Aloha, Oregon 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

583
FXUS66 KPQR 130401 AAA
AFDPQR

Area Forecast Discussion UPDATED
National Weather Service Portland OR
801 PM PST Tue Nov 12 2024

...UPDATED for evening aviation weather.

.SYNOPSIS...A week of active weather ahead with a combination of
wind, rain, snow, and thunderstorms. Strong frontal system with
a coast jet will promote strong winds tonight into Wednesday
morning with the highest speeds along the coast. Wind Advisory
and High Wind Warnings in effect through Wednesday morning.
Heavy rain expected which, when combined with the fallen leaves
and clogged drains could lead to localized urban flooding. In
Wednesday also will bring increased chances for thunderstorms
with the chance for waterspouts near the coast.
&&

.SHORT TERM...Now through Wednesday Night...A strong area of low
pressure drops down from the Gulf of Alaska which will bring a
variety of weather based concerns to the region. The first main
concern is wind late tonight into Wednesday morning. This
front`s pressure gradient is strong and is associated with a
multi-layered jet. Looking at forecast model soundings, winds
around 4000 ft AGL are around 50+ mph. These winds will likely
mix down along the coast with the energy of the system. High
Wind Warning is in effect for the coastal areas with gusts up to
60 mph expected. The hi-resolution guidance has "backed off" a
bit in regards to the peak wind speeds, but the 90th percentile
of the HREF still is producing 65+ mph winds along the Central
Oregon Coast. Winds will also be elevated along the Cascades and
the Willamette Valley. While the valley will not see nearly as
strong of winds due to it`s proximity to the jet, gusts are
still high enough to near 45 mph. The main impact is going to be
the potential for downed trees due to them being water soaked
and covered in leaves still. While winds will decrease in the
afternoon on Wednesday, conditions will remain breezy.

The next sensible weather feature is rain. While river flooding
is highly unlikely (<5% chance for any given river to reach
minor flood stage according to the latest HEFS guidance), there
is a higher risk for urban flooding in low-lying areas with poor
drainage. Given many storm drains are currently clogged up with
leaves, hourly rain rates around 0.2 in/hr or higher will be
enough to cause some issues in flood- prone areas. The UWWRF and
the HRRR both show hourly rain rates peaking between 0.2-0.4
in/hr around 0500 Wednesday. These higher rain rates will be
topography driven and whether or not thunderstorms form. The
best chance for urban flooding will occur Tuesday night through
Wednesday. If you encounter a flooded road when driving, be
sure to turn around if possible as it is impossible to tell
exactly how deep the water may be. Be sure you have a way to
receive NWS advisories and warnings and remember - turn around,
don`t drown.

Now onto the thunderstorm potential. The Storm Prediction Center
has put the coastal areas under a "marginal risk" of
thunderstorms. Based on the forecast soundings, will have skinny
but ample CAPE, and speed and directional wind shear. Have
increased chances of lightning to 15-30% with the highest
probability along the Coast. While initially the morning looked
to be the time frame of the highest potential, the conditions
have extended through the afternoon. These storms will bring
locally higher rainfall amounts, gusty winds, and the potential
for rotation.

There are also concerns for high surf conditions and minor tidal
overflow flooding at the coast with the upcoming Perigean Spring
tides. For more details on these hazards, please refer to the "Beach
Hazards" section below. -Muessle/TK


.LONG TERM...Thursday through Tuesday...The long term forecast
is highlighted by a cool and showery weather pattern typical of
mid-November. WPC`s cluster analysis for 500 mb heights and
anomalies suggests excellent agreement between the GEFS/EPS/CMC,
showing an upper level trough over the coastal waters late
Thursday shifting inland over the western CONUS Friday. At 500
mb, there is a weak ridge attempting to build in but it is
unsupported at the surface. Even with this being the case,
northerly flow will dominate and cannot rule out clearing skies
though which will support much cooler overnight lows. The
probability for low temperatures near freezing overnight Friday
into Saturday morning have seen little change. For rural areas
of the inland valleys, there is around a 50% chance of below
freezing temperatures. Near Eugene is around 70-80%. Probabilities
are around 60-700% for the valleys of the Cascade Foothills
around Sweet Home, Creswell and Molalla. The greater Portland-
Vancouver metro area still has less than a 5% chance for below
freezing temperatures.

This cooler and drier pattern will quickly come to an end as the
flow becomes zonal on Sunday with increasing onshore flow. This
onshore flow will send a Pacific frontal system inland bringing
more significant rain amounts late in the weekend. That being
said, expecting minimal impacts with this system as winds do not
look significant and ensemble guidance for QPF suggest rain
amounts will not be high enough for hydro concerns.

Weak ridging attempts to build in once again early next week but
will be difficult to overcome the pervasive troughing from this
last week. However, more and more model ensemble guidance is showing
a transition to strong offshore flow middle to late next week,
bringing the potential for gusty east winds along with dry weather.
Will need to watch how model guidance evolves over the coming days as
uncertainty is currently high. -Muessle/TK

&&

.AVIATION...No changes overall. Rain with VFR inland this evening,
with mix of MVFR and VFR along the coast. Satellite showing
developing low pressure off the south Oregon coast. As such, this
will likely slow the arrival of gusty south winds across the
northern TAF sites. Will adjust 06Z TAFs to show this, with east
winds likely to persist near PDX/TTD til front arrives (12Z to 14Z).
Expect CIGS to hold at lower VFR until after midnight, then lower to
MVFR overnight. Not much change through Wed am, but will see rain
changing to showers and a few thunderstorms after the front shifts
inland Wed am.

Main concern will be gusty south winds along the coast overnight,
and inland for a time later tonight into early Wed am. Generally,
surface winds gusting 50 to 60 kt along the coast, with 35 to 45 kt
inland. Winds will ease behind the front, around 12Z to 14Z on coast
and after 15Z inland.

PDX APPROACHES...Rain with lower to mid-range VFR until 08Z, with
east winds 10 to 15 kt. After 08Z, will see CIGS gradually lower
back to MVFR as rain increases. Surface winds remain easterly til
front arrives (around 13Z to 14Z), then will become gusty from
south. But, winds to west and south of the airport will be southerly
and gusty earlier. Expect turbulence, with modest east winds 40 to
50 kt at and above 2000 AGL from 10Z to 16Z Wed.

&&

.MARINE...Headed into this evening a strong frontal system slated
to push into the coastal waters with southerly winds quickly ramping
up and peaking overnight - high confidence in Storm Force (>48 knot)
gusts. A coastal jet is also likely going to set up tonight, with
winds just above the surface(500-1000 ft) pushing 70 knots. Should
these winds get mixed down towards the surface as the front passes,
it is possible (30-40% chance) for some gusts closer to 65 kt. Seas
are expected to become very steep and chaotic, likely 20 to 25 ft
again overnight as a fresh southerly swell also develops driven by
the aforementioned wind.

Behind the frontal boundary seas are expected to subside into the
mid to upper teens by Wed afternoon but winds gusts remain near 30-
35 knots into the early evening. It`s worth noting weather
conditions remain active through Wednesday with another round of
thunderstorms possible (20-40% chance) into Wed night, any of which
could produce erratic wind gusts, lightning, and even a few isolated
waterspouts.

Westerly winds will continue to ease through Thursday, while another
mid-period westerly swell moves into the coastal waters at 14 to 17
feet around 15 seconds. Once this swell passes the wave state
finally calms for the second half of Friday into Saturday with
significant wave heights dipping below 10 feet. However we`ll need
to watch another weather disturbance expected to arrive late Sunday
into Monday bringing another round of active weather.
-Schuldt/DH

&&

.BEACH HAZARDS...A High Surf Advisory remains in effect until 4pm
today (Tuesday) with westerly swells driving breakers up to 20 to 25
feet. This high surf will affect beaches, producing rip currents,
sneaker waves and beach erosion. Remain alert for exceptionally high
waves and stay a safe distance from the water`s edge.

A strong weather system on Wednesday will bring the possibility of
tidal overflow and minor coastal flooding during high tide Wednesday
morning into the mid afternoon hours, especially for the northwest
Oregon coast and southwest Washington coast where a Coastal Flood
Advisory is in effect. And while unrelated to the current series of
weather disturbance, the perigean spring tides, also known as king
tides, will begin Friday November 15, increasing high tides. Will
continue to monitor total tides along with the response of local
rivers along the coast this week.

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...High Wind Warning until 6 AM PST Wednesday for ORZ101>103.
     Coastal Flood Advisory from 7 AM to 1 PM PST Wed for ORZ101.
     Wind Advisory until 6 AM PST Wednesday for ORZ108>111-114>118.

WA...High Wind Warning until 6 AM PST Wednesday for WAZ201.
     Coastal Flood Advisory from 7 AM to 1 PM PST Wed for WAZ201.
     Wind Advisory until 6 AM PST Wednesday for WAZ204>206.

PZ...Storm Warning until 7 AM PST Wednesday for PZZ210-251>253-
        271>273.
     Hazardous Seas Warning from 7 AM Wednesday to 4 AM PST Thursday
        for PZZ210-251>253-271>273.
&&

$$

www.weather.gov/portland

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