333
FXUS66 KMFR 210007
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
507 PM PDT Thu Aug 20 2026

.KEY MESSAGES...

* Daytime highs today will be 5 to 10 degrees above normal today.

* A passing cutoff low will bring cooler temperatures across the
  area on Friday and over the weekend.

* Slight thunderstorm chances along the Cascades and into northern
  Klamath County are in the forecast for Friday afternoon and
  evening. Fire weather concerns are present in the Shasta Valley
  and east of the Cascades in the afternoons and evenings as
  well.

* Seasonal weather is expected next week.

&&

.DISCUSSION...With an upper level ridge over the southern
United States nudging over the area, another day of above average
temperatures is expected for inland areas of northern California and
southern Oregon. The Umpqua Valley looks to be in the mid 90s, while
other west side valleys are forecast to be in the high 90s to the
low 100s. Farther east, area valleys and basins will be in the high
80s to low 90s. With a cutoff low approaching, southerly flow
funneling into the Shasta Valley will bring elevated winds this
afternoon and evening. A Red Flag Warning has been issued for the
Shasta Valley for the combination of these winds and ongoing dry
condition creating an environment where fires can quickly spread.

That cutoff low will pass to the west over the Pacific Ocean, but
will push ridging to the east and bring lower temperatures across
the area on Friday and through the weekend. Widespread precipitation
is not expected, but some coastal areas may see light mist under
marine stratus. Friday afternoon and evening will also have a slight
chance (5-15%) for thunderstorms along and east of the Cascades.
Increased moisture aloft is supporting these chances. However, weak
instability and expected cloud cover reducing surface heating are
keeping those chances low. Also on Friday after noon and evening,
gusty winds develop into the Shasta Valley and across areas east of
the Cascades. A Red Flag Warning is in place for these areas on
Saturday afternoon and evening for the combination of gusty winds
and low humidities. Winds ease in the Shasta Valley on Saturday,
reducing fire weather concerns. East of the Cascades, a Fire Weather
Watch is in place to address continuing concerns from elevated
winds. Winds ease further on Sunday.

By early next week, the cutoff low will be off to the northeast.
With southwest flow between an upper trough to the northwest and
ridging persisting to the southeast of the area, next week is
looking fairly uneventful. Current imagery shows the trough keeping
the ridge at bay, which will bring average temperatures. Minor
disturbances in the upper flow  may bring breezy afternoons, but the
timing remains unclear. Long term meteograms show little hope for
precipitation through the rest of August. -TAD


&&

.AVIATION...21/00Z TAFs...Marine stratus will persist through much
of the TAF period along the coast and over the marine waters with
LIFR/IFR conditions this evening through Friday morning, lifting to
MVFR by Friday afternoon.

Inland, VFR conditions will prevail with high clouds overhead.
However, there is a low chance (20%) for MVFR to spread into the
Umpqua early Friday morning, including at Roseburg.  Otherwise,
expect some enhanced breezes this evening, with gusty winds expected
in the Shasta and Scott Valleys. Winds will ease after sunset, but
mid and high level clouds will persist overnight into Friday as an
upper level trough approaches the region. Gusty winds will develop
Friday afternoon, strongest east of the Cascades and in the Shasta
Valley.


&&

.MARINE...Updated 230 PM PDT Thursday, August 20, 2026...Below
advisory seas continue through Saturday for area waters. A thermal
trough pattern will bring gusty northerly winds to all waters on
Sunday afternoon. Steep seas are expected south of Cape Blanco by
the evening, with localized areas of very steep seas showing up
south of Brookings in current guidance. Steep seas may reach as far
north as Reedsport. The trough will not last long, with winds and
seas easing by Monday afternoon. Below advisory seas are forecast
through midweek, with a thermal trough possibly returning towards
the end of next week. -TAD

&&

.FIRE WEATHER...Updated 200 PM PDT Thursday, August 20, 2026...The
upper level pattern is transitioning today as a trough offshore
moves closer to the PacNW. This will start a period of increased
winds that will persist through Saturday as this low pressure
gradually moves inland into the PacNW through the weekend.

Hot temperatures will peak today and RHs will trend lower a bit.
We`ll see an increase in afternoon winds today, but for most areas,
winds won`t quite be strong enough (widespread gusts of 15-20 mph)
to reach critical fire weather thresholds. The exception will be in
the Shasta Valley where southerly flow will enhance winds the most
in that area. This combined with RHs in the low to mid teens should
bring a long enough period of critical conditions today, so we`ve
gone ahead with a Red Flag Warning for Fire Weather Zone (FWZ 281)
for this afternoon/evening. Isolated critical conditions are
possible for areas east of the Cascades today, but the more
widespread critical conditions are expected Friday and Saturday.

Afternoon winds increase Friday (gusts 25-35 mph), but daytime
humidities will also trend somewhat higher compared to today.
Despite the uptick in humidities, it`s close enough with the higher
confidence on more widespread higher winds on Friday to warrant
upgrading the Fire Weather Watch to a Red Flag Warning for FWZs 281,
284, 285 and 624. Decided to keep FWZ 625 out for Friday as
confidence is not high enough for sustained winds to reach criteria
on Friday. By Saturday, however, 700 mb winds peak in strength east
of the Cascades and more widespread sustained winds of 15 to 20 mph
are expected. Additionally, daytime RHs will trend lower again, so
another day of critical fire weather conditions is possible on
Saturday. A Fire Weather Watch is also in effect for FWZs
284/285/624/625 for gusty winds and low RH.

In addition to wind/RH concerns for Friday and Saturday, mid-level
moisture increases today and Friday, raising the concern for
thunderstorm potential. Overall, the thunderstorm threat looks
minimal for our area. Widespread cloud cover on Friday will likely
inhibit daytime instability, and by the time any decent forcing
arrives to tap into what little elevated instability there is, the
mid-levels are beginning to dry out. So it`s not impossible for
isolated activity, but it`s only a low chance (10-15%) at this time,
primarily along the Cascades from Crater Lake northward and across
northern Klamath/Lake Counties. With the approach of the trough
tonight into Friday, we`ve been monitoring the potential for any
nocturnal convection, but current guidance is lacking the necessary
parameters for this. Even still, can`t completely rule it out, but
would only give it about a 5% chance of occurring and primarily for
western Siskiyou County. Drier air in the mid-levels is well
established for our region by Saturday, which shifts any
thunderstorm threat northward into northern Oregon for Saturday.

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 from 2 PM to 9 PM PDT Friday for ORZ624.

     Fire Weather Watch from Saturday afternoon through Saturday
     evening for ORZ624-625.

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

     Fire Weather Watch from Saturday afternoon through Saturday
     evening for CAZ284-285.

PACIFIC COASTAL WATERS...None.

&&

$$