Flooding in Oregon, January 28 to 31, 2024

Area Forecast Discussion
National Weather Service Portland OR
339 AM PST Sun Jan 28 2024

.SYNOPSIS...Moderate to locally heavy tapers off this morning as the
region heads to a brief dry period later today into Monday.
Drier weather unseasonably warm temperatures this afternoon
into Monday. More unsettled weather returns by Tuesday and
continues through much of the week, with cooler temperatures
expected towards the end of the week.

&&

.SHORT TERM...THROUGH MONDAY NIGHT...Radar and satellite showing back
edge of rain moving onshore as a wave lifts north into western WA.
Rain amounts in the past 12 hours ending at 2 am were about 0.75 to 1
inch at the coast/coast range, south WA Cascades; and 0.1 to 0.3
inches in the interior lowlands.  Rain rates will taper off through
the morning with mainly dry weather later in the afternoon into
Monday. The next system presently between 130 and 140W off the west
coast will track north with the trailing front remaining offshore
through Monday.  Deterministic and ensembles are in good agreement
with a dry period later today into Monday afternoon. Rain then
returns Monday night into early Tuesday as the weakening frontal
system shifts inland.

In addition to the dry weather will see unseasonably warm
temperatures next several days with temperatures near record high
today.	Currently temperatures in the mid to upper 50s across lower
elevations. Though colder air east of the Cascades is filtering
through the Gorge holding temperatures in the 30s at Hood River to
mid 40s along the Columbia River in the Portland area. East winds
ease this morning then increase again by tonight so will likely
continue with the trend of cooler temperatures right along the
Columbia River into Monday.

.LONG TERM...TUESDAY THROUGH SATURDAY...An active and wet
pattern looks to continue from Tuesday through much of next
week as a strong jet keeps a series of systems focused on the
U.S. West Coast and brings periods of rain through much of the
long term. However, ensembles still show good agreement on
gradually shifting the storm track south towards California,
keeping the most impactful weather south of our region. There is
good agreement among WPC ensemble clusters that upper level
troughing pushes into the western US Thursday and Friday,
bringing a cooling trend with snow levels gradually falling to
more normal levels. This will at least bring snow potential
back below the Cascade passes by late in the week, but as of
now there is less than a 10% chance for lowland winter weather
by next Friday.
-CB/DH

&&

.HYDROLOGY...Warm temperatures and high dewpoints are leading to
efficient snowmelt today and will continue to do so for the next
several days. The snowmelt, along with periods of moderate rain, is
leading to high water on many area drainages.

Currently have Flood Warnings for 4 river points: Pudding at Aurora,
Luckiamute at Suver, Tualatin at Farmington, and Grays near Rosburg.
All except for the Grays are tracking well and expected to be
flooding this morning.	The Grays near Rosburg is presently below
flood stage and was trending down for most of the night, but now it
on an uptick. So will keep an eye on it for the next several hours to
see if trends change.

Aside from these points, we will need to watch all rivers draining
areas of snowmelt, especially in the Coast Range where model
analyses struggle with snowpack due to lack of SNOTEL coverage and
thick forest canopy making it difficult to properly assess the snow
situation below it remotely. Rainfall rates should remain modest
enough to prevent significant urban/small stream flooding, so the
issue this time around will primarily be with the larger mainstem
rivers. Weagle

Forecasts for these rivers can be found at www.nwrfc.noaa.gov or via
our website weather.gov/portland.

&&

.AVIATION...An area of light rain associated with a weakening
low was shifting northeastward over northwest OR and western WA as
of 11z Sunday with breezy south winds occurring at most TAF
sites, except at KTTD and KPDX where easterly winds continued
flowing out of the Columbia River Gorge. Cigs were LIFR to IFR at
the coast and are expected to linger through at least 18z Sunday
before cigs trend towards VFR around 21-22z Sunday. Inland TAF
sites were observing high-end MVFR to low-end VFR cigs, and this
trend should continue through Sunday morning before conditions
lift to VFR in the afternoon. Skies should attempt clearing out
altogether between 00-06z Monday while winds turn calm (except at
KPDX and KTTD where east winds will continue). This will set the
stage for some patchy fog development Sunday night, mainly over
the central and southern Willamette Valley. While fog will be
possible at KSLE, KEUG, and KHIO, fog is not expected at the coast
or in the northern Willamette Valley due to breezy offshore flow.

Note: METARs will not be available at KEUG from roughly 08Z to
14Z. Therefore, TAFs for this terminal may not accurately reflect
current observations.

PDX AND APPROACHES...Expect high-end MVFR to low-end VFR cigs with
periods of light rain through 16-17z Sunday before rain comes to
an end and cigs lift to VFR by the early afternoon.  -TK

&&

.MARINE...A weakening low was shifting north of the coastal waters
early Sunday morning. This has resulted in improving conditions,
as observations at buoy 050 showed south winds between 15-25 kt
with seas around 11 ft at 15 seconds. Expect very little change to
winds and seas through Sunday night. However, a frontal system
will bring increasing winds and seas late Monday into Monday
night, potentially strong enough to produce marginal gale force
wind gusts to around 35 kt. This is especially true over the outer
waters where the probability of gale force wind gusts is 70-80%.
However, probabilities quickly drop to around 40% over the inner
waters. Given how marginal conditions are, have decided to hold
off on a Gale Watch for now. However, will maintain a small craft
advisory for all marine zones through Monday afternoon.

After Monday, the next big weather maker of note arrives mid-week
when winds and seas will drastically increase. Although
uncertainty still exists with this system, chances for seas at or
slightly over 20 ft have increased a bit Tuesday night into
Wednesday, mainly over 30 nm offshore. It appears there will be a
tight gradient from the inner waters to the outer waters, as
south winds are expected to be much stronger over the outer waters
(at least gale force strength with a 20% chance for storm force
winds). Conditions do not look favorable for a low-level jet near
the coast given a slight offshore component to the surface winds.
-TK

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...None.
WA...None.
PZ...Small Craft Advisory until 10 AM PST Monday for Columbia River
     Bar.

     Small Craft Advisory until 4 PM PST Monday for Coastal waters
     from Cape Shoalwater WA to Florence OR out 60 NM.

&&

www.weather.gov/portland

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