309
FXUS66 KMFR 110011
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
511 PM PDT Sat Aug 10 2024

.UPDATE...Updated the aviation section.


&&

.AVIATION (00Z TAFs)...Conditions early this evening are mainly VFR,
with areas of MVFR visibility reduction due to wildfire smoke

A marine layer will spread MVFR conditions into the coast and
coastal valleys north of Cape Blanco during this evening, including
at North Bend (KOTH) by 03Z. This is expected to persist through
around 18Z Sunday morning.

Meantime, inland TAF sites are expected to remain mostly VFR.
Wildfire smoke is thickest from eastern Douglas County into northern
Klamath County, and in southwest Siskiyou County. Smoke could cause
some minor visibility restrictions. Otherwise, typical afternoon and
evening breezes are expected with clear skies inland.
-DW

&&

.MARINE...Updated 230 PM Saturday, August 10, 2024...Northerly
winds are increasing, at advisory strength south of Cape Blanco with
steep seas. Wind speeds will peak Sunday afternoon, but steep seas
and strong northerly winds with conditions hazardous to small craft
will last through Sunday night.  The probability for wind gusts of
34 knots or greater south of Cape Blanco is roughly 40-60% where we
have the current Small Craft Advisory. Thereafter, winds and seas
will both ease through the middle of the week. -DW

&&

.PREV DISCUSSION... /Issued 252 PM PDT Sat Aug 10 2024/

DISCUSSION...An upper level trough is starting to develop over the
northwestern United States. While there will be some slight impacts
in the coming week, the forecast for the weekend remains stable.

Wildfire continues to be a concern. Homestead and Diamond complexes
in Douglas and Lake counties continue to put out ample wildfire
smoke. Early morning winds near the fires have a northerly
component, which can guide accumulated smoke south into west side
valleys or towards Klamath Falls. Afternoon winds increase in speed
and turn westerly, which will help to clear out accumulated smoke.
This also guides the smoke plume to the east, moving moderate to
heavy smoke over eastern Douglas and northern Klamath counties in the
late evening and early morning hours. The winds calm and turn
northerly, starting the pattern again. This pattern will also affect
movement of smoke from the Warner Peak fire (eastern Lake county)
and the Boise fire (Western Siskiyou county border).

As the trough deepens to start the week, daytime highs will fall
below seasonal averages for most of the area. The Oregon coast will
remain in the mid 60s to mid 70s. Areas west of the Cascades are
forecast to be in the lower to mid 80s and east side areas will
be in the upper 70s to lower 80s. These temperatures look to
continue through the week.

The trough will bring periods of instability as well. While forecast
moisture is not abundant, the combination of instability and what
mixture is forecast is enough to support slight (10-20%) Sunday
afternoon thunderstorm chances across Siskiyou, Klamath, and Lake
counties. Any rain that does fall is likely to be light, and
activity would mostly likely be isolated or scattered if anything
develops at all.

Considering long term conditions, there is some uncertainty on how
the trough will behave if it remains in place. But there is growing
agreement of a low pressure system moving into the trough and
possibly bringing some precipitation at the end of the week and into
the weekend. Amounts are slight, with the Oregon coast getting maybe
one-third of an inch and inland areas getting less (With one
ambitious ensemble member giving Medford over an inch of rain.
Optimism is wonderful). But any rain would be welcome. -TAD

&&

.FIRE WEATHER...Issued 200 AM Saturday August 10, 2024...After
another two days of above normal temperatures this weekend, the
forecast period will trend cooler through next week with
increasing onshore flow. The increased onshore flow will result in
improved humidities and overnight recoveries across the region,
especially for the coast, coastal valleys, Coquille and Umpqua
Basin, including the complex of fires in central and eastern
Douglas County.

Weak upper troughing is expected today with cooler afternoon
temperatures. There`s good agreement instability is marginal at
best, with little or no trigger and mid level moisture is lacking,
therefore the threat for thunderstorms are next to zero. The most
likely scenario will be cumulus build ups in the afternoon over the
Cascades and higher terrain east of the Cascades and northern Cal.

The potential for isolated thunderstorms will be higher Sunday as
the upper trough deepens, with increased mid level moisture and
stronger trigger ahead of the approaching upper low. Even then, they
will be isolated. There`s good agreement the best chance for
isolated storms will be centered over northern Fire Zones 624, 625
and portions of Fire zones 284 Sunday afternoon into Sunday evening.

General upper troughing will then remain over the area through next
week. Instability is marginal Monday afternoon east of the Cascades
and portions of northern Cal and some some evidence supporting a
slight chance of storms Monday, Wednesday and Thursday afternoon and
evening, but trigger is lacking and thus confidence is low we`ll get
any storms. For now we`ll keep a very low end chance (10%) of storms
for those days.

Also higher afternoon relative humidities are expected with fairly
good overnight recoveries, even for the eastside and northern
California. We`ll still have to deal with gusty breezes in the
afternoon and early evening hours, but with higher humidities in the
afternoons, we`re not expecting critical conditions. -Petrucelli/BPN

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...CA...None.

PACIFIC COASTAL WATERS...Small Craft Advisory until 2 AM PDT Monday
     for PZZ356-376.

&&

$$