NWS Portland, OR wrote its last area forecast discussion before the first event at Dec 26, 8:42 PM PST, 1 hour earlier.
Area forecast discussion, Dec 26, 8:42 PM PST, 1 hour before
Area Forecast Discussion...UPDATED
National Weather Service Portland OR
842 PM PST Mon Dec 26 2022
Updated Aviation/Marine/Beach Hazards sections
.SYNOPSIS...A series of Pacific frontal systems will bring wet and
occasionally windy conditions to the region throughout the upcoming
week. Tonight and Tuesday will be particularly stormy as strong low
pressure brushes the Pac NW coast. Subfreezing air trapped in the
central Columbia Gorge and Hood River Valley will result in freezing
rain tonight. Then stronger westerly winds should finally scour out
the cold air Tuesday. Strong winds are likely for much of SW
Washington and NW Oregon later tonight into Tuesday. Snow levels
will remain high through tonight, then should lower to the Cascade
passes on Tuesday. Additional systems will follow, bringing more
bouts of rain and Cascades snow. A less active weather pattern sets
up for the weekend.
&&
.SHORT TERM...Tonight through Thursday...Deepening low near 44N/138W
already beginning to occlude with warm front extending to northwest
Oregon. This low will track to just off the central or north WA
coast around midday Tuesday with forecast central pressure around
970-975 mb per deterministic models. EPS ensemble members show low
centers clustering on the north WA coast, while GEFS members are
slightly south of that. Overall pretty good agreement.
Winds - High Wind warning out for the coast/coastal mountains with a
Wind Advisory for the interior lowlands (Willamette, southwest WA.)
Southerly 850 mb winds pick up to 70-90 kts tonight with as the cold
front approaches. NAM indicating 60-70 kt just up to the coastline at
925 mb tonight. So current forecast of gusts to 80 mph at the
beaches, and 60-70 mph gusts for other areas at the coast. Will
continue with the Wind Advisory for the interior lowlands, but will
be at the high end of advisory level. So will definitely see impacts
such as downed trees and resulting power outages. The bent-back
occlusion and its associated sting jet will likely slap the north
coastal zones Tuesday morning, depending how close the low center is
to the forecast area.
Temperatures now above freezing in the central Gorge and Hood River
Valley but should see temps dip to freezing this evening. So will see
freezing rain continue tonight with limited cold air in the lower
Columbia basin, as well as the cold air mass moderating temperatures
late tonight.
Cool onshore flow behind Tuesday morning's front will cause showers
to persist through Wednesday. With 00z GFS 850 mb temps down to
around -2 deg C, can expect snow levels to lower to around 3500 feet.
The Cascades could rack up several inches of snow Tue night into Wed
but with snow ratios on the low side, looks marginal for winter
headlines there. And the active weather doesn't stop there...
additional frontal systems are likely to keep our weather active
through the end of the work week. /mh Weagle
.LONG TERM...(THURSDAY NIGHT THROUGH MONDAY)...
The strong jet across the northeast Pacific remains directed at the
Pacific Northwest begins to buckle on Friday as the jet stream splits
and heads into California. As a result will see a trend to less
stormy weather through the weekend. May even see a dry day Sunday.
With the jet stream heading south of the region, the PacNW will be in
the cool side of the jet with snow levels wavering around 3000 to
4000 ft, so incoming weather systems will bring accumulating snow to
the Cascades. NCEP 500 mb clusters are is good agreement so feel
moderately confident in the upcoming changes. The PacNW will be on
the cool side of the jet through early next week with snow levels in
the 3000 to 4000 ft range for the most part, so will see accumulating
snow in the Cascades.
&&
.HYDROLOGY...In the near term - The stalled warm front over the
coast/coast range of northwest Oregon to just east of the Willapa
Hills in SW WA this afternoon. Have adjusted QPF for this afternoon
with rain rates around 0.1 to 0.2 tenths per hour. Expect to see
another inch or so through late afternoon. The front will then begin
to lift north tonight, increasing rain over southwest WA. Rain will
increase tonight with the approach of the next storm.
Flood warning on the Grays River continues but currently getting a
bit of a break in the rain, but renewed moderate to heavy rain
tonight should bring it up to flood stage. As a result of the
changes and new QPF forecast, have issued a Flood Watch for the coast
and coast mountains in northwest Oregon/southwest Washington for
tonight through Tuesday night. Current forecasts so the Wilson River
near Tillamook and Nehalem River near Foss approach flood stage
Tuesday afternoon. Also flooding of creeks and other flood prone
areas is possible tonight. Also with initial southerly winds may
target the Nehalem River basin more than some others, due to how that
river and its headwaters are situated.
Overall, we can expect around 1 inch for the inland valleys, 2 inches
for the coast, and 3-5 inches of rain for the higher terrain.
&&
.AVIATION...06Z TAFs: Mostly a mix of MVFR and VFR as of 0430Z,
with VFR most prevalent over the south interior. A strong frontal
system will move inland late Monday night and would expect
predominant MVFR conditions by 12Z. The front will push across
the region later Tue morning, but little improvement in conditions
through the day. However, chances for VFR look to improve in
the 00Z to 06Z Wednesday time frame in the post-frontal air mass.
South wind will increase overnight, except for the Columbia River
Gorge where persistent east wind 20-30 kt with gusts 40-50 kt will
continue. LLWS potential will increase for KTTD and KPDX
overnight, with surface east to southeast wind and forecast south
wind 45-55 kt at FL020. Gusts 50-65 kt can be expected for the
coastal areas 12Z Tuesday through at least 00Z Wednesday. Gusts
35-45 kt will occur in the interior valleys Tuesday morning
into the evening. LLWS potential will be most prevalent through
around 18Z Tuesday. Southwest wind will finally push through the
Columbia River Gorge Tuesday afternoon.
For detailed Pac NW aviation weather information, go online to:
http://weather.gov/zse
KPDX AND APPROACHES...VFR at the terminal as of 0430Z. However,
expect conditions to fall into MVFR overnight as the next frontal
system spreads inland. Areas of IFR are likely late Monday night
through Tuesday morning, especially in the Tualatin River Valley.
Improvement to VFR looks possible in the 00Z to 06Z Wednesday
period. East to Southeast surface wind 15-20 kt with gusts to 30
kt will persist at the terminal and east to the west end of the
Gorge through about 15Z Tuesday. LLWS is highly likely, with
forecast south wind 45-60 kt at FL020. Wind shifts to the south at
the terminal around 15Z, but not until 16-18Z at KTTD. Southerly
wind gusts 35-45 kt can be expected Tuesday morning through early
evening. Weishaar
&&
.MARINE...Monday evening satellite imagery revealed a rapidly
deepening low pressure area near 45N 130W. This low is forecast to
make landfall along the south Washington coast around 10 AM
Tuesday. Models remain in good agreement showing a central
pressure around 965 mb 4 AM Tuesday, with the low center just
inside 130W. The low appears to be tracking a little ahead of the
model guidance. The central pressure is expected to be around 975
mb upon landfall. There will be two peak wind periods. The first
is forecast to occur between 10 PM tonight and around 2 AM
Tuesday. Models show boundary layer wind wind speeds 45 to 55 kt
with this first round. The wind eases a bit late tonight and then
ramps up again as the bent-back occlusion swings through the
waters and then shifts inland. The strongest wind speeds look to
occur between 8 AM Tuesday through mid-afternoon Tuesday. Storm
force wind gusts first develop over the far south waters and then
spreads to the remaining waters by mid-morning. Some models are
suggesting peak boundary layer wind speeds on the order of 55-65
kt. Believe these speeds may be bit overzealous, but 45-50 kt
sustained speeds not out of the question. Wind speeds diminish to
high-end small craft advisory levels late Tuesday evening.
At 8 PM Monday evening, buoy reports indicated seas as high as 23
ft. Wave guidance continues to indicate seas to 30 ft Tuesday,
with breakers to 40 ft. Seas will slowly subside Tue night into
Wed, with seas dropping back under 20 ft early Wednesday.
While rest of the week remains active, do not anticipate wind or
seas as high as Tuesday. That is, expect periods of 20 to 25 kt
wind, mainly with the front on Thu, while seas stay mostly in the
lower teens through Sat. Weishaar
&&
.BEACH HAZARDS...Very hazardous conditions can be expected along
the beaches. Breakers to 40 ft on gentle to moderate beach slopes
will be possible Tuesday through Tuesday night. The combination of
extremely large waves, very high tides, a 2.5 to 3.0 ft surge/tidal
anomaly and high river flows has the prompted the issuance of a
Coastal Flood Warning for the south Washington coast. The forecast
high tide Tuesday afternoon for Toke Point is 9.6 ft. Up to a 3.0
surge/anomaly is expected, producing a total tide closer to 12 ft.
Will continue with the Coastal Flood Watch for the Oregon beaches
as confidence reaching warning criteria is not quite as high.
Weishaar
&&
.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Flood Watch through late Tuesday night for Coast Range of
Northwest Oregon-North Oregon Coast.
High Surf Warning until midnight PST Tuesday night for Central
Oregon Coast-North Oregon Coast.
High Wind Warning until 7 PM PST Tuesday for Central Coast
Range of Western Oregon-Central Oregon Coast-Coast Range of
Northwest Oregon-North Oregon Coast.
Coastal Flood Watch from 6 AM PST Tuesday through Tuesday
evening for Central Oregon Coast-North Oregon Coast.
Wind Advisory from 2 AM to 7 PM PST Tuesday for Central
Willamette Valley-Greater Portland Metro Area-Lower
Columbia-South Willamette Valley.
Winter Weather Advisory until 4 AM PST Tuesday for Central
Columbia River Gorge-Upper Hood River Valley.
WA...Flood Watch through late Tuesday night for South Washington
Coast-Willapa Hills.
Wind Advisory from 2 AM to 7 PM PST Tuesday for Greater
Vancouver Area-I-5 Corridor in Cowlitz County.
Winter Weather Advisory until 4 AM PST Tuesday for Central
Columbia River Gorge.
High Wind Warning from 5 AM to 7 PM PST Tuesday for South
Washington Coast-Willapa Hills.
Coastal Flood Warning from 6 AM to 10 PM PST Tuesday for South
Washington Coast.
PZ...Gale Warning until 1 AM PST Tuesday for Columbia River Bar.
Storm Warning from 1 AM to 4 PM PST Tuesday for Columbia River
Bar.
Gale Warning until 10 PM PST this evening for coastal waters
from Cape Shoalwater WA to Florence OR out 60 nm.
Storm Warning until 7 PM PST Tuesday for coastal waters from
Cape Shoalwater WA to Florence OR out 60 nm.
&&
www.weather.gov/portland
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