Ice Storm in Oregon, January 21 to 22, 2024

Area Forecast Discussion
National Weather Service Portland OR
203 PM PST Sun Jan 21 2024

.SYNOPSIS...Rain showers continue across NW Oregon and SW
Washington with another round of widespread precipitation moving
through the region Sunday night into Monday. Temperatures in the
Columbia River Gorge have risen above freezing, with
precipitation transitioning to rain, while temperatures remain
at or below freezing in the Hood River Valley with a mix of rain
and freezing rain through Monday. Additional ice accumulations
are expected on top of the already substantial snow and ice
accumulations in the Hood River Valley. Elsewhere, southerly
flow aloft is gradually moderating temperatures, so freezing
rain is over and a slow thaw has begun across the Portland metro
and elsewhere in the Willamette Valley. Additional disturbances
and warm fronts will slowly chip away at the subfreezing air,
with freezing rain likely limited to the upper Hood River Valley
by Monday. Otherwise, surges of warm, moist air will continue
to bring rain through the upcoming week as snow levels remain
near or above the passes and temperatures gradually moderate to
near or slightly above normal. Snowmelt and additional rainfall
is leading to high water on some area rivers, but no rivers are
presently forecast to flood.

&&

.DISCUSSION...Today through next Saturday...Radar imagery early
Sunday afternoon shows rain showers continuing across NW Oregon
and SW Washington behind a weak frontal passage. Here's a brief
synopsis of the weather systems expected to move through the
region this week. Another round of widespread precipitation
will push from south to north through the region late Sunday
afternoon into early Monday morning as another compact frontal
system moves north along the coast. Showers will continue
through the day Monday into Tuesday morning as another weak
disturbance moves over the region. Tuesday afternoon and evening
will turn mainly dry as weak riding builds, with light showers
continuing in the higher terrain. Ensembles indicate another
couple of weather systems will push through the region Wednesday
into Thursday with a potentially wetter system Friday into
Saturday.

Now, to go into more detail. Temperatures continue to moderate
across NW Oregon and SW Washington today, slower in the Portland
metro area, Columbia River Gorge, and Hood River Valley.
Elsewhere will see high temperatures around or slightly above
normal for late January through the week. The main region of
concern today through this week is the Gorge, Hood River Valley,
and surrounding Cascades, mainly in SW Skamania County.
Temperatures as of 1 PM Sunday in the western Gorge have risen
around 3-4 degrees above freezing, which has eliminated the
freezing rain threat in this region. In the Hood River Valley,
temperatures have been rising very slowly throughout the day,
and are currently hovering around 30-33 degrees. This remains on
track with our hourly forecast temperatures. If this trend
continues, most locations in the Hood River Valley should reach
32-34 degrees by around 3-4 PM with a few pockets remaining
below freezing. Temperatures are expected to cool a few degrees
overnight, hovering right around 29-33 degree. 13Z NBM guidance
indicates a 30-50% chance temperatures will remain below
freezing through midday Monday whereas the 12Z HREF indicates
only a 10-20% temperatures will remain below freezing after 2 PM
Sunday and will remain above freezing after. This makes for a
complicated precipitation forecast in the Hood River Valley this
afternoon into Monday. Freezing rain with a mixture of sleet and
snow flakes will continue for locations that remain or fall
back to below freezing into Monday. Even if temperatures do
climb slightly above freezing and remain there, surfaces will
remain potentially icy and slick as any thaw will be very slow,
likely taking days. Still, temperatures climbing above freezing
should considerably improve conditions at river level, perhaps
leaving I-84 and WA-14 with just wet roads through the
west/central Columbia Gorge by Monday.

Our current forecast hedges more toward the NBM temperature
probabilities with temperatures hovering around freezing into
Monday morning, especially as the weather system Sunday night
will increase easterly winds through the Gorge which will lock
the low-level cold air in place in the Gorge. The temperature of
the low-level cold air once this happens will be crucial to how
much freezing rain accumulates into Monday and also with the
weather systems throughout the week. If temperatures do not rise
above freezing Sunday afternoon, temperatures will likely remain
this way through the week, which could bring significantly more
icing with each additional weather system. However, as mentioned
before, there's only a 30% or so chance this scenario will
happen. The more probable solution is temperatures at most
locations rise to just above freezing before the weather system
moves in Sunday night, which would allow for pockets of freezing
rain at times, mainly overnight when temperatures would be
likely to fall below freezing, and a mix of rain and freezing
rain at other times.

As it is, additional ice accumulations will continue to produce
significant impacts to trees, powerlines, and infrastructure as
the combination with past ice and snow will add to the weight
load, including on roofs. If the worst case scenario
materializes, it could lead to major damage as inches of ice
build up on area trees and power lines, and would exacerbate
weight loading issues for roofs of buildings in the area,
stressing some to the point of failure. Rainfall rates through
Monday could be high enough that at least some of the rain could
run off branches and power lines before getting a chance to
freeze, which is a mitigating factor for infrastructure issues
such as power outages.

The low moving up the coast Sunday night into Monday morning
will also produce a small area of breezy southerly winds. Along
the coast, expect gusts up to 35-45 mph, locally up to 50 mph
in wind prone beaches and headlands. NBM/HREF both show less
than a 10% chance of gusts over 55 mph. Additionally, east gusts
through the western Gorge will increase to 30-45 mph, locally
up to 55 mph for wind prone areas.

Will need to watch rivers over the coming days as the increasing
subtropical influence will keep snow levels higher than usual and
allow for the potential of heavier rain as the additional
frontal systems move through the region through the end of the
week. No rivers are forecast to enter flood stage at this time,
but a few flood prone rivers are forecast to peak in Action
stage. A look at the latest WPC cluster analyses suggests a
greater than 80% chance of upper level ridging developing next
weekend, which should finally give the region a break from the
active weather next week. -Weagle/HEC

&&

.AVIATION...Radar imagery and terminal observations as of 22z Sun
show rain showers across the region with a mix of IFR/MVFR cigs.
Later this evening after 00-03z Mon, another low pressure system
will approach the area and bring more widespread rain and with
predominately low-end MVFR/IFR cigs tonight. Winds will also turn
more southerly with this system. An exception would be the eastern
Portland Metro Area, where E/SE winds continue through the
Columbia River Gorge with gusts up to 20-25 kt near KPDX and 25-30
kt near KTTD. Southerly winds along the coast tonight could also
gust up to 20-25 kt. We'll maintain IFR/MVFR cigs throughout the
day Monday across all terminals with a showery pattern. Heavier
showers could bring brief reductions to visibility.

Note: Wind observations are down at KAST, and METARs will not be
available at KEUG from roughly 06z Mon to 14z Mon. Therefore,
TAFs for these terminals may not accurately reflect current
observations. Current NOTAM is EUG01/243.

PDX AND APPROACHES...Low-end VFR/high-end MVFR thresholds through
the rest of the afternoon. The next system arrives this evening,
so expect cigs to lower to predominately MVFR after 02-04z Mon.
Easterly winds continue throughout the TAF period, weakening after
15-18z Mon. -Alviz

&&

.MARINE... Tonight into Monday morning, a fast-moving low pressure
system will push through the waters from the southwest and strengthen
south/southwest winds with gusts up to 30-35 kt. Most of the Gales
are confined to the central and southern waters, so a Gale Warning
has been issued for those waters beginning this evening and lasting
through early Monday morning. Gales don't quite reach the northern
waters, so a Small Craft Advisory continues for that area. Seas
are forecast to climb up to 10-12 ft (highest near the southern
waters) and peak early Monday morning. Winds gradually weaken and
seas fall to 7-9 ft through the rest of the day Monday into Tuesday.
The next system looks to arrive Wednesday, which will return
gusty south winds and build seas.      -Alviz

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...Ice Storm Warning until 4 PM PST this afternoon for Central
     Columbia River Gorge-Upper Hood River Valley-Western
     Columbia River Gorge.

WA...Ice Storm Warning until 4 PM PST this afternoon for Central
     Columbia River Gorge-Western Columbia River Gorge.

     Winter Storm Warning until 4 PM PST this afternoon for South
     Washington Cascades.

PZ...Small Craft Advisory until 10 AM PST Monday for Coastal waters
     from Cape Shoalwater WA to Cape Falcon OR out 10 NM-
     Columbia River Bar-Waters from Cape Shoalwater WA to Cape
     Falcon OR from 10 to 60 NM.

     Small Craft Advisory until 7 PM PST this evening for Coastal
     waters from Cape Foulweather OR to Florence OR out 10
     NM.Coastal waters from Cape Foulweather OR to Florence OR
     from 10 to 60 NM.

     Small Craft Advisory from 4 AM to 10 AM PST Monday for Coastal
     waters from Cape Foulweather OR to Florence OR out 10
     NM.Coastal waters from Cape Foulweather OR to Florence OR
     from 10 to 60 NM.

     Gale Warning from 7 PM this evening to 4 AM PST Monday for
     Coastal waters from Cape Foulweather OR to Florence OR out
     10 NM.Coastal waters from Cape Foulweather OR to Florence
     OR from 10 to 60 NM.
&&

www.weather.gov/portland

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