165
FXUS66 KPQR 081745 AAA
AFDPQR

Area Forecast Discussion...UPDATED
National Weather Service Portland OR
945 AM PST Fri Nov 8 2024

Updated Aviation Discussion

.SYNOPSIS...Weakening high pressure will bring one more dry and
mild day ahead of an approaching system. More active weather returns
this weekend, with several rounds of rain bringing potential hydro
issues early to mid next week. Lowering snow levels will bring
accumulating snow back down to the Cascade passes MOnday into
Tuesday.

&&

.DISCUSSION...Satellite imagery and surface observations from around
the region show another mostly clear and chilly night across much of
northwest Oregon and southwest Washington as high pressure remains
in control over the Pacific Northwest. The upper level ridge axis
has shifted east of the Cascades this morning, allowing some broken
high clouds to stream into the area in southwest flow aloft ahead of
the next system set to impact the region this weekend. Temperatures
are mostly running in the 30s in the interior valleys as of 3 AM
Friday, with the exception of eastern parts of the Portland metro
where lingering breezy conditions through the Gorge have kept
temperatures in the upper 40s. Patchy fog is once again confined
mainly to the southern Willamette Valley, but is less extensive in
coverage and generally less dense than the past few nights. Expect
another mild and dry day across the area, with afternoon highs
around 60 degrees and partly sunny skies as high clouds continue to
stream into the area ahead of the impending system looming offshore.
Temperatures will run a few degrees warmer across the area tonight
into Saturday morning as the ridge breaks down and cloud cover
continues to increase, with some patchy fog development remaining
possible in the interior valleys.

Guidance continues to trend slower with the onset of precipitation
across the area on Saturday as the shortwave trough and associated
surface front remain offshore tonight and don`t push inland until
Saturday afternoon. A such, do not expect rain to develop in coastal
areas until Saturday morning. The fastest guidance now depicts rain
spreading inland to the Willamette Valley  late Saturday morning,
with the slowest solutions holding rain off until late afternoon or
early evening. QPF amounts are roughly in line with previous
forecast packages, showing 0.25-0.75" along the coast and only 0.10-
0.25" inland through Sunday morning. Showery conditions will then
linger through the day on Sunday between systems, with temperatures
remaining close to seasonal norms in the upper 50s.

A more potent frontal system will cross the area late Sunday into
Monday, bringing a more widespread soaking rain to the region along
with increased thunderstorm chances as instability and upper level
forcing increase. ECMWF`s Extreme Forecast Index has backed off
somewhat in signaling a higher end rainfall event with respect to
climatological norms, but robust rainfall amounts are nonetheless
expected across the area through Monday evening. This is reflected
in NBM guidance which depicts 25th-75th percentile interquartile
ranges for 24 hr QPF of 1.00-2.50" on the coast and 0.50-1.50"
inland through Monday. Another system will follow Tuesday night into
Wednesday with an additional 1-2 inches of rain for coastal areas
and perhaps another 0.75-1.25" inland. Given the amount of rain in
the forecast, we will likely see significant responses on area
rivers during the first half of next week, in addition to ponding of
water and potential for clogged storm drains. Latest HEFS guidance
is on track with previous thinking, showing around a 10-15 percent
chance for some of the rivers draining the Coast Range to reach
flood stage next Tuesday/Wednesday. Probabilities remain lower at
this time for inland rivers. Will certainly need to keep a close eye
on hydro concerns moving forward into next week.

Meanwhile, snow will return to the High Cascades as snow levels fall
to around 4000 feet on Monday, with NBM guidance showing around a 60
percent chance to surpass a foot of snow in the passes for the 48 hr
period ending early Wednesday morning. /CB

&&

.AVIATION...Southwest flow aloft with increasing mid to high level
clouds. Predominately VFR conditions expected through the TAF
period. Winds generally remain light and offshore, except in the
vicinity of the Columbia River Gorge where winds will continue to
gust to around 20-25 kt through 20z. A front is expected to approach
the coast late tonight into Saturday morning and will bring
increasing chances for rain through Saturday.

PDX APPROACHES...VFR with variable high clouds. Light southeast
winds, up to 5 kt in the afternoon. -Batz/DH


&&

.MARINE...Light offshore winds turn southerly today ahead of a slow
moving front. Winds increase by Saturday morning with gusts up to 20-
25 kt. A stronger frontal system is expected to arrive on Sunday
with Gales likely across the coastal waters Sunday night. Will
maintain breezy westerly winds through Monday as the parent low
moves toward Haida Gwaii.

A northwest swell will maintain seas of at least 7 to 9 ft with a
period of around 13 to 15 seconds today, and through the weekend.
Seas will likely climb to around 10 ft on Saturday. Still expecting
a robust westerly swell to build seas into the upper teens Monday
night into Tuesday morning, with around a 45-65% chance of seas
exceeding 20 ft.

Active weather is expected to continue with the potential of another
strong, gale force frontal system Tuesday into Wednesday. Latest
guidance also suggests there is a 30-50% chance of maximum wind
gusts exceeding 48 kt with this system, so will need to monitor the
possibility of Storm Force winds for next week. /DH

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...None.
WA...None.
PZ...None.

&&

$$

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