499
FXUS66 KMFR 082338
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
438 PM PDT Fri Aug 8 2025

...Updated the aviation section...

.AVIATION...09/00Z TAFs...A few patches of low clouds and fog may
briefly develop at the coast north of Cape Blanco, including the
Coquille Valley, early Saturday morning around 10Z to 15Z. Gusty
north winds continue near the coast this evening, and return for
Saturday afternoon and evening with peak gusts at North Bend/KOTH of
around 30 kt. Otherwise, skies will remain clear with fairly typical
afternoon/evening breezes over the interior. -DW

&&

.MARINE...Updated 200 PM PDT Friday, August 8, 2025...A thermal
trough will remain in place with moderate to strong winds and steep
to very steep, hazardous seas through this weekend. Winds will be
strongest south of Cape Blanco, with northerly gales expected during
the afternoons and evenings for areas south of Gold Beach the next
couple of days. Winds gradually ease on Sunday as the thermal trough
pushes inland, but seas are likely to remain steep to very steep and
hazardous into at least Sunday evening, if not into Monday. Beyond
Monday, hazardous conditions should be confined to the outer waters.
-Petrucelli

&&

.PREV DISCUSSION... /Issued 202 PM PDT Fri Aug 8 2025/

DISCUSSION...High pressure over the northeastern Pacific will
gradually nudge eastward this weekend while a thermal trough has
already developed along the coast. These two features will
influence our weather into early next week, bringing hot
temperatures through Tuesday and dry conditions through the
remainder of the forecast period. Temperatures will trend warmer
today, reaching values more typical for this time of year. The
more notable warm up already underway is along the coast south of
Cape Blanco where offshore flow has lead to the development of the
Chetco Effect. We expect hot temperatures to continue in the
Brookings area where current forecasts show mid to upper 80s, with
low 90s certainly in the realm of possibilities. Temperatures
have already reached 86 degrees at the Brookings Airport and a
Heat Advisory is in effect for the coastal areas south of Gold
Beach. For inland areas, temperatures will trend warmer by about 5
degrees each day today and Saturday. Additionally, the
orientation of the flow will lead to some gusty north to northeast
winds in the Umpqua Basin and Illinois Valley today and Saturday.
These increased winds combined with low daytime humidities could
lead to some heightened fire weather concerns and more details can
found in the Fire Weather Discussion below.

The Chetco Effect will ease on Sunday as the thermal trough pushes
inland and brings the return of onshore flow to the southern coast.
This will bring cooler temperatures to areas south of Cape Blanco,
but temperatures will really heat up for inland areas on Sunday.
Expect triple digits for the West Side Valleys on Sunday with low to
mid 90s for the East Side. Similar conditions are expected again on
Monday, though temperatures east of the Cascade trend upward by a
few degrees. The forecast maintains a high temperature of 106
degrees, both Sunday and Monday, but the chances of reaching 110
degrees in Medford still hovers around 25% for Monday (10% on
Sunday). We`ve upgraded the Extreme Heat Watch to Warnings and
Advisories for Sun/Mon where confidence was high enough, and those
details can be found at NPWMFR. It`s a little earlier than usual for
deciding on warnings, so stay tuned for potential
adjustments/modifications if needed. Given the rather persistent
pattern of near to below normal temperatures we`ve been experiencing
in the region, felt it was prudent to get the message out sooner
than later.

The coast north of Cape Blanco still looks to miss out on the
hottest of the hot, but temperatures in North Bend could reach into
the 80s on Sunday.

These upcoming temperatures put the region under a moderate to major
risk for heat related illnesses. On both Sunday and Monday, much of
the area west of the Cascades is forecast to see a major heat risk,
meaning that this level of heat will impact anyone without cooling
or hydration. Take steps now to prepare for this heat wave, and be
sure to know the signs of heat illnesses.

The good news is (if you`re not a fan of the heat) that guidance is
showing the strong upper ridge retrograding westward to between 170
and 150W Tue-Wed and that should allow an upper trough to swing
southeastward across British Columbia. Usually, around here in the
summer, heat waves end with thunderstorms. But since this upper
trough will be swinging through from the NW, the flow aloft in
advance of it never really becomes southerly enough to allow
moisture to come northward. As such, we`ll most likely see a dry
frontal passage. This will heighten fire weather concerns over the
area though, since it will turn quite breezy and humidity could
remain on the low side. It should drop temperatures back closer to
normal though, perhaps even a bit below normal for the middle to
latter part of next week. /BR-y/Spilde


FIRE WEATHER...Updated 200 PM PDT Friday, August 8, 2025...Dry
weather will continue for the next 7-10 days with thunderstorms
chances next to zero.

A surface thermal trough will remain locked in along the coast in
response to upper ridging building over the area. This will bring
warmer afternoon temperatures, highest with respect to normal over
far SW Oregon near the beaches around Brookings this afternoon and
tomorrow due to a Chetco effect. As of this writing Brookings is
already 85 degrees with relative humidity at 25 percent.

Breezy east to northeast winds have set up over the upper
slopes/ridges in southwest Oregon and NW portions of Fire Zone 280.
This will result in moderate to locally poor relative humidity
recoveries through Sunday morning. A few locations(in the coast
ranges of FWZ 618/619 and mtns of FWZ 280) could get close to
critical levels (E wind >=15 mph or gusts >=25 mph and RH <=30% for
2-4 hrs) tonight, with slightly less wind Saturday night, but it`s
not expected to exceed critical conditions, so we`ll continue to
headline it in the fire weather forecast. Meanwhile gusty afternoon
and early evening northeast breezes and low relative humidity are
likely in the Illinois Valley today and Saturday. The Rogue Valley
will have gusty northwest afternoon and early evening breezes with
low humidity today and Saturday. The combination of the two are
sufficient for a Red Flag Warning for this afternoon/evening and
again Saturday afternoon and evening. Please see RFWMFR for more
details.

Sunday and Monday, the thermal trough will shift inland over the
interior. This should shut off the wind component for the Rogue and
Illinois Valley, but these will be the hottest days for inland
locations with west side triple digit heat and in the 90s east side.
Relative humidities will still be low in the afternoons.

East winds should also weaken Sunday night with improved overnight
recoveries near and at the ridges in southwest Oregon and western
fire zone 280.

Some single digit humidities in the afternoon are possible for
portions of Fire zones 624, 625 and 285 today through early next
week.

There`s good agreement for the strong upper ridge to shift west of
the forecast area Tuesday through the end of next week with weak
upper troughing moving in. We are pretty confident this will not
result in any thunderstorms, but the tradeoff will be increasing
winds, and low relative humidities, especially east of the Cascades.
At this time, it`s too far out to determine if critical conditions
will be met, but it will be something we`ll keep a close watch on.
-Petrucelli

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Extreme Heat Warning from 8 AM Sunday to 2 AM PDT Tuesday for
     ORZ024-026.

     Heat Advisory from 8 AM Sunday to 2 AM PDT Tuesday for ORZ022-
     023-029.

     Red Flag Warning until 8 PM PDT this evening for ORZ620-622.

CA...Extreme Heat Warning from 8 AM Sunday to 2 AM PDT Tuesday for
     CAZ080-081.

     Heat Advisory from 8 AM Sunday to 2 AM PDT Tuesday for
     CAZ082>085.

PACIFIC COASTAL WATERS...Small Craft Advisory until 8 PM PDT Sunday
     for PZZ350-356-370.

     Hazardous Seas Warning until 8 PM PDT Sunday for PZZ356-376.

     Gale Warning until 5 AM PDT Sunday for PZZ376.

&&

$$