998
FXUS66 KMFR 292317
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
417 PM PDT Tue Jul 29 2025

.UPDATE...Aviation Discussion Updated.


&&

.AVIATION...30/00Z TAFs...IFR low clouds and patchy fog are expected
to return to the coast from Brookings southward and Cape Blanco
northward (as well as into the Coquille Valley) after 03Z this
evening and persist through around 17Z Wednesday morning. Areas of
MVFR are then expected to linger Wednesday afternoon along the
coast.

Inland, VFR levels look to continue through the TAF period. However,
isolated to scattered thunderstorms will develop this evening,
mainly from the Southern Oregon Cascades eastward and across
northern California. There is also a 10-15% chance for thunderstorms
into southern Josephine and Jackson counties. Any thunderstorms
could temporarily lower ceilings and/or visibility, but the main
risks with thunderstorms will be gusty outflow wind gusts, cloud to
ground lightning and small hail. A more active, thunderstorm episode
is expected to affect a broader portion of the area on Wednesday
afternoon and evening. Scattered to numerous storms will be possible
for all but the coast and northwest Douglas County.

&&

.PREV DISCUSSION... /Issued 328 PM PDT Tue Jul 29 2025/

DISCUSSION...The Storm Prediction Center has included Lake
County in a Marginal (5%) risk for severe downdraft winds (58 mph
or stronger) from scattered thunderstorms this afternoon and
evening. So far, thunderstorms have developed in far northwest
Nevada. That activity is expected to build into Lake County over
the next few hours, while scattered thunderstorms also develop
over northern California and from the southern Oregon Cascades
eastward. A focus for activity is expected east of the Cascades.
Meantime, a lesser, slight chance risk also extends into southern
and eastern Jackson County and eastern Douglas County to include
the Cascade foothills.

A series of troughs will continue tracking east-northeast into our
region through the end of the week. The broadest coverage is
expected on Wednesday afternoon/evening...from the Coast Range
eastward and across northern California. On Wednesday, storms are
expected to be most numerous for Siskiyou County, the southern
Oregon Cascades, and Klamath County.

Embedded shortwaves are forecast to continue isolated
thunderstorms overnight on Wednesday night into Thursday morning,
mainly from northern Lake County across northern Klamath County
into eastern and far northern Douglas County, but will go with a
slightly broader brush to extend the slight risk into central
Douglas (including Roseburg) and Coos counties.

On both Thursday and Friday, the late day scenario will resemble
that of today with scattered thunderstorms again expected from the
southern Oregon Siskiyou Mountains southward, and Cascades
eastward.

On Saturday, the long-lived broad trough that is now over the Gulf
of Alaska will finally make some southeastward progress. That
progress will be more pronounced Sunday before it tracks into
western Canada and northern Washington on Monday. This will
diminish the risk of thunderstorms west of the Cascades, with an
east side focus expected for Saturday and possibly also on Sunday.
Then, an overall eastward kick of the region of instability. A
long awaited day without thunderstorms in our area is likely for
Monday! ...with the potential for several consecutive days of a
stable air mass.

MARINE...Updated 200 PM PDT Tuesday, July 29, 2025...A thermal
trough will bring gusty northerly winds and steep seas between Port
Orford and Pistol River through this afternoon. The thermal trough
will strengthen slightly early this evening with steep seas expected
to expand over much of the waters south of Port Orford through
Wednesday evening.

Conditions briefly improve with low pressure in the area later
Wednesday night into Thursday. Slight strengthening of a 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. -DW

FIRE WEATHER...Updated 200 PM PDT Tuesday, July 29, 2025...The
attention remains on thunderstorm activity expected this week.
Temperatures, humidities, and breezy afternoon winds will all remain
near seasonable levels this week, so the main fire weather concern
will be daily thunderstorm chances. Shortwaves will continue moving
through in southerly flow through Thursday, with the strongest (a
negatively tilted trough) passing through early Wednesday into
Thursday morning. Thunderstorm coverage will ramp up today, peak on
Wednesday as the strongest trough passes through, then gradually
diminish in coverage Thursday into the weekend.

Another day of isolated to scattered thunderstorms is anticipated
this afternoon/evening, with the greatest coverage expected along
and east of the Cascades. The Storm Prediction Center does have
portions of Lake County in a Marginal risk (level 1 of 5) for wind
gusts up to 60 mph this afternoon. The more common scenario will be
gusty outflow winds of 25-40 mph. A Red Flag Warning is in effect
for the eastern portion of FWZ 623 and all of FWZs 624/625/285
through 11 pm tonight. Activity will diminish later tonight, and
while showers/lightning are generally not expected tonight into
Wednesday morning, there is about a 5 to 10% chance of something
lingering overnight. Agreement among the guidance is not the best on
where this possibility is, ranging from portions of northern
Lake/Klamath County to over the Umpqua Basin to over Del Norte
County.

Where guidance does really agree is on the potential for some early
morning showers/isolated thunderstorms moving into the Modoc
Wednesday. This will be associated with a shortwave coming up from
the Sierras, then spreading northwestward and strengthening, leading
to scattered to widespread thunderstorms across the region. We
expect storms as far west as the Illinois Valley Wednesday afternoon
and evening, with the greatest coverage expected from the Cascades
eastward and across northern California. We`ve upgraded the Fire
Weather Watch to a Red Flag Warning for many locations (FWZs
617/620/621/622/623/624/625/280/281/284/285) for this time frame (2p-
11p). There is still some uncertainty regarding overnight
thunderstorm potential for Wednesday night into Thursday morning.
Guidance has trended farther north with the shortwave that would
have maintained overnight activity, but a subtle shift in it`s
location could bring it back farther south. Given this change, there
is still enough uncertainty in the details to leave some areas as a
watch for Wednesday night into Thursday. We`ve left the watch for
FWZ 616, and carried a watch for FWZs 617/623/624/625 into Thursday
morning. The focus for concern still shifts to the northern portions
of these zones for the overnight period. Stay tuned for updates over
the next few shifts.

For the remainder of Thursday, we`ll see another day of scattered
potential as this shortwave is exiting the region. The current
forecast maintains similar conditions on Thursday, but there is some
uncertainty on how much thunderstorm coverage will materialize due
to any lingering cloud cover from overnight activity. Additionally,
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. The
West Side threat likely drops out of the picture for Thursday and
we`ve put up a new round of watches for the potential Thursday
coverage. Fire Weather Watches cover all of FWZs
623/624/625/280/281/284/285. Details on the various watches/warnings
can be found at RFWMFR.

What`s after Thursday? Activity should trend less from Friday
onward, however, guidance shows additional shortwaves moving through
in a westerly flow pattern. This would result in diminished chances
of storms west of the Cascades while maintaining thunderstorm
chances east of the Cascades and across northern California. On the
other hand, temperatures will remain near seasonal norms, if not a
few degrees below over the upcoming weekend. /BR-y

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Red Flag Warning from 2 PM to 11 PM PDT Wednesday for
     ORZ620>625.

     Fire Weather Watch from Wednesday evening through Thursday
     morning for ORZ616.

     Red Flag Warning from 2 PM to 11 PM PDT Wednesday for ORZ617.

     Red Flag Warning from 2 PM to 11 PM PDT Wednesday for
     ORZ623>625.

     Fire Weather Watch from Wednesday evening through Thursday
     evening for ORZ623>625.

     Fire Weather Watch from Wednesday evening through Thursday
     morning for ORZ617.

CA...Red Flag Warning from 2 PM to 11 PM PDT Wednesday for CAZ280-281-
     284-285.

     Fire Weather Watch from Thursday afternoon through Thursday
     evening for CAZ280-281-284-285.

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

&&

$$