High Wind in Washington, February 28, 2024

Area Forecast Discussion
National Weather Service Portland OR
236 PM PST Wed Feb 28 2024

.SYNOPSIS...Heavy valley rain and mountain snow will impact the area
Wednesday night into Thursday, before precipitation transitions to
scattered showers Thursday afternoon behind a cold frontal passage.
This will impact travel conditions along the Cascade passes and for
elevations above 1500 ft in the Coast Range. Gusty south winds will
also accompany the cold front Wednesday evening/night. A broad upper
level trough will then maintain cool and showery conditions Thursday
night into early next week. Snow levels will likely dip to around 500
ft during the overnight/morning hours this weekend, if not a bit
lower than that under heavier showers. Impactful snow is NOT expected
for elevations below 500 ft as temperatures will be too warm to
support accumulations beyond a dusting on grassy surfaces.

&&

.SHORT TERM...Wednesday evening through Friday night...At Noon
Wednesday, a warm front was continuing to lift northward into
northwest WA while an elongated cold front over the coastal waters
was gradually pushing eastward towards the coast. Northwest OR and
southwest WA were clearly in the warm sector between these two
frontal boundaries, resulting in widespread temperatures in the upper
40s to lower 50s and snow levels above 4500-5000 ft via webcam
imagery. Off-and-on light rain was also occurring within the warm
sector. Conditions will begin to deteriorate as the aforementioned
cold front over the coastal waters moves inland Wednesday
evening/night. The latest suite of hi-res model guidance continue to
suggest a swath of moderate to heavy stratiform valley rain/mountain
snow will accompany this front, which seems reasonable given the
strong frontogenesis in place. Precip rates will be orographically
enhanced for southwest-facing slopes as model soundings depict 50-70
kt sustained southwest winds between 900-700 mb. How much rain will
fall? Well, the NBM mean suggests another 1-1.5 inches of rain will
fall across the Willamette Valley, Cowlitz Valley, lower Columbia,
Portland/Vancouver metro, and at the coast between 4pm Wednesday and
4pm Thursday. Potential hydro impacts are discussed below in the
Hydrology discussion. QPF amounts are higher in the Cascades and
Coast Range at 2-3.5 inches, however this will fall in the form of
snow tonight into tomorrow as snow levels rapidly fall to around
1000-1500 feet by Thursday morning. This means anyone with travel
plans over the Coast Range and/or Cascade passes will need to be well
prepared for winter driving conditions as snow will be accumulating
quickly. In fact, the NBM is showing around a 50% chance for over a
foot of snow between 4pm Wednesday and 4pm Thursday at the Cascade
passes, except a 10% chance on US26 to Government Camp. Snow
amounts/probabilities are much lower for the Coast Range, however
still expecting 2 to 7 inches above 1500 feet in the Coast Range, and
even higher amounts above 2500 feet. This is still more than enough
for travel impacts.

It is also worth mentioning that gusty southerly to southwesterly
winds will occur along and ahead of the cold front. The latest
guidance still suggests wind gusts as high as 50-55 mph along the
central Oregon coast, and 30-45 mph for the north coast and most
inland locations. That said, localized gusts over 55 mph cannot be
completely ruled out along the central OR coast; the HREF is showing
a 20-40% chance for gusts over 55 mph between 7-11pm Wednesday. NBM
probabilities are a bit lower at 10-30%. While forecast wind speeds
are not quite high enough to warrant wind headlines, it's still worth
securing loose outdoor objects. Although widespread power outages are
unlikely, isolated power outages/tree damage will be possible. It's
always worth being prepared for a potential outage.

Stratiform precipitation will transition to scattered showers
Thursday afternoon/evening within the post-frontal environment.
Off-and-on showers will then continue Thursday night through Friday
night as a broad upper level trough remains over the region. Snow
levels will also dip to 500-1000 ft Friday morning and again Friday
night, and heavier showers will likely be able to briefly drag snow
levels down close to the valley floor. However, surface temperatures
should be several degrees above freezing and any snow that does fall
on the valley floor will tend to melt almost instantly. Therefore,
there is no need to worry about impactful accumulating snow on the
valley floor. Some locations will see a dusting of snow on grassy
surfaces at best. You will need to be driving over the Cascades
and/or Coast Range for significant travel impacts to occur. Concerns
for travel impacts along I-84 through the Columbia River Gorge are
low, as river level will likely see a rain/snow mix much of the time
with snow struggling to accumulate on the above freezing ground.

Lastly, the cold air aloft will also result in increasing instability
Thursday afternoon into Friday as SBCAPE values increase to around
100-300 J/kg. This should be just enough instability for an isolated
thunderstorm or two, mainly along and near the coast where
instability looks to be maximized. Any thunderstorm or stronger
shower that does form will have the potential to produce small hail
or graupel, as well as brief gusty winds. NBM thunder probabilities
peak between 15-30% along the coast/Coast Range, but fall to less
than 15% over the Willamette Valley.  -TK

.LONG TERM...Saturday through Tuesday night...The coldest
temperatures over the next seven days are expected to occur this
upcoming weekend when a trough axis associated with a broad upper low
will reside over the area, resulting in cool and showery conditions.
Models and their ensembles are in agreement for the trough axis to
shift eastward early next week, however western WA/OR will still be
under a cool and showery onshore flow regime as a shortwave trough
behind the trough axis dives southeastward down the B.C. coast into
the Pacific Northwest. Confidence for below normal temperatures is
high, as all four clusters from WPC's cluster analysis are showing
broad upper level troughing over the western CONUS Saturday into
early next week. With the colder airmass, snow levels will likely
bottom out around 400-500 feet Saturday morning and Saturday
night/Sunday morning. However, precipitation will be in the form of
off-and-on light showers, thus limiting snow accumulations for
elevations above 500 feet. Below 500 feet, any accumulating snow
beyond a quick dusting on grassy surfaces is highly unlikely as
temperatures will be several degrees above freezing. The probability
for 24-hr snow amounts on the valley floor is generally under 10%,
which seems reasonable given the showery onshore flow regime in
place. Given the time of year, wouldn't be surprised if graupel winds
up being more predominant than snow in the lowlands.  -TK

&&

.HYDROLOGY...Wednesday evening through Thursday...Widespread moderate
to heavy rain Wednesday evening into Thursday will result in rising
river levels. Minor flooding is possible along creeks and streams, as
well as in low-lying flood-prone urban areas. While the mainstem
rivers are not forecast to hit flood stage, there is a non-zero
chance a few rivers could hit minor flood stage. The latest HEFS
guidance is showing a 13% chance of minor flooding along the Nehalem
River near Foss, a 21% chance along the Wilson River near Tillamook,
a 15% chance along the Luckiamute River near Suver. Remaining rivers
in the area have around a 5% chance or less.

The best chance for river flooding will be along the Grays River near
Rosburg in Wahkiakum County. In fact, this is the only river that is
currently forecast to hit minor flood stage, but just barely. A Flood
Watch has been issued to cover this threat, and this will be upgraded
to a Flood Warning if confidence becomes high that the river level
will reach minor flood stage of 11.0 feet. If you encounter a flooded
road while driving, be sure to turn around as it is impossible to
tell exactly how deep the water truly is.  -TK

&&

.AVIATION...Low pressure over southern British Columbia will track
east while continuing to drive widespread rain and lower ceilings
across the Pacific NW over the next 24 hours. Coastal sites will
see a mix of MVFR and IFR conditions as the cold front approaches
tonight with a mix of VFR and MVFR inland. Southerly winds will
increase ahead of the front with wind gusts around 35-45 kts along
the coast and up to 30-40 kts will be possible this evening.
Winds will decrease quickly from north to south after frontal
passage between 06-09z Thursday. A deep moisture layer will
maintain variable ceilings into Thursday morning for all
terminals.

*NOTE: The observation out of KONP is generally limited to wind
 and pressure at this time. Periodically cloud cover, vis, and
 present wx are reported but are unreliable.

PDX AND APPROACHES... Predominately MVFR conditions with steady
rain. Ceilings will gradually lower directly ahead of the cold
front which is expected to move over the terminal around 06z
Thursday. Southerly wind gusts will peak this evening to around
30-35 kts and will diminish rapidly behind the front. -BMuhlestein

&&

.MARINE...An active weather pattern continues as a very large
scale Alaskan low brings multiple fronts across the coastal waters
through the weekend. Observations across the coastal waters and
along the coast in both Washington and Oregon show Gale force wind
gusts verifying as of 2 PM. The front is currently about 100 nm
offshore and is expected to cross the waters tonight roughly
around 10 PM. Strong southerly winds will compress along the
nearshore against the Coast Range and reach a peak of 45 kt for
areas south of Rockaway Beach. Steep wind driven seas will build
into the mid to upper teens during this time.

After frontal passage tonight, winds will remain out of the
southwest through Friday as the broad area of low pressure in the
Gulf makes its way southeast towards the Pacific NW. Winds will
diminish below Gale criteria but seas will remain steep and
hazardous through the weekend. There will be a brief period
Thursday afternoon in which seas will drop into the low teens but
will quickly build again as a 14-16 ft westerly swell coupled
with wind driven seas within a warm front Friday moves across the
waters. Combined seas will build towards 17 to 19 ft early Friday
and remain in the mid teens through the weekend. -BMuhlestein

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...Winter Weather Advisory from 10 PM this evening to 6 AM PST
     Friday for Central Coast Range of Western Oregon-Coast
     Range of Northwest Oregon.

     Winter Storm Warning until 6 AM PST Friday for Cascade Foothills

     in Lane County-Cascades in Lane County-Northern Oregon
     Cascade Foothills-Northern Oregon Cascades-Upper Hood River
     Valley.

WA...Winter Storm Warning until 6 AM PST Friday for South Washington
     Cascade Foothills-South Washington Cascades.

PZ...Gale Warning until 11 PM PST this evening 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.

     Hazardous Seas Warning from 11 PM this evening to 4 PM PST
     Thursday for Columbia River Bar.

     Hazardous Seas Warning from 11 PM this evening to 4 PM PST
     Friday for Coastal waters from Cape Shoalwater WA to Cape
     Falcon OR out 60 NM.

     Gale Warning until 2 AM PST Thursday 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.

     Hazardous Seas Warning from 2 AM Thursday to 4 PM PST Friday 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.

&&

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Preliminary Local Storm Report
National Weather Service Portland OR
1109 AM PST Wed Feb 28 2024

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1030 AM     Rain             4 ENE Cathlamet         46.22N 123.30W
02/28/2024  M1.70 inch       Wahkiakum          WA   Trained Spotter

            Measured 24 hour rainfall.

&&

ACB

Preliminary Local Storm Report
National Weather Service Portland OR
200 PM PST Wed Feb 28 2024

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0159 PM     Rain             4 ENE Cannon Beach      45.90N 123.87W
02/28/2024  M2.07 inch       Clatsop            OR   Trained Spotter

            Rainfall since midnight PST.

&&

Weagle