130
FXUS66 KMFR 312137
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
237 PM PDT Thu Jul 31 2025

.DISCUSSION...Thunderstorm activity is getting an earlier start
today. Lightning strikes are being observed from storms around
Crater Lake, in eastern Siskiyou County near Tennant, and in
southern Lake and Klamath Counties. So far activity is generally
staying over terrain, with most storms showing little to no movement
on radar. As the shortwave trough helping to spark this activity
moves northeast, thunderstorms may continue over northern Lake and
Klamath counties into the evening. Nocturnal thunderstorms are not
expected, and activity should calm down into tonight.

While the shortwave trough looks to be away from the area by Friday,
weaker shortwaves moving around an upper level low pressure system
in the Gulf of Alaska will support continuing thunderstorm chances
in the afternoon and evening on Friday and Saturday. For Friday,
forecast chances decrease to 20-30% and are generally within
Siskiyou, Klamath, and Lake counties. On Saturday, chances fall
further to 10-15% in northern Lake and Klamath counties as well as
the Mount Shasta region of Siskiyou County. Outside of thunderstorm
chances, warm and summery conditions look to continue to start the
weekend.

On Sunday, an upper trough looks to move over the area. The most
immediate impact will be bringing temperatures to below seasonal
levels across the area. Depending on the timing, this trough may
also support thunderstorm chances on Saturday and Sunday. These
thunderstorms would most likely be over the usual areas, including
along and east of the Cascades. Precipitation chances for other
areas are currently negligible. This trough may bring some
elevated winds to terrain east of the Cascades, but widespread
gusty winds are not in the forecast right now.

Behind the trough, warm summer temperatures look to return on
Tuesday. Without a low pressure system to provide instability, the
start of next week is currently looking uneventful. In the long term
forecast, NBM probabilistic guidance shows a warming trend into the
end of next week. Looking at Medford for example, chances for 100
degree daytime highs are at 40% on next Friday, rising to 65% by
next Sunday. -TAD

&&

.AVIATION...31/18Z TAFs...Marine stratus is keeping IFR and LIFR
levels in place along the Oregon coast. Periods of clearing and
gusty winds are possible this afternoon, with winds calming and the
stratus stabilizing again in the evening.

Inland areas look to generally stay at VFR levels, with isolated to
scattered thunderstorms possible east of the Cascades and over
northern California this afternoon and evening. Activity should
decrease into the night. Even isolated thunderstorms can bring
lightning strikes, gusty and erratic winds, and small hail or
locally heavy rainfall. -TAD


&&

.MARINE...Updated 200 PM PDT Thursday, July 31, 2025...Gusty
northerly winds under a thermal trough pattern continue over area
waters. The strongest winds are south of Cape Blanco and within
30 nm of shore. These winds look to sustain steep seas in that
area through Friday night. Seas south of Cape Blanco stay near
steep heights on Saturday, then look to stay below advisory levels
on Sunday and into the start of next week. -TAD

&&

.FIRE WEATHER...Updated 200 PM PDT Wednesday, July 30, 2025...The
main concern will be scattered to numerous thunderstorms late this
afternoon into this evening. Gusty erratic outflow winds are also a
concern near thunderstorms during the same time period.

Satellite image shows a negatively tilted upper trough over the
northern Sierras and is expected to migrate north this afternoon
through tonight. Satellite image also shows building cumulus along
the Cascades, portions of the eastside and northern California, with
isolated thunderstorms already developing in portions fire weather
zones 280, 281 and 284.

As the negatively tilted upper trough moves north, this will lead
lead to scattered to widespread thunderstorms across the region. We
expect storms as far west as the Illinois Valley later this
afternoon and evening, with the greatest coverage expected from the
Cascades eastward and across northern California, and a Red Flag
Warning remains in effect for all Fire zones away from the coast and
Fire zone 616 until 11 pm pdt.

The general consensus is for storms to become less frequent this
evening and diminishing in the overnight hours. Isolated storms will
still be a concern, but the latest guidance suggest the best chance
should be mainly confined to portions of fire zones 624 and 625.

Another round of scattered storms are possible Thursday, but unlike
today, the focus for storms will be in northern Cal, and along and
east of the Cascades. We`ll be in a less favorable dynamic region as
the trough will have shifted north of the area. The greatest
coverage is more likely to be where there isn`t cloud cover in the
morning, which at this time looks to be east of the Cascades and
across northern California. Isolated storms could sneak through the
cracks in portions of Fire zones 621 and 622 late Thursday afternoon,
and early this evening, but not enough to warrant a concern. Due to
the expected scattered storms, the Fire Weather Watch has been
upgraded to a Red Flag Warning. Please see RFWMFR for more details.

Friday, there`s good agreement another shortwave, with a slight
negative tilt is expected to move into the area during the time of
max heating and instability. The combination of the both plus a
trigger could be cause for concern to warrent another Fire Weather
Watch for portions of northern Cal and east of the Cascades Friday
afternoon into Friday evening. However, due to the two headlines
currently out, and that were still a few days out, we`ll wait until
the first Red Flag warning to end, then reevaluate the situation
either tonight or tomorrow morning to see if another headline is
needed. Stay tuned.

For the weekend, Saturday pretty much looks ho-hum in that any
storms should be isolated and confined to portions of Fire zones
280, 281, 624 and 625 late in the afternoon and early evening.

Sunday, there`s good agreement a stronger upper trough will move
into the area Sunday afternoon which could trigger thunderstorms
along and east of the Cascades and northern California. Another
concern for Sunday could also be moderate to occasionally strong
winds ahead of the upper trough Sunday afternoon. -Petrucelli


&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Red Flag Warning until 8 PM PDT this evening for ORZ623>625.

CA...Red Flag Warning until 8 PM PDT this evening for CAZ280-281-284-
     285.

PACIFIC COASTAL WATERS...Small Craft Advisory until 11 PM PDT Friday
     for PZZ356-376.

&&

$$

TAD/MAP