486
FXUS66 KMFR 291130
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
430 AM PDT Fri Aug 29 2025


.UPDATE...Updated Aviation Discussion.


&&

.AVIATION...28/12Z TAFs...Along the coast, MVFR/IFR conditions with
local LIFR will continue through this morning.  Some localized
improvement to MVFR is expected late this morning or early in the
afternoon, but most locations will not clear fully before IFR/LIFR
develops Friday evening.

Elsewhere, VFR conditions will prevail through the next 24 hours,
with the exception of some localized lower flight visibilities in
smoke in the vicinity of or downwind from area wildfires.


&&

.PREV DISCUSSION... /Issued 307 AM PDT Fri Aug 29 2025/

DISCUSSION...Warm and dry conditions are expected through the
weekend as and upper low remains well offshore, gradually shifting
northward late Sunday. Meanwhile, an upper level ridge will remain
over inland areas, centered to the east of the area.  Southwest
Oregon and northern California will be under a southwest flow
pattern through Sunday with some very weak instability and mid
level moisture present, mainly for areas from the Cascades east.
High resolution models support a low chance (10%) for some
isolated showers or thunderstorms, mainly east of the Cascades,
this afternoon and evening. Mainly, expect cumulus clouds to
develop but cannot rule out an isolated shower or thunderstorm for
these areas. This pattern continues into the weekend, but is
slightly weaker and ensembles indicate a low potential for
thunderstorms (5-10%) Saturday and Sunday.

Across inland areas, breezy to gusty afternoon/evening winds are
expected through the weekend. This combined with dry humidities
will bring some elevated fire weather concerns each afternoon
through Sunday, especially for areas in northern California and
east of the Cascades. Additionally, periods of wildfire smoke and
haze will continue to affect southwest Oregon and northern
California at times.

Along the coast, weak onshore flow is resulting in a marine push
with widespread low clouds overnight, and expected to persist
through the morning. These low clouds may spread into portions of
the central Umpqua early in the morning. Low clouds will gradually
retreat to the coast with partial clearing along the coast during
the afternoon. Then, expect a return of low clouds and fog along
the coast Friday night and Saturday morning. Areas of low clouds
and fog are expected again Saturday night and Sunday night, but
these conditions may not be as widespread.

The pattern begins to change late Sunday into early next week as
the upper level low gradually shifts northward and the upper
ridge strengthens across the region. This will result in
temperatures trending hotter Monday through Wednesday.
Additionally, ensembles indicate the potential for an upper level
shortwave to move into the area from the south on Tuesday, which
may bring sufficient mid-level moisture and instability to bring
a potential for thunderstorms. Currently, the National Blend of
Models supports a 10% chance for thunderstorms on Tuesday.
However, some ensembles members indicate higher potential for
thunderstorms, mainly from the Cascades east. So, we will monitor
this potential closely and update as confidence increases in the
details.

 &&

AVIATION...28/06Z TAFs...Along the coast and just offshore, IFR and
MVFR conditions this evening will transition to LIFR/IFR as as the
marine stratus deck lowers. Some localized improvement to MVFR is
expected late Friday morning or early in the afternoon, but most
locations will not clear fully before this same process repeats
Friday evening.

Elsewhere, VFR conditions will prevail through the next 24 hours,
with the exception of some localized lower flight visibilities in
smoke in the vicinity of or downwind from area wildfires. -BPN

MARINE...Updated 200 AM PDT Friday, August 28, 2025...Relatively
light south winds and low seas will persist through Saturday.
Winds turn northerly Sunday and increase as a weak thermal trough
develops. Breezy to gusty north winds return Sunday afternoon into
Monday, especially south of Cape Blanco, with steep seas possible
by Tuesday. These conditions are likely to persist through at
least mid-week.

FIRE WEATHER...Updated 200 AM PDT Friday, August 29, 2025...An
upper low will remain positioned off the Oregon coast, with
southwest flow across the area today into the weekend. Models
indicate marginal instability and weak mid level moisture over
portions of the area this afternoon and evening, with a low chance
(10%) for some isolated showers or thunderstorms, mainly from the
Cascades east. This pattern continues into the weekend, but is
slightly weaker, with a very low (5-10%) chance for isolated
convective showers or thunderstorms in the afternoon/evening from
the Cascades east. The most likely scenario will be building
cumulus in the afternoons, then dissipating around sunset.

Breezy to gusty winds and dry humidities are expected through
Saturday across inland valleys. While relative humidity will be
low, especially east of the Cascades and across northern
California zones, winds are not expected to be high enough for
critical conditions to be met. However, some locally, brief near
critical to 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.

There`s good agreement the upper low will move little and actually
drift north off the Washington coast Sunday into Monday as an
upper ridge gradually strengthens over the region. Temperatures
are expected to remain above normal Sunday. We`ll still have to
deal with breezy afternoon and early evening winds and low
relative humidity for the same areas mentioned above, with brief
periods of near or critical conditions possible. While we may
approach headline thresholds, we do not expect to reach critical
conditions at this time.

Temperatures will trend hotter next week as the upper level high
pressure ridge strengthens over the region. Additionally,
thunderstorm potential may increase early next week as some models
shows an upper level disturbance moving from south to north
across the area. Mid level moisture and weak instability may be
sufficient by Tuesday to bring some isolated thunderstorms,
mainly east of the Cascades. However, confidence is low in the
details for thunderstorms at this time. We will continue to
monitor this concern.

PREV LONG TERM DISCUSSION... /Issued 808 PM PDT Thu Aug 28 2025/

The pattern continues to transition early next week with the
upper level ridge amplifying over the intermountain west as energy
dives southward into the mid-west. As this ridge amplifies, low
pressure offshore 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. Upper 90s for the West Side (upper 80s for East
Side) is likely (80- 90%) for this warm up, with a 70-80% chance
of triple digits in West Side Valleys for the middle of next week.
At this time, the warm looks to be shortlived, with the pattern
transitioning again toward the end of next week and a possible
cool down for the following weekend.

With a general southwest to southerly flow over the region through
much of the forecast period, the bulk of the smoke impacts from the
Emigrant fire should remain north of the forecast area. Latest HRRR
Smoke model does indicate the potential for higher smoke
concentrations in the northern portions of Klamath County as late
evening northerly winds could bring smoke from the Emigrant fire
farther south. If this happens, models also show improvement in the
afternoon as the typical diurnal winds increase and clear out the
air. Meanwhile, smoke impacts from the Dillon fire in western
Siskiyou County should remain confined to western Siskiyou County.
Models show higher smoke concentrations settling in the
Scott/Shasta/Klamath River Valleys at night, then clearing out with
the increase in afternoon winds as well.

Stay tuned for updates as details become more clear over the coming
days. /BR-y

&&

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

CA...None.

PACIFIC COASTAL WATERS...None.

&&

$$