659
FXUS66 KMFR 082335
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
335 PM PST Mon Dec 8 2025

.Updated Aviation Discussion.

.DISCUSSION...A strong upper ridge off the California coast this
week will keep much of the moisture associated with a strong
atmospheric river to our north. The frontal boundary associated
with that moist plume will settle southward later tonight into
Tuesday and this will bring increasing rain chances to NW sections
of our forecast area and also the coast/coast ranges, but the
impactful rainfall will largely stay to our north. In fact, many
areas south of the Umpqua Divide and east of the Cascades won`t
see any rainfall from this system at all. As the front edges
southward tonight through Tuesday evening, mid level winds will
increase in NE portions of our area and this will bring
occasionally gusty winds from the Cascades eastward in Oregon
(primarily north of Highway 140). Limited vertical mixing could
make it difficult for the winds to completely mix down to the
surface, so the strongest winds will be over the higher terrain,
but also possibly in some of the more typically channeled valleys
(around Summer Lake). Please refer to our wind advisory for the
details.

After the front briefly jogs southward, the upper ridge will re-
strengthen at midweek and amplify as it heads into California and
the West Coast late this week into the weekend. As such, moisture
will shift well to our north and precip chances will diminish
Wednesday to almost nil everywhere Thu-Sat. Overall, we`re
expecting yet another dry, mild period for this time of year,
which isn`t exactly a good thing since we`re heading into
(climatologically) our wettest time of the year and snowpack is
pretty much non-existent. This pattern will probably bring more
valley/basin low clouds/fog during the nights/mornings. Areas that
remain clear will have cold mornings, but also milder afternoons.
It`s not out of the question that some of the climate sites in
NorCal (Montague, Mount Shasta, Alturas) and perhaps even Klamath
Falls challenge a mid-December record high or two late this week.

Beyond that, models show the upper ridge axis pushing east of the
Cascades Saturday night with a Pacific frontal system approaching
the coast and moving inland Sunday. Most ensemble members weaken
this front as it moves onshore, so it remains to be seen just how
much, if any precipitation it will bring. Will this be the system
that opens the storm door for our area? While the CPC 8-14 day
forecast gives hope for a wetter period next week (odds are shown
to be 50-60% for above normal precip), model clusters and
ensembles still show plenty of drier solutions within the
membership and a tendency for upper ridging near or just off the
California coast. If that ridge remains strong enough, this could
keep the storm track to our north. -Spilde


&&

.AVIATION...09/00Z TAFs...Along the coast and just offshore, IFR and
LIFR ceilings are expected to be the predominate condition through
the TAF period, with visibility also lowering Tuesday morning as the
front slowly sags south.

Inland, VFR is likely into this evening. Then expect, lower ceilings
to develop again tonight into Tuesday morning, down to MVFR, then
IFR/LIFR. Areas of fog and terrain obscuration is also likely west
of the Cascades. Strong winds aloft develop near the Cascades and
over the east side in Oregon (north of Highway 140) tonight into
Tuesday where higher terrain could experience gusts in excess of 50
mph. This could lead to some low-level wind shear over there (NE of
Klamath Falls) since a low-level inversion probably doesn`t allow
these winds to mix all the way to the surface in some valleys. Even
so, vertical mixing may improve Tuesday to allow surface wind gusts
to 50 mph from around Summer Lake eastward. -Spilde/Petrucelli


&&

.MARINE...Updated 200 PM PST Monday, December 8, 2025...Gusty
south winds and steep wind waves combined with westerly swell will
bring hazardous conditions to small craft tonight through at least
Tuesday. Winds subside, but west swell persists into Wednesday,
especially across the north. Conditions improve around mid-week
as swell dominated seas gradually lower. Expecting light rain
over the waters through mid-week which could reduce visibilities
at times (fog/low clouds expected as well) over the next couple
days. -Spilde/JWG


&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Wind Advisory from 7 PM this evening to 10 PM PST Tuesday for
     ORZ030-031.

CA...None.

PACIFIC COASTAL WATERS...Small Craft Advisory until 1 AM PST
     Wednesday for PZZ356-376.

     Small Craft Advisory until 10 AM PST Wednesday for PZZ350-370.

&&

$$

MAS/JWG