Gresham, Oregon 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

194
FXUS66 KPQR 211131
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
330 AM PST Thu Nov 21 2024

.SYNOPSIS...A few showers today, then rain returns tonight into
Friday along with another round of windy conditions Friday. Showery
weather followers over the weekend into next week.

&&

.DISCUSSION...Today through Wednesday...Satellite and obs show
vertically stacked low off the southern B.C. coast near 132W slowly
drifting to the northwest. The surface low at 971 mb at 06Z Thu is
forecast to gradually fill as it drifts to the northwest. To the
south and east of the CWA, persistent showers continue today. This
leaves the CWA with relatively lighter showers today, with a few
thunderstorms over the coastal waters.

Tonight rain returns as another storm system now just beginning to
develop near 37N/140W. This system supported by a 125-130kt jet will
rapidly deepen tonight as it swings to just inside 130W of the WA
coast Friday afternoon. Pressure drop with this storm will not be as
impressive as the recent meteorological bomb with about 18 mb drop in
24 hours. This system will bring another round of strong winds over
the coastal waters and at the coast.  As the low approaches winds
will be mainly easterly for breezy conditions at the coast and inland
near the Gorge tonight, then transition to southerly later in the
morning through afternoon. Strong southerly winds at the coast
potentially appearing late Friday morning through the afternoon as
the low track north off the WA coast. So have issued a High Wind
Watch for coast to affect the beaches and headland areas later Friday
morning into Friday evening. Will have to refine timing a bit.

Inland of the coast becomes windy as well on Friday, though appears
to be below any warning criteria. However winds in the Willamette
Valley and interior of southwest WA become gusty Friday. The mean NBM
24hr max gusts ending 10 pm Friday are in the 30-40 mph range, while
the 90 percentile shows 45-50 mph range. To slice it another way, the
probability of gusts exceeding 45 mph (wind advisory criteria) is 15
to 20%.

Rain will spread south to north tonight into Friday morning, with IVT
plume peaking around 500 kg/ms. Duration will be relatively short, as
the main stream of moisture only briefly crosses
into the area as the warm front sweeps north with the low.
Inland, 24h total QPF looks to be around 0.5-1.0" from 4 PM Thursday
through 4 PM Friday. Over the mountains and coast, QPF looks closer
to 1.25-2" during this time. Hydro impacts continue to look
minimal, with HEFS guidance showing less than 5% chance of minor
flooding for Coast Range rivers.

Snow levels rise above Cascades pass level today ahead of the
incoming system to around 7000-8000 feet tonight, so will have
another round of rain on snow to impact the snow pack. Snow levels
tumble Friday afternoon once the cold air wrapping around the low
pushes into the region. Snow levels drop to around 4500 ft Friday
afternoon, then to around 3000-3500 ft Saturday and Sunday. Snow
amounts during this time look to be around 1/2 foot at passes Friday
night to Sun day afternoon (48 hours), and closer to 1 ft for the
volcano peaks.

More benign conditions over the weekend into mid next week an upper
trough lingers over the northeast Pacific and Pacific northwest. This
will bring showers at times. Also there is a chance for thunderstorms
over the coastal waters and coast for the weekend. /mh

&&

.AVIATION...Predominately VFR conditions with isolated (10%-20%
probability) MVFR conditions with light showers and a 10%-15%
probability for thunderstorms beyond 30 nautical miles off the
OR/WA coast, through around 00Z Friday. Starting around 00Z
Friday, a low pressure system approaching from the southwest, will
bring increasing rain chances from south to north. South to east
winds will become more north to east with the approaching low,
with winds returning to a more south to east pattern towards the
end of the TAF period as the aforementioned low pushes northward
towards the Olympic Peninsula.

PDX APPROACHES...Predominately VFR conditions with isolated MVFR
conditions with light showers. Rain returns around 00Z Friday.
Southeast winds more easterly around 03Z Friday before becoming
southeasterly towards the end of the TAF period. /42

&&

.MARINE...A brief period of relatively calmer conditions through
today, but these conditions will be short lived as the next system
approaches from the south and moves northward parallel to our
coast. While there still remains some uncertainty in the exact
path of this low, guidance (both deterministic and probabilistic)
are in agreement that southerly gusts up 60 kt will manifest
across all waters. There will be about a 12-18 hour increase in
winds starting this afternoon with peak winds expected late
Thursday night and into Friday morning. Therefore, have maintained
the Hazardous Seas Warning through the majority of today with a
Gale Warning starting this evening. Also, have upgraded the Storm
Watch to a Storm Warning with a starting late tonight.

Elevated winds will also result in seas reaching the 19 to 22 ft
range late Thursday night/Friday morning and maintaining that
level through at least Friday night.

Conditions start to subside late Friday night/early Saturday and
winds and seas subside. Wind gusts are expected to fall below 25
kt by Saturday, with seas settling around 8 to 10 ft as well.
This subsiding trend is expected to continue into the start of
next week. /42

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...High Wind Watch from Friday morning through Friday evening for
     ORZ101>103.

     Winter Weather Advisory until 4 AM PST early this morning for
     ORZ126>128.

WA...High Wind Watch from Friday morning through Friday evening for
     WAZ201.

PZ...Hazardous Seas Warning until 10 PM PST this evening for PZZ210-
     251>253-271>273.

     Gale Warning from 10 PM this evening to 4 AM PST Friday for
     PZZ210-251>253-271>273.

     Storm Warning from 4 AM to 7 PM PST Friday for PZZ210-251>253-
     271>273.
&&

$$

www.weather.gov/portland

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