926
FXUS66 KMFR 011009
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
309 AM PDT Mon Sep 1 2025

.DISCUSSION...

-Increasing confidence on thunderstorms on Tuesday, and possibly
 into Wednesday.

-Hazy/smoky conditions will continue to bring periods of degraded
 air quality through the forecast period.

With an upper ridge over the region and a low well to the
northwest off the coast of Washington, warm and dry conditions
will persist across inland areas today. Conditions will be similar
or slightly warmer than yesterday for most areas. Along the
coast, expect areas of morning low clouds and fog,  clearing in
the afternoon. For inland areas, afternoon breezes will be
enhanced east of the Cascades and in the Shasta/Scott Valleys
today and Monday, similar to what occurred yesterday afternoon
with gusts of 20 to 25 mph (and locally to 30 mph in the Shasta
Valley).

Smoke from area wildfires will continue affect portions of the
area, with greatest concentrations expected across western/central
Siskiyou County and Klamath County. An Air Quality Alert for
Klamath County, issued by the Oregon Department of Environmental
Quality, remains in effect through at least Tuesday morning. The
HRRR model continues to show a pattern of increased smoke across
western/central Siskiyou county in the afternoon and evening and
increased smoke in Klamath and northern Lake counties in the
evenings and overnight. Little change in this pattern is expected
on Tuesday. Valleys in Jackson and Josephine counties will also
see periods of smoke in the afternoon and evening, both from fires
to the south and from a recent fire, the Dads Creek fire in
southwest Douglas County.

On Tuesday, models and ensembles continue to show an upper level
disturbance moving up from the south and towards the area. This
will send mid and upper level moisture into the area, which combined
with daytime instability will bring chances for thunderstorms to
central and eastern portions of the area. The best chance for
thunderstorms to develop will be across northern California and
from the Cascades east (15-30% chance). High resolution models are
also indicating thunderstorms will move from southeast to
northwest into Jackson and Josephine counties. Currently, expect
mainly isolated thunderstorms for these areas. Additionally, there
is a low chance (10%) for storms to move into southern Douglas
County on Tuesday evening. The potential for storms west of the
Cascades in southwest Oregon will bear watching as this pattern
develops. Gusty outflow winds are expected near and with
thunderstorms on Tuesday.

As the shortwave disturbance gradually tracks northward over the
area Tuesday night, models indicate a slight chance (10-20%) for
continued isolated thunderstorms overnight, especially across
Oregon zones and Modoc county, where moisture and instability is
greatest. Of note, with the southeast to east flow, there is a low
chance (5-10%) for storms to shift into central or western
Douglas county during this period.

Then, Wednesday through Friday, there is a continued slight
chance for thunderstorms or showers. For Wednesday, the main
concern is with the track of the first shortwave as it moves
north. The ECMWF continues to be slower with this shortwave and
keeps in over the area Wednesday, with a potential (15-25%) for
thunderstorms, mainly from the Cascades east. Thursday and Friday,
additional weak disturbances moving up from the south and into
the area. The best chances (10-20%) for thunderstorms are expected
from the Cascades east during this period. Also late Friday into
Saturday, a low offshore nears the coast, which may allow for
showers and thunderstorms to develop across inland areas.
Temperatures will also trend less hot Friday into Saturday.

&&

.AVIATION...01/06Z TAFs...Marine stratus has returned to coastal
areas, bringing VFR levels. Guidance suggests ceilings staying at
this level, but periods of IFR levels are possible. These ceilings
look to clear out by late Monday morning or early in the afternoon.

VFR levels continue for inland areas. Smoke from area fires will
move over the Medford and Klamath Falls terminals through the day.
While smoke has not brought extended lower flight levels, periods of
lower visibility are possible in these areas. -TAD

&&

.MARINE...Updated 200 AM PDT Sunday, August 31, 2025...Northerly
winds will develop and strengthen to advisory levels south of
Cape Blanco late this morning and this. This will result in areas
of steep seas south of Cape Blanco that are expected to persist
into Tuesday evening. Conditions are expected to improve for the
latter half of the week as winds ease and seas lower.

&&


.FIRE WEATHER...Updated 200 AM PDT Monday, September 1,
2025...The area will remain under southwest flow today with an
upper low off the Washington coast and a upper level ridge
centered inland over the region. This will bring a warm and dry
pattern to the area. Temperatures will be similar or slightly
hotter than yesterday. Similar to yesterday, breezy to gusty
winds and dry humidities are expected across inland valleys again
today, with strongest winds in the Shasta Valley and east of the
Cascades.  Overall, winds and humidities are not expected to
reach critical conditions. However, some locally, brief near
critical conditions are possible in the late afternoon and early
evening, mainly in the Shasta Valley and east of the Cascades.
So, we have continued to headlined the gusty winds and dry
humidities.

The upper level ridge will continue to strengthen on Tuesday and
Wednesday with hotter temperatures expected. Additionally, models
continue to show an upper level disturbance moving up from the
south towards the area on Tuesday. Confidence is increasing in
chances (15-30%) for isolated to scattered thunderstorms to
develop from the Cascades east and Siskiyou south Tuesday
afternoon and evening, and isolated storms to move into Josephine
and Jackson counties Tuesday evening. A fire weather watch remains
in effect for fire weather zones 280, 281, 284, 285, 617, 621,
623, 624, and 625 due to the potential for abundant lightning on
dry fuels. There is a potential for storms to move into zones 620
and 622 Tuesday evening. These storms are mainly expected to be
isolated but this will bear watching, as the track of the
shortwave favors storms tracking from southeast to northwest into
these areas. Additionally, models soundings show a very dry sub
layer (inverted "V" sounding) which means storms that do form will
likely produce strong, gusty and erratic outflow winds (35-50 mph)
and may produce little rainfall. As the disturbance slowly shifts
northward over the area Tuesday night, there are chances for
lingering overnight showers and thunderstorms (15-20%), mainly
from the Cascades east. However, with east to southeasterly
steering winds, storms may drift into western portions of the
area (10% chance), such as over Douglas County, on Tuesday night.


Wednesday, the operational models differ with the progression of the
upper low. The ECMWF has the low positioned in northern California
as it becomes cut off from the main flow. The GFS also hints at the
low becoming cut off from the main flow, but progresses the upper
low north of our area  Wednesday afternoon, which would put the
best chance for storms north of our forecast area. In contrast the
ECMWF solution would at least maintain the chance for
thunderstorms Wednesday afternoon and evening. So, have kept
chances for thunderstorms (10-25%) in the forecast for areas from
the Cascades east on Wednesday but confidence in the details is
low.

If the upper low does end up progressing slower, then we could be
dealing with the potential for nocturnal storms Wednesday night, but
much will depend on the timing and location of the upper low.

Isolated storms (10-20% chance) could still be a part of the
equation Thursday afternoon and evening and again Friday as
additional disturbances move into the area. Late Friday into
Saturday, a low nears the coast and will bring less hot
temperatures but additional chances for showers and thunderstorms
over inland areas on Saturday.



&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Fire Weather Watch from Tuesday afternoon through Tuesday
     evening for ORZ617-621-623>625.

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

PACIFIC COASTAL WATERS...Small Craft Advisory from 11 AM this morning
     to 11 AM PDT Tuesday for PZZ356-376.

&&

$$