
transition to more showery weather as the shortwave crosses the
region, with shower activity generally coming to an end from
west to east by Friday evening. /CB

&&

.LONG TERM...SATURDAY THROUGH TUESDAY...The extended part of
the forecast looks to begin with a stretch of pleasant late
fall weather this weekend as the return of upper level ridging
supports dry and mostly sunny conditions with afternoon highs
remaining near seasonal normals in the low 50s. This is well
supported by WPC cluster analysis, with ensemble members in
strong agreement on the general pattern despite some differences
in the strength and placement of the ridge. Some chilly and
potentially frosty mornings will also be possible given the
potential for clear skies and light winds with high pressure
overhead. The next system then approaches the region sometime
early next week in the form of another Pacific shortwave.
Details are still to be worked out as models differ on timing of
this system impacting the region from as early as Sunday night
to as late as Tuesday. Still, the bulk of ensemble members
produce at least some rain at PDX early next week, sufficient to
carry relatively broad-brushed likely PoPs next Monday-Monday
night. This system does not look to be overly impactful in
terms of rain amounts are wind at this time, but will obviously
continue to monitor in the coming days. /CB

&&

.AVIATION...18z TAFs: As of 1630z, VFR conditions prevailed
through most of the forecast area. Main exception is in the
Willamette Valley south of KSLE, where fog and low stratus
persist. The fog/low cloud layer remains shallow, so expect
lingering clouds to mostly dissipate by 18z or 19z. VFR will
prevail thereafter.

Otherwise, offshore flow is keeping most areas clear of low
clouds. The E-NE winds are rather breezy in some areas,
especially along the coast and near the west end of the Columbia
Gorge. East wind gusts 15-25 kt are likely through the Oregon
Coast Range gaps through about 00Z Thu. Gusts 25-35 kt can be
expected in the south Washington and north Oregon Cascade
foothills, with peak gusts 35-45 kt at the west end of the
Columbia River Gorge. The east wind will become confined closer
to the Gorge Wed evening.

For detailed  regional Pac NW aviation weather information, go
online to: https://weather.gov/zse

KPDX AND APPROACHES...VFR expected through 12Z Thu. Northeast to
East wind strengthens during the morning, with gusts 25-35 kt
east of KPDX through Wed evening.  Weishaar/Weagle

&&

.MARINE...Thermally-induced surface low pressure along the coast
early this morning will continue to strengthen and expand north
through the morning. This will result in gusty northeast to east
wind, especially in the coastal terrain gaps and over portions of
the PZZ270 that are directly aligned with said gaps. Will
continue with the current small craft advisories.

The offshore pattern weakens this afternoon and tonight as the
wind becomes southeast to south ahead of the next frontal system.
The 06Z NAM, 00Z GFS and 00Z ECMWF are in general agreement
showing a rapidly developing surface low pres area moving to near
43N 131W by 18Z Thu. Small craft advisory speeds are likely to
develop over PZZ255 and PZZ275 early Thu morning. The wind
forecast becomes more muddled Thu afternoon through Thu night.
The aforementioned operational models show differing paths with
the surface low. The general idea is for the bulk of the energy
to be focused over the south Oregon and north California waters.
There is a possibility of gale force gusts for PZZ255 and PZZ275
late Thu afternoon through Thu evening. Not confident enough at
this time to go with a Gale Watch. The surface low eventually
weakens and moves ashore somewhere near KTMK per the NAM
solution, or KONP per the ECMWF solution, or near KOTH per the
GFS answer. The wind eventually shifts to north Fri, with 20-25
kt gusts likely Fri afternoon. High pressure settles over the
waters during the weekend with wind speeds generally 15 kt or
less.

Wave heights continue be a foot or two higher than model
guidance. At 0930Z buoy 46248 was at 8 ft, slightly higher than
the model forecast. Seas will continue to diminish as the
offshore pattern develops. Seas may reach 10 ft Thu evening over
the far southern part of the forecast area where gale force gusts
are possible. Seas may also get close to 10 ft Fri afternoon and
evening with the northwest to north wind pattern. Weishaar

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory until 4 PM PST this afternoon for Waters
     from Cape Shoalwater WA to Cascade Head OR from 10 to 60
     nm.

     Small Craft Advisory until 10 AM PST this morning for Waters
     from Cascade Head to Florence OR from 10 to 60 nm.

&&

www.weather.gov/portland

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