Heavy Snow in Oregon, March 19 to 20, 2025

Area Forecast Discussion...UPDATED
National Weather Service Portland OR
800 PM PDT Wed Mar 19 2025

Updated Watches/Warnings/Advisories and Marine Discussion

.SYNOPSIS...The complicated and messy pattern continues as a
frontal boundary sets up over the ocean. A series of fronts push
inland through early Saturday morning, each producing rain, and
heavy snow over the Cascades. Rain continues on Sunday with as
a stronger front moves over the region, but targeted over the
Canadian islands and Alaska Panhandle. High pressure builds
early next week leading to warm and dry conditions on Monday and
Tuesday.

&&

.SHORT TERM...Now through Saturday Night...To quickly summarize
the next several days: wet, rainy, and snowy. There are a series of
systems that will move over the region through Saturday, each with
the promise of precipitation - either as rain and/or snow. The
main source of active weather is a low pressure system that is
moving throughout the northeast Pacific. The low is currently
over Haida Gwaii and the occluded front is draped across the
coast into northern California. This front will slowly move
inland as the low shifts over the Alaska Panhandle. As it does
so, colder air that is wrapped around the low will push in
behind the front causing snow levels to drop to near 3500 ft.
Heaviest precipitation will occur over the coast and Coast
Range, and then orographically lifted over the Cascades.

As this initial wave departs to the east, a second shortwave will
move in quickly behind it, bringing increased precipitation coverage
through much of the overnight period. Mid-level cooling will allow
for modest instability overnight, which could allow a few convective
post-frontal showers to produce brief heavy downpours and maybe a
lightning strike or two. Chances are highest along the coast.
This secondary feature may actually be responsible for more of
the high-terrain snow accumulations as its increased
precipitation amounts coincide with the lower snow levels.

Have upgraded the Winter Weather Advisory to a Winter Storm
Warning through late Thursday/early Friday morning. The bulk of
the heaviest precipitation will be with the second wave between
1-11 AM Thursday. Throughout its entirety, significant snowfall
accumulations of 2-4 feet are likely above 4500-5000 ft and 8-14
inches down to around 3500 ft. At lower elevations, total
rainfall of 1-2 inches is expected along the I-5 corridor, with
higher amounts of 2-4 inches in coastal areas, the Coast Range
and Willapa Hills, and the Cascade foothills.

The third frontal system is moving a bit faster than previously
forecast blending nicely into the first two disturbances. This
front, while precipitation wise is stronger, is associated with much
warmer air. This has caused snow levels to rise above pass level.
Wet bulb 0 deg C temperatures will remain above 4500 feet through
the day on Friday. Right now, this third frontal system on Friday
will have less snow and is trending towards advisory level
accumulations above 4000 feet. But, if snow levels do not rise
considerably, warning level snow is possible yet again.
There is less than a 30% chance of snow greater than 12 inches below
5500 ft so have not issued any watches at this time. Will have to
continue to evaluate as the systems move through as confidence is
incredibly low. Post frontal showers persist through Saturday.
												-Muessle/Picard

.LONG TERM...Sunday through Tuesday...Sunday becomes a
bit more convoluted as the jet stream ridges aloft, but low level
moisture and a warmer airmass moves in. Global models suggest a
surge of precipitation associated with a weak atmospheric river to
the north. This system will produce a significant amount of
precipitation, but it is trending to the north. In Pacific county,
rainfall totals may range from 0.15-2.25 inches for 24 hour rainfall
ending at 5 AM Monday. Right now there are select rivers with less
than a 20% chance of rivers going into Action Stage on Sunday. This
does not appear to be widespread and is generally isolated to our
more triggery rivers, but cannot rule out some rising river levels.

Now if you're craving some sun, Monday and Tuesday will be the days
for you! High pressure is going to build which will bring in warmer
and drier air from the south. Models are suggesting a thermal trough
developing along the coast which will enhance easterly flow. To
paint the picture for this scenario, 850 mb temperatures will rise
to around 14 deg C. Within the Willamette Valley, temperatures will
range from around 70 deg F to almost 78 deg F (10th to 90th
percentile). The coast will see less fluctuation in those
temperatures staying in the mid 60s. 				-Muessle

&&

.AVIATION...A frontal system is moving into the area late this
afternoon with steadier rain breaking to showers this evening.
Going forward into the Thursday morning we'll see a 50-70% chance
for MVFR CIGs/VIS for coastal terminals and 20-35% for inland
terminals. Winds will be breezy as well with gusts around 20-30
knots at the coast and 15-23 knots inland, decreasing later
overnight into Thursday morning. Lingering shower activity
persist through Thursday with guidance suggesting increasing
likelihood for MVFR CIGs at all inland and coastal sites after
16-18z Thursday. -Schuldt

PDX AND APPROACHES...Expect mostly VFR conditions through the
evening and overnight hours although there is a 20-30% chance for
high end MVFR CIGS during this period. Rainfall likely arrives
right at the start of the TAF period, breaking to showers this
evening. Confidence is higher in more prominent MVFR conditions
late Thursday morning through the rest of the day. 		-Schuldt

&&

.MARINE...Seas sharply build into the mid to upper teens through
the evening hours largely driven by wind waves/fresh swell. Given
the significant waves heights around 11-14 feet and short periods
around 11-13 seconds a Hazardous Seas Warning is in effect for the
inner and outer waters through Thursday evening. By Thursday
afternoon, seas will decrease back towards 10-13 feet at 12 seconds.
However yet another frontal system is expected to arrive late
Thursday into Friday bringing a moderate likelihood (40-60%) for
gale force winds. These winds likely drop below Gale force by midday
Friday. From there the storm track will slowly shift to our north
over the weekend followed by a period of calmer weather and
northerly winds early next week. /42-Schuldt

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...Winter Storm Warning until 11 PM PDT Thursday for ORZ126>128.

WA...Winter Storm Warning until 11 PM PDT Thursday for WAZ211.

PZ...Small Craft Advisory until 8 PM PDT Thursday for PZZ210.

     Hazardous Seas Warning until 8 PM PDT Thursday for PZZ251>253-
     271>273.

&&

www.weather.gov/portland

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