497
FXUS66 KMFR 220016
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
516 PM PDT Fri Aug 21 2026

...Updated the Aviation and Marine Sections...

.AVIATION...22/00Z TAFs...Marine stratus will persist tonight
through Saturday night with mainly IFR along the coast and over the
marine waters. Patches of LIFR will be at maximum coverage late
tonight into early Saturday morning. Also, drizzle is possible along
and west of the coastal ranges.

Inland, VFR conditions will prevail. High clouds from the Cascades
eastward will gradually shift north-northeastward, out of the area
by late Saturday morning. Gusty winds will linger early this
evening, and return for Saturday afternoon and evening. The
strongest winds will be east of the Cascades and in the Shasta
Valley, with south to west gusts today and southwest to northwest
gusts on Saturday at 20 to 40 kt. Winds will ease after sunset.

&&

.MARINE...Updated 830 PM PDT Friday, August 21, 2026...Light winds
and low seas will persist into Sunday morning. Southerly winds will
shift to westerly Saturday as a weak front dissipates over the
waters. A thermal trough will develop Sunday with increasing
northerly winds. These winds will likely be hazardous to small
craft south of Cape Blanco late Sunday morning through Monday
morning. The area of stronger winds is likely to shift offshore,
beyond the inner waters, during Monday. Winds are then likely to
diminish again later Monday night through Tuesday into Wednesday.

&&

.PREV DISCUSSION... /Issued 252 PM PDT Fri Aug 21 2026/

KEY MESSAGES...

* While marine stratus persists over coastal areas and clouds
  stream to the north inland, activity is unlikely this afternoon
  and evening.

* A Red Flag Warning is in place for the Shasta Valley as well as
  Klamath and eastern Lake counties this afternoon and evening for
  gusty winds and low relative humidities (RHs). For Saturday
  afternoon and evening, a Red Flag Warning is in place across
  Klamath and Lake counties.

* Winds ease on Sunday, with a generally unimpactful pattern
  expected for next week.

DISCUSSION...A cutoff low passing to the west will guide area
weather today and through much of the weekend. While marine stratus
lingers along the Oregon coast and clouds are streaming from south to
north over more inland areas, activity is not expected today
(although virga may bring some hopes up). Radar returns show a line
of higher returns over the Cascades and moving eastward, so a few
stray showers are possible into parts of Klamath County. But with
cloud cover limiting daytime heating, convective instability will be
limited. Thunderstorms aren`t entirely out of the question, but
chances have trended downward for this afternoon and evening (5-
10%). With gusty winds and dry surface air being observed, a Red
Flag Warning is in place for the Shasta Valley as well as across
Klamath and eastern Lake counties.

The low stats to swing inland over Washington state on Saturday.
With drier air aloft, precipitation is not expected. Gusty southerly
winds will move eastward, which will take the Shasta Valley out and
put the rest of Lake County in a Red Flag Warning for Saturday
afternoon and evening. Areas under marine stratus will see cooler
temperatures while inland areas will be at seasonable temperatures.

The cutoff low is expected to be to the northeast by Sunday,
bringing a southwest flow pattern that will generally persist
through the week ahead. A shortwave ridge is currently expected to
bring temperatures 5-10 degrees above normal for Monday and Tuesday.
An upper trough passing to the north will bring temperatures back
down on Wednesday and Thursday, with elevated westerly winds over
Lake and Modoc county terrain possible depending on its position.
Deterministic models start to diverge into Friday and beyond, but
meteograms show agreement that the rest of August looks to stay
dry. -TAD

FIRE WEATHER...Updated 130 PM PDT Friday, August 21, 2026...An
upper level trough will pass through the region today into Saturday,
bringing a period of increased winds and critical fire weather
conditions. Afternoon winds increase today as the trough and
associated dry cold front approach the region (gusts 25-35 mph), but
daytime humidities will also trend somewhat higher compared to
yesterday. Despite the uptick in humidities, it`s close enough with
the higher confidence on more widespread higher winds on Friday to
warrant maintaining a Red Flag Warning for FWZs 281, 284, 285 and
624. Sustained winds won`t quite reach criteria for FWZ 625 today,
but by Saturday, however, 700 mb winds will peak in strength east of
the Cascades and more widespread sustained winds of 15 to 20 mph are
expected as the dry front passes. Additionally, daytime RHs will
trend lower again, so another day of critical fire weather
conditions is expected on Saturday. The Fire Weather Watch has been
upgraded to a Red Flag Warning for FWZs 284/285/624/625 for gusty
winds and low RH for Saturday afternoon/evening.

In addition to wind/RH concerns for today and Saturday, there is the
potential for isolated showers and very isolated thunderstorms
today. Ample cloud cover so far is expected to limit daytime heating
and instability, which should keep the lightning potential minimal
today. There are some returns on radar this afternoon, but very
little, if any, precipitation is making it to the ground. By
Saturday, the mid-levels dry out and thunderstorm threat will shift
well north of the forecast area into northern Oregon/Washington.

More typical summer conditions return Sunday and persist into early
next week. There are some signals for thunderstorm chances across
eastern 285/625 on Monday, but much will depend on how far west the
Four Corners High retrogrades behind this trough passage. Otherwise,
another trough drops southward from the Gulf of Alaska and lingers
off the BC coast through early next week. There will likely be
additional shortwaves/troughs to swing through the region early next
week, bringing periods of enhanced winds. Stay tuned for updates.
/BR-y

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Red Flag Warning until 9 PM PDT this evening for ORZ624-625.

CA...Red Flag Warning until 9 PM PDT this evening for CAZ281-284-285.

PACIFIC COASTAL WATERS...None.

&&

$$