903
FXUS66 KMFR 211743
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
1043 AM PDT Fri Aug 21 2026

.Updated AVIATION Discussion...

&&

.AVIATION...21/18Z TAFs...Marine stratus will persist through much
of the TAF period along the coast and over the marine waters with
IFR/MVFR persisting through the afternoon, then lowering again to
LIFR/IFR this evening and tonight. Drizzle is possible along and
west of the coastal ranges.

Inland, VFR conditions will prevail with high clouds overhead. Gusty
winds will develop this afternoon and evening, strongest east of the
Cascades and in the Shasta Valley. Winds will ease after sunset and
high level clouds will gradually move northeast. /BR-y

&&

.PREV DISCUSSION... /Issued 108 AM PDT Fri Aug 21 2026/

KEY MESSAGES...

* Daytime highs today will be about 10 degrees cooler than
  yesterday, then stay around normal for this time of year through
  the weekend.

* Slight thunderstorm chances along the Cascades and into northern
  Klamath County this afternoon and evening.

* Heightened fire weather concerns today and Saturday due to low
  humidity and gusty afternoon/evening winds in the Shasta Valley
  and east of the Cascades.

* Seasonal weather is expected next week.

DISCUSSION...A deep, closed low sits just offshore of southern
Oregon and northern California this morning. With the Four-
Corners ridge extending north over the Intermountain West, swift
southerly upper-level flow has developed over the forecast area.
This has produced some downsloping flow in the Rogue Valley early
this morning, keeping temperatures warmer and humidity lower well
into the overnight period (temperatures didn`t drop to below 80
degrees until after midnight, and humidity has remained below 20%
through the time of this writing).

The low will push northeast beginning today, passing onshore north
of the mouth of the Columbia River by late Saturday. This will
result in cooler temperatures today through the rest of the
weekend, with daytime highs lowering to around normal for this
time of year, or around 10 degrees lower than yesterday. In what
basically amounts to the passage of a cold front, albeit a dry
one, winds are expected to increase today and Saturday while
humidity remains low for inland areas. This will result in
heightened fire weather concerns this afternoon and evening in the
Shasta Valley and for areas east of the Cascades. Saturday, as the
upper level flow shifts more southwest, the alignment with the
Shasta Valley ceases, so conditions will improve there. The Eats
Side, however, will remain windy and dry Saturday. A Red Flag
Warning is in place for these areas, with details available in the
fire discussion below, and at PDXRFWMFR.

The frontal passage will be a dry one, for the most part, but some
drizzle or very light rain is possible along the coast and in the
coastal ranges as the front interacts with the marine layer. There
is also a very slight chance (5-10%) 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., and the
most likely scenario will be some very isolated light showers or
virga.

By early next week, the cutoff low will be off to the northeast.
With southwest flow between another developing upper trough to
the northwest and ridging persisting to the southeast of the area,
next week is looking fairly uneventful, with continuing seasonal
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.

MARINE...Updated 100 AM PDT Friday, August 21, 2026...Light winds
and low seas will persist through the weekend. Some southerly
winds will increase today, then shift to westerly Saturday as a
weak front moves through the waters and passes onshore. A thermal
trough will develop by Sunday evening with stronger northerly
winds developing offshore. These winds will likely be hazardous to
smaller crafts Sunday night into Monday morning

-Smith

FIRE WEATHER...Updated 100 AM PDT Friday, August 21, 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.

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 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 as the front passes.
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 today and Saturday, mid-level
moisture increases today, 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, likely resulting in nothing more than
isolated very light showers, or more likely, just some virga. It`s
not impossible for isolated lightning, 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. The
convective threat pushes northeast of the area 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 this afternoon to 9 PM PDT this
     evening for ORZ624-625.

CA...Red Flag Warning from 2 PM this afternoon to 9 PM PDT this
     evening for CAZ281-284-285.

PACIFIC COASTAL WATERS...None.

&&

$$