830
FXUS66 KMFR 301757
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
1057 AM PDT Sat Aug 30 2025

.Updated Aviation Discussion.

.AVIATION...30/18Z TAFs...Satellite imagery shows high clouds moving
onshore over coastal areas of southern Oregon. Ceilings should
remain VFR along the coast and just offshore. Marine stratus is
likely to form early this evening (2-4z) with IFR ceilings that
could last until the end of the TAF period, although ceilings could
improve to MVFR towards 18z tomorrow.

Inland, VFR conditions will last through the TAF period. The
exception will be in eastern Douglas county where smoke will result
in MVFR visibilities until 21-22z at which point it should mix out
and dissipate. Meanwhile smoke from the Emigrant Fire could drift
south into portions of northern Klamath County this evening and
tonight,  but it`s not expected to result in reduction in visibility
at the Klamath Falls airfield. -Petrucelli


&&

.DISCUSSION...A weak front boundary is draped across the marine
waters this morning, associated with a cut off upper level low
that will linger offshore this weekend. This front will continue
to weaken as moves northward and mostly lingers offshore. Radar is
showing some decent returns with this front, but it`s hard to say
if anything is making it to the surface with a lack of
precipitation observations over the waters. While no sites have
recorded precipitation along the coast, did go ahead and bump up
PoPs over the marine waters where this weak front looks strongest.
Aside from some increased cloud cover, and maybe some sprinkles
along the coast north of Cape Blanco, this front will largely go
unnoticed by the rest of the area with conditions today being
quite similar to those of yesterday. The remainder of the forecast
is on track and no other updates are needed. /BR-y

&&

.MARINE...Updated 800 AM PDT Saturday, August 30, 2025...Relatively
light south winds and low seas will persist through Sunday
morning. Winds turn northerly Sunday and increase slightly as a
weak thermal trough develops. Then, gusty north winds develop
Monday into Tuesday, especially south of Cape Blanco, with steep
seas possible. These conditions are likely to persist through at
least mid-week.

&&

.PREV DISCUSSION... /Issued 604 AM PDT Sat Aug 30 2025/

UPDATE...Updated Aviation Discussion.

AVIATION...30/12Z TAFs...Satellite imagery shows high clouds
moving onshore over coastal areas of southern Oregon. Conditions
are mainly VFR along the coast. Although brief, local MVFR/IFR is
possible early this morning. MVFR/IFR is more likely Saturday
evening and night at the coast.

Inland areas will stay at VFR levels through the TAF period. Smoke
from the Emigrant Fire along the Douglas/Lane County border is
expected to move over Klamath County through Saturday. Smoke may
periodically affect visibilities at Klamath Falls on Saturday
morning, but any effects would likely be brief.

PREV DISCUSSION... /Issued 241 AM PDT Sat Aug 30 2025/

DISCUSSION...Satellite imagery shows an upper low located well
off the coast of Oregon near 44N and 132W. This low is forecast
to gradually drift northward later today through Sunday, becoming
positioned off the coast of Washington. Meanwhile an upper level
ridge will be centered just east of the area. This will bring a
southwest flow pattern over the area with warm and dry conditions
and breezy to gusty afternoon winds. Some weak instability and mid
level moisture will allow for cumulus buildups in the afternoons,
mainly over the Cascades and east side. However, chances for any
showers are very low (5% or less).

Temperatures through the weekend will remain above normal with
highs in the 90s across inland valleys west of the Cascades and in
the mid 80s to near 90 for valleys east of the Cascades. Breezy to
gusty afternoon winds are expected across inland valleys,
strongest in the Shasta Valley and east of the Cascades. This
combined with low humidities may bring elevated fire weather
conditions. However, conditions are not expected to reach critical
thresholds.

Smoke from area wildfires will continue to affect the area,
especially across western Siskiyou County and across Klamath and
northern Lake counties.

Monday into Tuesday, temperatures will trend hotter as a high
pressure ridge strengthens over the region. Winds will continue to
be breezy to gusty in the afternoon and early evening on Monday,
then may trend lower on Tuesday. A weak upper level disturbance
will bring a slight chance for thunderstorms beginning Tuesday and
continuing into Wednesday, mainly across western Siskiyou County,
the Cascades and into areas east of the Cascades. For additional
details on the long term period, please see the previous
discussion below.

FIRE WEATHER...Updated 200 AM PDT Saturday, August 30, 2025... An
upper low will remain positioned off the Pacific Northwest coast,
with southwest flow across the area this weekend. Warm and dry
conditions are expected to continue across the area. Models
indicate marginal instability and weak mid level moisture over
eastern portions of the area but with little in the way of an
upper level trigger, mainly expect just building cumulus in the
afternoons, then dissipating around sunset.

Breezy to gusty winds and dry humidities are expected across
inland valleys through the weekend. Overall, winds and humidities
are not expected to reach critical conditions. However, some
locally, brief near critical conditions are possible in the
afternoons, especially in the Shasta Valley and east of the
Cascades. So, we have headlined the gusty winds and dry
humidities.

Models continue to show good agreement that the upper low will
move northward off the Washington coast Sunday into Monday as an
upper ridge gradually strengthens over inland areas. Temperatures
are expected to remain around 5 to 10 degrees above normal on
Sunday, then trend slightly warmer on Monday, and moreso on
Tuesday. Expect continued breezy to gusty afternoon winds and dry
humidities for many inland areas on Monday.

If there`s a window in which thunderstorms could be an issue, it
will be Tuesday and Wednesday afternoon and early evening as weak
upper low drifts north towards our area. Tuesday, the position of
the upper low is such that it could result in at least isolated
thunderstorms for portions of northern California, and Cascades
east.

Wednesday, there`s fairly good agreement the upper low will move
northward into northern California or southern Oregon. The
location of the upper low Wednesday suggest a greater chance for
isolated storms and also covering a larger portion of the area,
and some of the guidance is already showing precipitation (which
is a result of convective feedback). We have added a slight chance
for afternoon and early evening thunderstorms to the areas
mentioned above both Tuesday and Wednesday.

The other question will be the potential for nocturnal storms
Tuesday night and Wednesday night, but much will depend on the
timing and location of the upper low.

It`s also worth noting, the upper ridge will remain in place Tuesday
and Wednesday with afternoon temperatures around the triple digit
mark for the interior westside valleys, and upper 80s to low 90s
east of the Cascades.

PREV LONG TERM DISCUSSION... /Issued 146 PM PDT Fri Aug 29 2025/

DISCUSSION..Tuesday through Thursday will be the time period
worth watching for two reasons: thunderstorm potential and heat.
First, the thunderstorms...Models remain consistent in showing
some energy/weakness in the ridge moving northward through the
region Tuesday through Thursday. In fact, guidance now has a weak
low that takes on a negative tilt as it moves northward, bringing
increasing moisture and instability. We`ve ventured away from the
NBM to add a slight chance of thunderstorms for Tuesday and
Wednesday afternoons/evenings, focused in the typical areas along
and east of the Cascades as well as for portions of western
Siskiyou County. This is still 5-6 days out, so details are likely
to change once this time frame is covered by the models that help
us hone in on timing and location.

Meanwhile, the upper level ridge amplifies over the intermountain
west as energy dives southward into the mid-west. As this ridge
amplifies, the low pressure offshore responsible for the weekend
cooldown, gets pushed northwestward (retrogrades) into the Gulf of
Alaska. We`ll see a warming trend beginning Monday, but models show
the ridge axis being centered over the West Coast States by mid-
week, which is likely result in another warm up across the region
for the Tuesday-Thursday timeframe. Upper 90s for the West Side
(upper 80s for East Side) is nearly certain for this warm up, with a
80-90% chance of triple digits in West Side Valleys for the middle
of next week. While it seems fairly certain that it`ll be hot again
for mid-week next week, with the aforementioned low drifting around
during the same time, cloud cover could end up being a mitigating
factor in the extent of the heat. At this time, the warmth looks to
be shortlived, with the pattern transitioning again toward the end
of next week and a possible cool down for the following weekend.
Regardless, we`ll be evaluating the need for any heat related
headlines over the coming shifts.

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...None.

CA...None.

PACIFIC COASTAL WATERS...None.

&&

$$