077
FXUS66 KMFR 221054
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
354 AM PDT Fri Aug 22 2025

.DISCUSSION...Satellite shows clear skies everywhere expect near
Coos Bay where marine stratus is developing.

The main areas of concern in the forecast are the return of heat and
rain/thunderstorms this weekend. As the ridge continues building
around the four corners, the heat will come to the area first.
Morning temperatures will trend slightly warmer this morning with
more west side lows back in the 60s and upper 40s/50s east. The
higher heat risk will come this afternoon with 90s east side and
upper 90s to low 100s west. Heat Advisories and Extreme Heat
Warnings have been issued starting this afternoon for all areas
except the coast as they will be reaching the 70s for the most
part. The drier conditions today will also bring fire weather
concerns. The relative humidities will be below 15% in west side
valleys, but the winds are the factor that may not meet the time
length required for fire weather products. Please see FWFMFR for
more details on the fire weather risk. The heat will continue for
the next several days with triple digit highs in the forecast for
the Rogue Valley through Tuesday. The highest heat risk will be
found today and tomorrow with a 100% chance to see 100 degrees in
the Rogue and Illinois valleys and a 75% chance in the Umpqua
Basin. Precautions need to be made to protect yourself from the
heat. Drink plenty of water, avoid peak heating between 10 AM and
4 PM, and stay in an air-conditioned room as much as possible.
Please see NPWMFR for more details.

The other piece is the rain/thunderstorm chances this weekend. This
has a better chance to begin Sunday as monsoonal moisture is making
its way in from the south with disturbances to the west. However,
there is a 5-15% chance Saturday afternoon/evening east of the
Cascades in Lake and Modoc counties because passing showers from
the south could clip this area.

For Sunday`s chances, it will mainly be east of the Cascades, and a
25-35% chance of thunder will be present in far eastern Modoc and
Lake counties. Monday afternoon chances expand farther west to
include most of Northern California and the Cascades with a 25-35%
chance for showers. Models are signaling at a potential for
nocturnal thunderstorms Sunday night in Lake County.

A 25-35% chance for thunderstorms exists Monday afternoon in central
and eastern Siskiyou County, Modoc County and southern Klamath and
Lake counties. This trend of afternoon chances continues each
afternoon through at least Thursday. However, temperatures will be
cooling a few degrees at a time Tuesday through Friday. This will be
monitored as models are not in as much agreement yet this far out.

&&

.AVIATION...22/12Z TAFs...VFR conditions prevail inland and will do
so through the TAF period. Along the coast north of Cape Blanco,
IFR/LIFR conditions in marine stratus are returning early this
morning. Conditions along the coast will improve to VFR by late
this morning. /BR-y/Hermansen

&&

.MARINE...Updated 230 AM PDT Friday, August 22, 2025...A thermal
trough will maintain gusty north winds and steep wind-driven seas
across all area waters through 5 AM. Winds ease today, with advisory
level winds retreating to the outer waters and south of Cape Blanco
after 5 AM. Winds ease even more so over the weekend, hovering near
advisory criteria in the outer waters, which may maintain steep seas
through the weekend and potentially into early next week. /BR-
y/Hermansen

&&

.FIRE WEATHER...Updated 230 AM PDT Friday, August 22,
2025...Two main concerns lie ahead in the forecast. First will be
hot afternoon temperatures for the interior starting today and
lasting through at least the early part of next week, and excessive
heat warnings and heat advisories remain in effect. Please see
NPWMFR for more details. Second will be the potential for
thunderstorms as early as Saturday afternoon, with storm potential
lasting into the first half of next week.

A portion of the four corners high will nudge northwestward into our
area today through Saturday with afternoon temperatures heating up
into triple digit territory for the interior westside valleys and
low to mid 90s east of the Cascades. Only the immediate coast will
be immune to the heat with afternoon temperatures near seasonal
norms along with moderate to strong winds, especially from Cape
Blanco north. At the same time overnight lows will be warm,
especially near and at the ridges, thus there will be little to no
overnight relief from the heat. While relative humidities will be
low, Friday afternoon and evening, winds are not expected to be
sufficient enough for critical conditions to be met for the interior
westside valleys and east of the Cascades. For now, we`ll just
headline for near critical conditions for portions of Fire Zone 622.

Saturday, monsoonal moisture will begin to move up from the south,
and move into the area towards max heating Saturday afternoon. The
trigger is weak, but the combination of temperatures reaching and
possibly exceeding their convective thresholds, weak trigger and
increasing mid level moisture does raise the concern for at least
isolated thunderstorms in portions of Fire Zones 285, 624 and 625 in
the afternoon and evening. If nothing else, would not be surprised
if isolated storms pops up over the mountains in the above mentioned
Fire Zones. Additionally, winds aloft will be light, therefore any
storms that pop up will be slow movers.

There`s some evidence supporting nocturnal thunderstorms overnight
Saturday as mid level moisture increases with a continued weak
trigger. Some of the models show convective feedback by way of
precipitation fields overnight Saturday.

Sunday, conditions are more favorable for thunderstorm development
as mid level moisture and instability continues to increase, along
with a weak to moderate trigger. Thunderstorms Sunday will impact
the same areas as Saturday. However, the Cascades and portions of
Fire zones 280 and 284 could be in play for storms. For now areas
west of the Cascades should be in the clear, but it`s not our of the
question a couple of storms could come off the mountains and slip
into the southern portions of Fire Zones 620 and 622 late Sunday
afternoon and evening. However with light steering winds, most
likely they will remain along the terrain. It`s also worth noting the
convective feedback (precipitation fields) is a bit more robust
Sunday afternoon and evening. Nocturnal storms could still be a part
of the equation Sunday night, but confidence on this is low.

Afternoon and early evening thunderstorms remain a concern for the
first half of next week as week. Monday, we`ll be under a south flow
with monsoonal moisture still being pushed into the area along with
marginal to moderate instability. After Monday, we`ll be sandwiched
between the weakening four corners high and general upper troughiness
over the area. -Petrucelli

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Extreme Heat Warning from 1 PM this afternoon to 8 PM PDT Monday
     for ORZ024-026.

     Heat Advisory from 1 PM this afternoon to 8 PM PDT Saturday for
     ORZ023-025-027>031.

CA...Extreme Heat Warning from 1 PM this afternoon to 8 PM PDT Monday
     for CAZ080-081.

     Heat Advisory from 1 PM this afternoon to 8 PM PDT Saturday for
     CAZ082>085.

PACIFIC COASTAL WATERS...Small Craft Advisory until 5 AM PDT Saturday
     for PZZ356-370-376.

     Small Craft Advisory until 5 AM PDT early this morning for
     PZZ350.

&&

$$