000
FXUS66 KMFR 051157
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
457 AM PDT Fri Sep 5 2025

.DISCUSSION...Radar/satellite has been fairly active this morning
with an area of showers/thunderstorms over the Umpqua Basin
westward to the coast and over the marine waters north of Cape
Blanco. Models showed some elevated instability in this region,
and outflows moving westward from Thursday evening`s convection
combined with a shortwave moving through the region, realized this
elevated energy. Radar shows cells moving generally
northwestward, now northwest of Roseburg/North Bend and will
continue this trend through sunrise. There is measurable rainfall
with these cells, with some sites in the Umpqua Basin reporting a
few hundreths and the Roseburg airport picking up 0.28" as the
core of one of the cells moved directly over the airport. Over the
remainder of the area, quiet conditions continue. The marine
layer is well entrenched along the coast and into the coastal
valleys, and areas of drizzle are possible this morning with a
deep marine layer in place.

A cooling trend is expected to start today and continue into next
week, with high temperatures eventually reaching 10-15 degrees below
normal by early next week. Highs today will be around 5 degrees
cooler than yesterday for West Side Valleys with similar
temperatures for the rest of the area. Our daily thunderstorm
chances will continue today and into the weekend, with the focus of
activity this afternoon expected to be in the northern Cascades, and
southeastward into portions of Klamath/Lake/eastern Modoc counties.
Later this evening and overnight into Saturday morning, guidance
shows the potential for some overnight thunderstorms again west of
the Cascades. While none of the CAMs are showing activity tonight,
they also didn`t show the current activity. Considering this
morning`s activity lines up with model indicated elevated
instability, and models again show this for tonight combined with a
negatively tilted shortwave approaching and moving through the
region, it`s reasonable to believe that there will be thunderstorms
during the overnight period tonight. Isolated showers/thunderstorms
will be possible just about anywhere west of the Cascades, including
the coast and over the marine waters. Thunderstorm chances continue
into the daytime Saturday, focused along and east of the I-5
corridor. Expect another 5 degrees or so of cooling for afternoon
temperatures, including areas east of the Cascades and in northern
California.

Beyond Saturday, the parent trough that has drifted around over the
eastern Pacific firing shortwaves at us this week will finally move
onshore and stick around through most of next week. This pattern
change will result in below normal temperatures and several days
(roughly Sunday night through Wednesday) of light, but beneficial,
precipitation chances that would make the area feel more like
October than early September. It is still yet too early in the
season, and precipitation may be too spotty, to call this a season
ending event for area wildfires. That being said, we are more
confident that healthy measurable rainfall will occur across the
area over the first half of next week, which would definitely be
helpful with local firefighting efforts, and would put a large dent
in fire weather concerns. /BR-y/BPN

&&

.AVIATION...05/12Z TAFs...VFR conditions prevail for most of the
area and will do so through the TAF period. Along the coast and
offshore, LIFR conditions will persist through the morning.
Meanwhile, isolated thunderstorms continue to impact the marine
waters and coastal locations, including North Bend, north of Cape
Blanco. Storm activity should wane around sunrise. Overall
conditions should at least improve along the coast to MVFR, but may
not fully clear to VFR this afternoon. Any clearing will likely be
short lived with MVFR/IFR conditions returning by late
afternoon/early evening.

For inland locations, another round of scattered thunderstorms is
expected this afternoon and evening, with the greatest activity
expected along the northern Cascades and southeastward into
Klamath/Lake and eastern Modoc counties. Isolated storms are
possible west of the Cascades late tonight into early Saturday
morning.

&&

.MARINE...Updated 200 AM PDT Friday, September 5, 2025...Isolated
showers and thunderstorms will persist over the waters north of Cape
Blanco through this morning. While storms aren`t expected to be
strong, gusts of 25-30 mph are possible with any thunderstorm
outflows. North winds will continue to weaken today, with marine fog
and low clouds persisting for the next several days. An upper level
low will pass over the area late today into Saturday, with showers
and drizzle likely, and a stray thunderstorm or two possible.
Outside of potential showers/thunderstorms, expect generally calm
conditions with no significant swell and light winds becoming south
ahead of an area of low pressure moving onshore early next week.

&&

.FIRE WEATHER...Updated 300 AM PDT Friday, September 5, 2025...The
primary fire weather concern for through Saturday, possibly Sunday,
will be isolated to scattered thunderstorms in the
afternoons/evenings as well as potentially overnight. Persistent low
pressure over the eastern Pacific will continue to send shortwaves
into the area. One shortwave is moving through the region this
morning, and managed to kick off several isolated storms in the
Umpqua Basin and westward to along the coast from North Bend
northward. There has been some measurable rainfall with these cells
as the Roseburg airport recorded 0.28" with a cell moving directly
overhead. This activity will wane down around sunrise with the next
shortwave expected later today and overnight into Saturday. We
expect another round of scattered thunderstorms in the northern
Cascades and southeastward into Klamath/Lake/eastern Modoc counties.
There should be rainfall with these storms, but storm motion 20-25
kt from the southwest, so storms aren`t expected to linger and
strikes outside of storm cores will be a concern. A Red Flag Warning
is in effect for abundant lightning on dry fuels for Fire Weather
Zones (FWZs) 617/623/624/625 and eastern 285 from 1pm through 9pm
this evening.

Storms could develop over the West Side again tonight as the
shortwave becomes negatively tilted and moves overhead during the
overnight hours. Models frequently struggle with overnight
convection, but there are indications of elevated instability
focused along and east of the I-5 corridor tonight, though a slight
chance exists for anywhere west of the Cascades including all the
way to the coast. Additional shortwaves pass through the area during
the day Saturday, bringing elevated winds over terrain east of the
Cascades. Thunderstorm chances remain in the forecast for Saturday
afternoon/evening, again focused along and east of the I-5 corridor.
As we get to Sunday, the atmosphere stabilizes some, but isolated
thunderstorms are not out of the question for northern areas.

Meanwhile, temperatures will trend cooler from today onward, helping
to moderate daytime RHs. Persistent low pressure offshore will
finally move into the region next week, and the cooling trend
continues with afternoon highs expected to be 10-15 degrees below
normal for early to mid-week. Widespread chances of beneficial
rainfall are increasing for early to mid week, and while it seems
too early to say it`s a season ending event, if the current forecast
comes to fruition, it could be considered a season slowing event.

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Red Flag Warning from 1 PM this afternoon to 9 PM PDT this
     evening for ORZ617-623>625.

CA...Red Flag Warning from 1 PM this afternoon to 9 PM PDT this
     evening for CAZ285.

PACIFIC COASTAL WATERS...None.

&&

$$