970
FXUS66 KMFR 190509
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
1009 PM PDT Mon Aug 18 2025

.UPDATE...Updated Aviation Discussion.


&&

.AVIATION...19/06Z TAFs...VFR conditions are present areawide,
except local IFR/LIFR along the coast near Brookings. Marine stratus
and fog is expected to bring areas of IFR to LIFR levels along the
coast overnight, with clearing expected in the mid morning on
Tuesday morning. Elsewhere, VFR conditions are expected through the
TAF period.


&&

.PREV DISCUSSION... /Issued 225 PM PDT Mon Aug 18 2025/

DISCUSSION...Visible satellite is showing clouds generally
diminishing where it was overcast earlier this morning and the
clouds will continue to diminish the rest of the afternoon. Other
than some fair weather cumulus over the northern Cascades and
northern Klamath and northwest Lake County, it will be clear.

Dry weather will continue through the end of the week, with
temperatures heating up starting mid week and lasting through next
weekend.

Today and Tuesday, the upper trough with a stable southwest flow
will be present which will keep afternoon temperatures in check with
values near seasonal norms for the interior.

Southwest flow continues Wednesday. However, some of the operational
models show a weak shortwave reaching the southwest Oregon coast
Wednesday afternoon. The operational models differ with the strength
of the shortwave, with the GFS showing a stronger solution.
Instability is marginal and there are signs for an increase in mid
level moisture in the northern Cascades and northern Klamath County.
Given the shortwave will be coming in during max heating. this could
result in cumulus buildups in the above mentioned areas. Right now
we don`t have thunderstorms in the forecast, but if the timing of
the shortwave does not change in the next couple of model runs,
would not be surprised if an isolated thunderstorm or two breaks out
in the above mentioned areas. We`ll keep a close watch on this.

Thursday through the weekend. The four corners ridge will strengthen
and nudge into our area with continued dry weather. It will start to
heat up Wednesday with hot weather likely Thursday through next
weekend with afternoon highs in the upper 90s for the interior
valleys Thursday followed by triple digit readings Friday into next
weekend. East of the Cascades, it will be in the upper 80s to low
90s the latter part of next week into next weekend.

One thing we`ll have to watch closely is the potential for some
monsoonal moisture to make its way from the south into portions of
the Eastside starting as early as Friday into next weekend. Mid
level moisture increases some Friday, but at this time it`s not
sufficient enough to support thunderstorm development. Saturday and
Sunday, the mid level moisture increases and it could be on these
days (afternoon and early evening) where there are a few signs
pointing towards isolated thunderstorms east of the Cascades and
northern California. However, it`s way to early if there will be
sufficient moisture to support thunderstorms as details can change
in the day to come. Stay tuned. -Petrucelli

MARINE...Updated 200 PM PDT Monday, August 18, 2025...Conditions
are expected to remain relatively calm through Wednesday morning.
Wednesday afternoon into Thursday, the thermal trough will return
and persist into the weekend, with moderate to occasionally strong
north winds and steep seas, especially south of Cape Blanco.
-Petrucelli

FIRE WEATHER...Updated 200 PM PDT Monday, August 18, 2025...
Seasonal temperatures and drier conditions are forecast to start
this week. A southwest flow pattern will bring drier air aloft,
minimizing the chances of thunderstorms in the area. A weak
shortwave looks to move over the area on Wednesday, which may bring
some cumulus development and slight chances for afternoon and
evening activity.

High pressure centered over the Four Corners may influence the
area near the end of the week and into the weekend. Daytime highs
will be above seasonal norms on Thursday. Most west side valleys
(Excluding Umpqua Valley) will see temperatures near or just over
100 degrees on Friday and Saturday. Overnight easterly winds may
bring periods of moderate to locally poor recoveries to area peaks
and ridgelines in this period, especially in Curry and western
Siskiyou counties. Atmospheric moisture is forecast to increase on
Saturday and early signals for convective thunderstorms are
appearing in guidance for Saturday and evening. In the absence of
more substantial forcing, activity would most likely be isolated
and remain east of the Cascades.

Long-term guidance starts to diverge on Sunday, but a slight drop in
temperatures is possible. Temperatures look to remain above seasonal
norms into the start of next week, with dry conditions continuing as
well. -TAD

&&

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

CA...None.

PACIFIC COASTAL WATERS...None.

&&

$$