Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 282250

Area Forecast Discussion
National Weather Service Portland OR
250 PM PST Sun Feb 28 2021

Updated Short-term and Aviation sections

.SYNOPSIS...Largely dry and mild weather for the next several
days as valley temperatures moderate into the 50s and quite possibly
climb into the 60s by Thursday. Coastal drizzle with spotty light
rain across the far north will be possible through late Monday.
Otherwise, dry weather dominates the pattern through most of
Thursday. Then, a more substantial storm system will likely bring
moderate rain and mountain snow totals Thursday night and Friday
followed by unsettled conditions through the weekend.


.SHORT TERM...Tonight through Wednesday...Very pleasant afternoon as
clouds have cleared out for much of the region. Ended up increasing
this afternoon`s temperatures a little across the north as the fair
weather cumulus from earlier today has pushed north. Areas west and
north of Portland proper are still under fairly overcast skies.
Clouds will increase again tonight as the minimal remnants of an
approaching front will push moister marine air inland. May get some
patchy fog ahead of the incoming clouds, especially for the central
and south valley.

Have mostly removed PoPs from the forecast area to now leave Monday
and Monday night dry for the bulk of the CWA. The energy diving
south along the offshore trough is now pinching off into a closed
low west of 130W with only a small reflection of the original trough
represented in the northern branch of the split. However, that small
remnant shortwave will clip the area. Will leave very low rain
chances Monday afternoon for the far northern coastal areas and then
spreading inland, mainly north of the Columbia, Monday evening. Any
amounts would be minimal. The persistent onshore flow will bring
some lift through the lower clouds and have added drizzle to the
entire coast from Monday through much of Tuesday.

Another trough starts digging south along 145W from the Gulf of
Alaska Tuesday night. It will stay well offshore while the
aforementioned cut off low, now off the SoCal coast will aid in
bringing warmer air north to the region. This will help bring
temperatures toward the upper 50s by Wednesday afternoon. /JBonk

.LONG TERM...Wednesday night through Sunday...No overly significant
changes to the long-term as large scale model agreement remains good
beginning Wednesday night in further deepening the offshore trough
while ejecting the cut-off low inland across the desert southwest.
The pattern amplifies further Thursday with ridging pushing north
along the Rockies. Am now fairly confident Thursday I-5 corridor
temperatures will reach into the 60s from Eugene north through SW

Subtle details in the frontal progression differ from Thursday night
through Friday night. Regardless of the model solution, there
appears to be a common thread of a 12-18 hour period where some
portion of the larger PacNW area can get 1-2 inches of rain. 12Z
operational models are now pushing that area toward SW Oregon.
Unstable conditions will trail through the weekend with plenty of
shower activity seeming likely. /JBonk


.AVIATION...High pressure remains over the area with little
change expected in the overall forecast. Expect widespread VFR
cigs with some cumulus around 4000-5000 ft. Throughout the day
today, satellite has shown much less cloud cover than previously
expected so there has been more daytime warming. If skies remain
clear or almost clear through the early evening, could see a bit
of patchy fog throughout the area as radiational cooling takes
place. Models are suggesting a dewpoint depression around 3
degrees which is borderline fog/low patchy stratus and conditions
being too dry for formation. Coastal areas are a bit more
questionable in regards to fog as it is possible that the coast
may just see the VFR skies lower to upper level MVFR instead of
developing fog. Ultimately, low confidence in the conditions
expected after 11Z Mon. By 17Z Mon though, any developed fog or
MVFR cigs will lift and a return to sunny skies. Winds will be
variable through the early evening but should become southerly by
06Z Mon although speeds will remain below 10 kt.

For detailed regional Pac NW aviation weather information, go
online to:

KPDX AND APPROACHES...No impacts expected. Possibility for some
patchy ground fog between 10Z-16Z Mon but confidence is low.
Otherwise, VFR conditions with southerly winds through the
overnight hours.  -Muessle


.MARINE...A ridge of high pressure over the central Oregon coast
waters lingers through the middle of the week. A weakening and
decaying front will approach the area on Monday which could bring
a brief period of increased northwest winds, especially in the
northern waters west of 30NM. Expecting winds 10-15 kt with gusts
up to 20 kt but could see gusts up to 25 kt in the far northern
portions of PZ270. During that time, seas will remain around 6-8
ft at 13 seconds through at least Monday afternoon as seas begin
to slowly build to 10-12 ft at 13 seconds by Tuesday afternoon.
Seas will ease overnight Tuesday and remain benign through
Thursday morning.

The next system will occur in the late Thursday/early Friday
time frame. This front appears to be more robust than the
systems earlier in the week. Some global models are suggesting
near gale force gusts near 40 kt while others are staying more in
the 25 to 30 kt range. Expecting solid small craft level winds
and not biting on the gales at this time. Will say though, if the
pressure gradient continues to intensify, could see a slight
coastal jet develop. Similarly, seas will be impacted by a
secondary fresh swell that happens to be the more energetic of
the two. Recent models have begun to lower both the primary and
secondary swells associated with this system; although wind
waves remain elevated. Combined seas are trending lower to 15-18
ft which is very common to see occur as an event nears. -Muessle


PZ...Small Craft Advisory until 9 PM PST this evening for Columbia
     River Bar.

     Small Craft Advisory from 3 AM to 8 AM PST Monday for Columbia
     River Bar.



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