558
FXUS66 KMFR 222324
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
424 PM PDT Fri Aug 22 2025

.Updated AVIATION Discussion...

&&

.AVIATION...23/00Z TAFs...VFR conditions prevail across the region
this afternoon. IFR/LIFR conditions continue just offshore from Gold
Beach southward. Expect this layer to spread northward to at least
Port Orford and inland into coastal valleys overnight tonight. North
of Cape Blanco, LIFR conditions are expected to return again,
including at North Bend. Elsewhere, VFR will prevail throughout the
next 24 hours. /BR-y

&&

.PREV DISCUSSION... /Issued 201 PM PDT Fri Aug 22 2025/

DISCUSSION (Today through Thursday)...

Overview:

Main items of interest are below with no notable changes from
yesterday:

* Heat: A heat wave will start today and continue through early next
  week. Heat Advisories and Extreme Heat Warnings are in effect.
  Records are in jeopardy through this stretch as well.

* Rain/Thunderstorms: Increased chances starting tomorrow and
  continuing into next week. Widespread severe weather is not
  expected, but a couple storms could become strong with lightning
  and strong outflow winds (45-55mph) as the main hazards.

* Fire Weather: Not seeing any widespread overlap of both critical
  winds and RH for the needed hours of Red Flag criteria albeit
  today will be close for the Rogue Valley, but certainly lightning
  over dry fuels could warrant fire weather hazards as early as this
  weekend. Please see the Fire Weather discussion below for more
  information.

Further Details:

Model guidance continues to show a broad area of high pressure
consuming much of the southern CONUS today. This H5 high is
progged to move west and northwest through the weekend which will
result in height rises over our forecast area. This will result in
a very warm airmass with triple digit temperatures expected
through the weekend and potentially into early next week. Heat
Advisories and Extreme Heat Warnings are in effect. The peak of
the heat wave will be today through Sunday, and records will be
within reach for several of our official climate sites. Next week
the high starts to break down and will likely be replaced by more
of a trough patterns and south to southwest flow aloft.

The placement of the high pressure will allow for monsoonal
moisture to get pulled northward. At the same time, we will have
weak perturbations riding around the northern periphery of this
high pressure. The combination of upper level energy and moisture
could result in convection across far eastern parts of both Modoc
and Lake counties tomorrow. This chances will spread west and both
as each subsequent day passes. Saturday has the least areal
extent at this time, but this day also has the highest
uncertainty. Areas on the westside (mainly the Rogue Valley) could
see chances for thunderstorms around 10-20 percent. Not expected
much--if any-- activity west of the Rogue Valley or north or the
Umpqua Divide. Any shift in the high pressure could result in both
the energy aloft and moisture getting diverted in either a
positive or negative manner as far as precipitation chances go.
Will continue to monitor this threat. At this time, widespread
severe weather does not appear likely, but if a thunderstorm forms
it could become strong with lightning and strong outflow gusts
(45-55mph) as the main threats. These storms will likely be tied
to daytime heating, so these would likely be pop-up storms through
peak heating (2pm-8pm) as we reach convective temperatures. The
combination of convective temperatures and small impulses aloft
should be enough to trigger thunderstorms. Lastly, we will need to
monitor the unlikely (at this time) scenario for nocturnal
thunderstorms. Saturday/Sunday night could be the timeframe we see
this nocturnal threat, but this is a very low confidence
scenario.

-Guerrero

MARINE...Updated 200 PM PDT Friday, August 22, 2025...A thermal
trough will maintain gusty north winds and steep wind-driven seas
through tomorrow morning. Winds ease today, resulting in advisory
level conditions shifting to the outer waters, in addition to
areas south of Cape Blanco. Winds continue to ease through
tomorrow, hovering near advisory criteria across the outer waters,
which may maintain steep seas through the weekend, but at this
time no hazards are in place for the waters starting tomorrow.

FIRE WEATHER...Updated 200 PM 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 West Side
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, though it may be close for an hour
or two.

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 isolated thunderstorms in southeast portions
of Fire Zones 285, 624 and 625 in the afternoon and evening. If
nothing else, would not be surprised if an isolated storm pops up
over the Warner or Hart 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 and
into early Sunday morning, but chances a very low, and only
mentioned here for the sake of completion.

Sunday, conditions are more favorable for thunderstorm
development as mid level moisture and instability continues to
increase, along with a weak to moderate trigger. Thunderstorm
chances Sunday will be more widespread, covering nearly all of the
East Side and much of northern California. For now, areas west of
the Cascades should be in the clear, but it`s not out of the
question a couple of storms could come off the Siskiyou 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. 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 heat persists and moisture
continues to flow into the region. 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/BPN

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Extreme Heat Warning until 8 PM PDT Monday for ORZ024-026.

     Heat Advisory until 8 PM PDT Saturday for ORZ023-025-027>031.

CA...Extreme Heat Warning until 8 PM PDT Monday for CAZ080-081.

     Heat Advisory until 8 PM PDT Saturday for CAZ082>085.

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

&&

$$