102
FXUS66 KMFR 302123
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
223 PM PDT Wed Jul 30 2025

.DISCUSSION...With tsunami waves decreased below warning thresholds
in the late morning hours, attention turns to elevated thunderstorm
chances this afternoon into tonight. A negatively-tilted shortwave
trough associated with a low pressure system over the Gulf of Alaska
is moving over northern California and southern Oregon. This
shortwave trough will provide instability that looks to help fuel
scattered to widespread thunderstorms today. The highest chances for
thunderstorms (30-35%) are over Siskiyou County and the Cascades.
Chances are slightly lower in Modoc, Lake, and eastern Klamath
counties (25-30%), then lower again over Jackson and eastern Douglas
counties (20-25%) and Josephine County (15-20%). Precipitable Water
values look to be higher west of the Cascades at 0.85 in, with 0.65
in to the east. These values aren`t particularly exceptional, but do
indicate that areas east of the Cascades have a better chance of
seeing drier thunderstorms. Models have moved away from overnight
activity, although isolated thunderstorms over northern Lake and
Klamath counties are possible in the early Thursday morning hours.

With the shortwave trough still moving over the area on Thursday,
increased thunderstorm chances are in the forecast for the afternoon
and evening as well. That trough will have traveled to the
northeast, which puts the highest chances for activity (35-40%) in
northern Lake County. Lower chances (25-35%) are in the forecast for
Klamath, Modoc, Siskiyou, Jackson, and eastern Douglas counties.
With the shortwave trough on the way out of the area, Thursday`s
thunderstorms do not look to go into the nighttime hours. PW values
drop about 0.1 inches across the area on Thursday afternoon. Any
lingering cloud cover from today`s activity could further impact
Thursday`s thunderstorm chances.

Storm Prediction Center guidance does not indicate significant
severe thunderstorm chances for today and Thursday, but severe
activity is still possible. Even normal thunderstorms pose a number
of threatening conditions. Cloud-to-ground lightning, gusty and
erratic winds, small hail, and locally heavy rainfall may be present
under any active storm.

While the main shortwave trough will be absent after Thursday,
weaker shortwaves will continue to move over the area. Thunderstorm
chances remain in the forecast for Friday through Sunday, but are
currently lower (10-20%) and limited to northern California and east
of the Cascades. Warm summer temperatures and normal diurnal winds
will continue across the area through Saturday. A fast-moving upper
trough looks to bring slightly cooler temperatures on Sunday and
Monday before seasonally warm temperatures return in the middle of
next week. -TAD

&&

.AVIATION...30/18Z TAFs...While IFR levels continue at North Bend,
satellite imagery shows marine stratus trying to clear along the
Oregon coast. Guidance suggested marine clouds persisting through
most of the TAF period, but periods of VFR may occur along the coast
before marine stratus returns in the afternoon or evening.

Inland, VFR levels generally look to continue through the day.
Scattered to widespread thunderstorms will develop this afternoon
and evening across much of the area. This may bring temporarily
lower ceilings and/or visibility under active storm cells. The main
risks with thunderstorms will be gusty and erratic outflow winds,
cloud to ground lightning and small hail. Substantial nocturnal
thunderstorms look unlikely, but some lingering isolated cells over
Lake County are not impossible tonight. -TAD

&&

.MARINE...Updated 200 PM PDT Wednesday, July 30, 2025...A weak
thermal trough along the coast will maintain gusty north winds south
of Port Orford today. This is resulting in low end advisory level
winds and steep seas that will persist through this evening.
Conditions briefly improve with low pressure in the area later
tonight into Thursday. Slight strengthening of the thermal trough is
likely to bring a return of steep seas to the southern waters during
the afternoon and evening hours from Thursday afternoon into
Saturday evening. /BR-y

&&

.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 11 PM PDT this evening for ORZ620>622.

     Red Flag Warning until 11 PM PDT this evening for ORZ617.

     Red Flag Warning until 11 PM PDT this evening for ORZ623>625.

     Red Flag Warning from 2 PM to 8 PM PDT Thursday for ORZ623>625.

CA...Red Flag Warning until 11 PM PDT this evening for CAZ280-281-284-
     285.

     Red Flag Warning from 2 PM to 8 PM PDT Thursday for CAZ280-281-
     284-285.

PACIFIC COASTAL WATERS...Small Craft Advisory until 8 PM PDT this
     evening for PZZ356-376.

&&

$$