320
FXUS66 KMFR 172107
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
207 PM PDT Fri Jul 17 2026

.KEY MESSAGES...

*Critical fire weather conditions expected Friday (7/17) afternoon
 and evening for portions of the Shasta Valley, eastern Siskiyou,
 Modoc, southeast Klamath and southwest Lake Counties.

* Hot, dry, breezy, unstable conditions will continue each day
 through the weekend.

*Smoke will persist for Jackson and Klamath Counties through the
 weekend.

*Thunderstorms re-enter the forecast beginning as early as Monday,
 mainly for the Cascades and east. Lesser chances beginning
 Tuesday for areas west of the Cascades.

&&

.DISCUSSION...Satellite imagery shows mainly cloud free skies
across southern Oregon and northern California. However, the
satellites are picking up on infiltrating the Rouge Valley from
the East Evans Creek Fire. This smoke is creating significant air
quality concerns and the Oregon Department of Environmental
Quality has issued an Air Quality Advisory for Jackson, Klamath,
and northern Lake Counties through at least noon Monday. The HRRR
smoke model continues to show smoke impacts through the weekend.
While the smoke is not great in general, it does come with a
couple of benefits. Afternoon high temperatures may be a little
lower than forecast, and winds and instability will dampen
somewhat in the areas of heavy smoke.

A warming and drying trend will begin this weekend as a low
pressure system moving into Canada will continue to move away from
southern Oregon and northern California. This will bring in
general deep southwest flow as the 4 corners ridge builds in
again. With the warming and drying trend, winds will also trend
weaker this weekend.

Then on Monday, confidence in the forecast decreases as another
low looks to dig in off the west coast and be juxtaposed with the
4 corners high. Depending on the location and timing of these
larger scale features a few different scenarios could happen.
Should the ridge build farther west, we could look for much warmer
temperatures through the week bringing hot, dry, breezy and
unstable conditions to the area. Should the high push farther east
with the low closer to us, this could tap into some deep moisture
bringing thunderstorms chances to areas along and east of the
Cascades beginning as early as Monday (but more realistically
Tuesday and Wednesday). These storms could even push west of the
Cascades on Tuesday and Wednesday, but ensembles do not
necessarily favor this solution as the NBM continues to to favor a
5-15% chance for storms.



&&

.AVIATION...17/18Z TAFs...VFR skies will prevail across most of
the area through the TAF period. The exceptions to this will be
areas of heavier smoke, particularly for Jackson County and the
Rogue Valley International Airport where visibilities have
reduced to MVFR. Klamath County could also see some heavier smoke
linger bringing down visibilities at times across Kingsley Field
among other airports.


The only other exception will be marine stratus along portions of
the coast and offshore as part of the coastally trapped wind-
reversal. While the stratus has dissipated and skies will remain
clear through the afternoon. Expect IFR ceilings and visibilities
to return in the late evening and overnight across the entirety of
the coast.


&&

.MARINE...Updated 200 PM PDT Friday, July 17, 2026...Increasing
north winds will build steep seas south of Cape Blanco this
afternoon, with steep seas spreading to all waters on Saturday.
As north winds peak late Saturday and Sunday, areas of very steep
seas may develop south of Port Orford. Conditions gradually improve
on Monday, but steep seas may linger with the dominant wind waves
transitioning to fresh swell. Improved conditions are likely on
Tuesday. A low pressure may move up from the south late  Tuesday and
Wednesday. This low may remain well offshore and weaken as it moves
north. It will bring chances for 3-6 ft southerly swell and chances
for showers.


&&

.FIRE WEATHER...Updated 200 AM PDT Friday, July 17, 2026...
The two main aspects of the forecast for particular analysis this
afternoon were the extent of hot, dry, and breezy/windy
conditions today through Sunday, and the potential risk and
coverage of thunderstorms while inland temperatures remain above
normal during Monday through Wednesday.

A Red Flag Warning continues this afternoon and evening,
remaining in effect for southwest Lake and southeast Klamath
counties, and zone 285 in Modoc County and much of central and
eastern Siskiyou County (Zones 281 and 284). The strongest south
winds of this event are expected to occur for the eastern portion
of the Shasta Valley. A slow moving dry front will winds to a
peak of strength in the late afternoon.

The forecast through the weekend is consistent and pretty straight-
forward. Temperatures will trend upward, humidities will remain
drier than normal, and afternoon winds will trend back to typical
strength for Sunday. That being said, areas of heavy smoke from
the East Evans Creek fire may dampen some of the winds and
instability.

Hot, dry, and breezy conditions are expected Saturday and Sunday.
Temperatures of 5 to 10 degrees above normal are expected through
the weekend. Afternoon wind speeds will trend back to typical values
by Sunday. Minimum afternoon humidities will remain very low on
Saturday then trend slightly upward on Sunday. The slight moistening
of the air mass on Sunday will be accompanied by a late day increase
of high clouds, and perhaps some east side cumulus buildups. The
majority of ensemble solutions favor the hotter, drier ECMWF. But,
there is about a 20% probability of a slightly less hot, but
noticeably more moist air mass as depicted by the operational GFS
run.

In that case, instability could develop as early as late Sunday
night into Monday morning, with a few very light showers or virga
possible over the higher terrain. A risk of thunderstorms could
develop as early as Monday afternoon, with a higher probability of
thunderstorms, highest for Lake and Modoc counties, on Tuesday and
Wednesday afternoons. Though not as indicated by the GFS, a more
expansive analysis shows chances for Monday thunderstorms remain
very slight (5-10%) and predominantly over the east side. On
Tuesday, 10-15% chances cover most of the east side, with a lesser
5% to 10% probability extending into Jackson, Siskiyou, and eastern
Douglas counties. Particularly if the GFS were to verify, for areas
where thunderstorms do not develop, the potential instability added
to continuing hot and dry conditions could lead to elevated critical
condition concerns and enhanced behavior on existing fires.

Model uncertainty still increases further beginning Wednesday with
differences in whether an unstable air mass will linger or shift
east of our area. Late in the week (Thursday/Friday), some eastward
movement in the pattern is likely, which is likely to shift the
region of instability east of our area. But, with a plausibly slower
solution keeping instability over eastern portions of Lake and Modoc
counties.


&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Red Flag Warning until 8 PM PDT this evening for ORZ624.

CA...Red Flag Warning until 8 PM PDT this evening for CAZ281-284-285.

PACIFIC COASTAL WATERS...Small Craft Advisory from 11 AM to 11 PM PDT
     Saturday for PZZ350-356-370-376.

&&

$$