316
FXUS66 KMFR 240534
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
1034 PM PDT Sun Aug 23 2026

.KEY MESSAGES...

* Temperatures peak about 5 to 10 degrees above normal on Monday
  before returning to seasonal levels near midweek.

* There will be a slight chance (20 percent) of thunderstorms
  across southeastern Lake County and Modoc County Monday
  afternoon.

* A passing shortwave will bring elevated fire weather conditions
  (gusty winds and low humidities) to areas west of the Cascades
  on Monday. A red flag warning is in effect for the southern
  Oregon Cascades and westward into Jackson County, the Siskiyou
  Mountains and western/central Siskiyou County.


&&

.DISCUSSION...The upper trough that has been guiding conditions over
the weekend has moved on to the northeast, leaving southwest flow
aloft under the western side of a continental ridge. This pattern
will bring some warming to most areas today, with easternmost Lake
and Modoc County seeing similar temperatures as on Saturday.

Monday will be the warmest day of the forecast period for most
areas. Temperatures west of the Cascades may reach up to 10 degrees
above normal, while to the east highs look to be about 5 degrees
above normal. A passing shortwave will bring elevated winds into the
Shasta Valley, the Klamath Basin, Christmas Valley, and parts of the
Rogue Valley. For western Siskiyou County, Jackson County, and
western Cascades foothills, these winds align with ongoing dry
conditions to possibly reach critical fire weather conditions. A Red
Flag Warning has been issued for Monday afternoon and evening to
highlight these concerns. This shortwave is also support slight (15-
20%) thunderstorm chances over eastern Modoc and Lake counties,
given its interactions with monsoonal moisture moving over those
areas. While the chances for thunderstorms are not high enough to
meet Red Flag criteria, any thunderstorms that do develop can still
be locally hazardous by bringing lightning strikes or erratic and
gusty winds.

On Tuesday, an approaching trough around a low pressure system over
the Pacific will shift flow to be more southerly. With dry air aloft
precipitation is not expected. Temperatures west of the Cascades
will drop a bit, but highs across the area look to stay about 5
degrees above normal. A weak front swinging around that trough may
bring marine drizzle and some inland cloud cover On Tuesday morning,
but significant impacts are not expected.

For midweek and into the weekend, the upper trough starts to work
against high pressure centered around the Four Corners area. The
first low will weaken and move off to the northeast but another low
follows to keep the trough in place possibly through Saturday. With
this pattern, slow and steady cooling would bring generally
seasonable warmth across the area by Friday or Saturday. Upper
disturbances may bring elevated breezes on Friday, but details that
far out are hard to forecast with high confidence. Overall, the
forecast through the rest of August looks to be unimpactful. -TAD


&&

.AVIATION (06Z TAFs)...

Marine stratus with IFR/LIFR will redevelop along the coast
overnight and persist through late Monday morning.  Otherwise, VFR
conditions are expected for inland TAF sites. Gusty winds will
develop for inland areas late Monday afternoon and evening.
Additionally this is a slight chance (20%) for thunderstorms across
Modoc and southeastern Lake county Monday afternoon and early Monday
evening. Gusty outflow winds may accompany storms on Monday.

&&

.MARINE...Updated 230 PM PDT Sunday, August 23, 2026...Gusty north
winds and steep wind-driven seas are building steep seas across
area waters this afternoon. These winds will persist through Monday
morning. The main belt of stronger winds will push into the outer
waters Monday afternoon and evening, with a southerly surge of wind
and fog along the inner waters Monday night into Tuesday. Generally
light winds and calm seas are then expected through Friday with low
pressure persisting over the northeastern Pacific.

&&

.FIRE WEATHER...Updated 230 PM PDT Sunday, August 22, 2026...
With ongoing dry conditions, a passing shortwave will bring elevated
winds to areas west of the Cascades. These winds will be southerly
in the Shasta and could approach 30 to 35 mph. The Scott Valley
could also see southerly winds approach 20 to 25 mph. In the eastern
Rogue Valley, westerly winds could reach 20 to 25 mph. With RHs
forecast to be in the 10-15% range, this combination represents
critical fire weather conditions as any new fires could quickly
spread. A Red Flag Warning for gusty winds and low RHs has been
issued for California fire weather ones 280 and 281 as well as
Oregon fire weather zones 621, 622, and 623. This Warning will be in
place from 11 AM through 8 PM on Monday.

Also on Monday, There are some signals for thunderstorm chances
across far eastern 285/625, namely the Warner and Hart mountains.
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.


&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Red Flag Warning from 11 AM to 8 PM PDT Monday for ORZ621>623.

CA...Red Flag Warning from 11 AM to 8 PM PDT Monday for CAZ280-281.

PACIFIC COASTAL WATERS...Small Craft Advisory until 11 AM PDT Monday
     for PZZ350-356.

     Small Craft Advisory until 8 PM PDT Monday for PZZ370-376.

&&

$$