789
FXUS66 KPQR 091045
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
345 AM PDT Mon Mar 9 2026

.SYNOPSIS...

&&

.SHORT TERM...Now through Wednesday Night...The initial stages of
an incoming cold front are beginning to make landfall with
showers popping up over the area. Rainfall totals have been
minimal thus far, but with the showery nature of the
precipitation, will see isolated areas of higher accumulation.
The frontal movement will promote orographically driven rainfall
accumulations with the Coast Range and Cascades seeing the
highest amounts. The Willamette Valley sits within the rain
shadow and will likely see less rain. We are expecting this
round of rain to persist through Tuesday. In conjunction with
the rain, a cold airmass is moving in from the north as a cold
air wrapped low in the Gulf of Alaska drops southward. This cold
air will cause snow levels to drop to around 1500-2000 ft today
and lower even further overnight into Tuesday closer to 500 ft.
Modeled 850 mb temperatures sit around -5 to -7 deg C which is
slightly warmer than previously expected. However, that is cold
enough to make sure that precipitation that is produced over the
Cascades falls as snow. A Winter Weather Advisory remains in
effect through Tuesday afternoon for this specific system.

For the lowlands, things become a bit more complicated as we
will need to have the perfect match up of cold air to
precipitation...timing will be everything. Currently there
remains anywhere from a 10-20% chance of lower elevation
accumulating snowfall (below 500 ft) within the Portland-
Vancouver Metro Area, and around a 30% chance in the higher
elevations like the West Hills. For the Cowlitz County Lowlands,
chances for any accumulating snow remains around 40-60% but
much lower for 1 inch or more where those probabilities are in
the teens. Ultimately, confidence is low on any accumulating
snow there. The Coast Range is complicated as well as it sits
right along the snow level elevation for the time frame in which
we will see the most precipitation. Areas most at risk for
advisory level snow (2" or more) remains in the Willapa Hills
and the north Oregon Cascades. When looking at the spread of
probabilities though, there is anywhere from a 10-60% chance for
2" depending on what model you look at. Highest confidence lies
in the peaks of the range, while the valleys and many of the
commute ways are right around a 20-40% chance. Higher
resolution models are not showing nearly as high of
accumulation.

As the low pressure system in the Gulf of Alaska shifts inland
over British Columbia, High pressure off of the coast of
California will amplify. This pattern shift will usher in warmer
air that is associated with a weak atmospheric river.
Precipitation amounts will increase once again but, as has been
the trend, just how much we will see and what type is still
under evaluation. With the warm air moving in, snow levels will
rise to 3500-4000 ft by Wednesday morning isolating any snowfall
chances to the Cascades from pass level up. The south Washington
Cascades though will hold on to the cold air longer though with
snow levels remaining around 2500 ft until Wednesday afternoon.
Based on current guidance from the Warning Prediction Center
(WPC) and models, there is an increasing probability for Winter
Storm Warning level snowfall on Wednesday - mainly for the south
Washington Cascades. The probability of these accumulations is
around 30-60% so have issued a Winter Storm Watch at this time.
Confidence is low as again, timing will be everything. Will the
heaviest precipitation time up with the lingering cold air or
will the warmer airmass move in first and push the precipitation
further northward. We will continue to evaluate, but as it
stands, the peak potential timeframe for impactful snowfall
will be Wednesday morning. Other portions of the Cascades have
less than a 10% chance of Warning level snowfall aside from the
peaks and resorts.

Wednesday will also see a southerly wind reversal which will
bring gusty conditions to the area - especially along the coast.
There remains high uncertainty in exact speeds as it will be
driven by the pressure gradient. One thing to note though if
looking at some of the models, because we have seen breezy
easterly winds over the last month, some models are experiencing
what we call a strong "east wind bias". Because of this,
forecast wind speeds may be on the high side. For example, in
the Columbia River Gorge at Cascade Locks, the mean forecast is
a gust of 53 mph, the 25th percentile at 44 mph, and the 75th
percentile at 62 mph. However, a southerly wind is very
difficult to get into Cascade Locks and therefore getting wind
speeds in the 50s will be difficult. Instead have trended
towards the 10th percentile for the Columbia River Gorge. -27


.LONG TERM...Thursday through Sunday...Transitioning into later
in the week, precipitation will continue with warm air lingering
over the area. The bulk of the precipitation will stream to the
north with the jet stream. Heavier rain potential remains high
on Thursday into Friday where the mean 24-hr precipitation
totals ending Friday morning are around range from 2.0-2.5" of
precipitation in the south Washington Cascades and 1.5-1.9"
along the north Oregon Coast Range. Inland within the Willamette
Valley there is anywhere from 1.0-1.25" in Portland to 0.2-0.4"
in Eugene. If the atmospheric river that sits over Washington
shifts southward, we could see more impactful rain - especially
along our more susceptible Coast Range and Willipa Hills
rivers.

On Friday, some models are attempting to shift the Atmospheric
River further south which puts us in a borderline wet vs dry
scenario. In general, the ECMWF favors a wetter solution overall
on Thursday night into Friday. It is not clear yet whether the
heavier rain will end Thursday night, Friday, Friday night, or
Saturday. As such, there is still a very large degree of model
spread in regards to total rain amounts. Depending on how
quickly precipitation falls over a given watershed or urban area
and the duration of precipitation, these higher end solutions
could result in some river flooding and urban flooding (however
this would represent the worse case scenario with a 10% chance
of occurring; HEFS guidance for river flooding backs this up and
shows probabilities under 10%, and under 5% for slower-
responding rivers). Lower to middle end QPF solutions would
result in no hydro concerns at all. As of right now, the most
likely outcome is for minimal to no flooding concerns, however
this system will need to be monitored closely over the coming
days.

Heading into next weekend, uncertainty increases regarding exact
temperatures and precipitation amounts. 500 mb heights show two
potential scenarios with half of the clusters favoring a wetter
solution, and half a drier outcome. The same rings true for a
warm vs cooler scenario. An example of this difference lies in
Salem where the 10th to 90th percentiles for maximum temperature
on Saturday show a range of 49 deg F to 61 deg F...an 11 degree
spread. There is less of a discrepancy as you move further
north. Sunday though brings even higher uncertainty with the
10th to 90th percentile in Portland ranging from 45 deg F to 61
deg F. In Eugene, the maximum temperature spread ranges from 48
deg F to 69 deg F; nearly a 20 degree difference. This helps
show just how much uncertainty lies in the long term forecast.
Ultimately, it comes to how strong the high in the Pacific
builds, the jet tracking north or south, and just how much of
the warm air we will see. -27

&&

.AVIATION...Predominately VFR with light and variable winds
becoming northwesterly through the day. Light showers in the
area are present, but for most terminals they have yet to
manifest and instead are getting hung up along the Coast Range.
In the heavier rain though, CIGs are MVFR. Climatologically,
conditions will trend to be low end VFR through the next 24
hours. One thing to note for preparations is that temperatures
are going to cool significantly after 06Z Tue. We are expecting
widespread freezing or near freezing temperatures at many of
our inland main airports. Because of this, if skies remain clear
and winds light we cannot rule out frost formation. The highest
probability would be south of KSLE. In the north, there is
around a 20% chance of low-elevation accumulating snow which
would impact KPDX, KHIO, and KTTD. For sites like KSPB and KKLS,
those chances for 0.1" or more of snow rises to around 40%.
Warm ground temperatures leading up to this incoming
precipitation will help limiting significant accumulation.

KPDX AND APPROACHES...VFR conditions through most of the
forecast with around a 40-60% chance of MVFR CIGs after 10Z Tue
with an incoming front. Moderate temperatures during the day
will cool to around freezing overnight. 10-20% chance of
accumulating snow after 10Z Tue. Light northwesterly winds.
-27

&&

.MARINE...Conditions remain elevated in regards to wind as a
frontal system in the Gulf of Alaska continues to drop
southward. Overall, winds have bounced around quite a bit
with gusts ranging from 17-25 kt. Seas have remained steady at
7-9 ft at 13 seconds. This morning we will see a brief lull in
winds but seas will quickly build. Combined seas of 9-11 ft are
expected this afternoon and will spread to encompass all of the
waters. Have expanded the Small Craft Advisory to account for
the building seas in the southern and inner waters. The Columbia
River Bar has a low probability of being impacted until Tuesday
as the ebb reaches 10 ft in the morning.

A secondary low pressure system and accompanying warm front
will skirt over Vancouver Island on Wednesday increasing the
north-south pressure gradient. A southerly wind reversal is
expected and followed by a substantial increase in both
sustained winds and gusts. Confidence has decreased slightly in
Gale Force Wind potential Wednesday afternoon and evening with
the NBM projecting a 30-40% chance for hourly wind gusts to
exceed 34 knots during this period. The main time frame of
concern looks to be Wednesday afternoon. The overall coverage
remains uncertain at this time as it looks to mainly impact the
central waters of PZZ252/272. Have decided against issuing a
Gale Watch at this time, but there is a very high probability
that one may be issued in the coming forecasts.

Seas are likely to respond as well, rising up into the 14-17 ft
range at 10-11 seconds which would lead to a Hazardous Seas
state. At least a coastal jet is not forecast, but wind gust
speeds will hover right around 34-40 kt. Due to stronger winds
aloft, they could mix down and areas around the Columbia River
Bar have around a 10% chance of wind gusts of 50 kt or greater.
Conditions gradually settle down Thursday through the end of the
week but the overall pattern remains active moving forward.
-27/99

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Winter Weather Advisory until 5 PM PDT Tuesday for ORZ126.
WA...Winter Weather Advisory until 5 PM PDT Tuesday for WAZ211.
     Winter Storm Watch from Tuesday afternoon through Wednesday
     afternoon for WAZ211.
PZ...Small Craft Advisory from 8 AM Tuesday to 8 AM PDT Wednesday
     for PZZ210.
     Small Craft Advisory from 8 PM this evening to 8 AM PDT
     Wednesday for PZZ251>253-273.
     Small Craft Advisory until 8 AM PDT Wednesday for PZZ271-272.
&&

$$

www.weather.gov/portland

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