243
FXUS66 KMFR 232344
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
444 PM PDT Sat Aug 23 2025

.Updated AVIATION Discussion...

&&

.AVIATION...24/00Z TAFs...The marine layer continues to bring
IFR/LIFR conditions to the waters and just inland along the coast
north of Bandon. Inland, VFR conditions will prevail through the TAF
period with mid-high level clouds streaming south to north across
the area and isolated to scattered thunderstorms just east of the
Warners. Expect thunderstorm activity to diminish after sunset.
Along the coast, IFR/LIFR conditions will impact all coastal sites
later this evening and overnight, then peel back to just offshore
Sunday morning, much like today. More widespread thunderstorm
activity is expected on Sunday, with the focus expected to be south
of the Rogue-Umpqua Divide, east of the Cascades and across northern
California. /BR-y

&&

.PREV DISCUSSION... /Issued 200 PM PDT Sat Aug 23 2025/

DISCUSSION...Water vapor satellite image shows monsoonal moisture
moving up from the south. Earlier this morning mid and high level
clouds were already in the area and can sometimes be a precursor of
things to come. As of this writing, several lighting strikes have
already occurred, in portions of Lake County, with the first
lighting strike observed around 11 am pdt.

Keep in mid level moisture will only increase over time from later
this afternoon through Sunday. This will only heighten the concern
for thunderstorms as we get into Sunday afternoon and evening.

Isolated storms are expected to end early this evening east of the
Cascades, with most locations dry tonight. However, there are some
indications we could see isolated convective showers in portions of
Lake and Modoc County overnight tonight. For now we don`t have
thunder in the forecast for tonight, but the threat for thunder is
NOT zero.

Sunday will be an active day, as mid level moisture increases along
with increasing instability and trigger. Sunday has all the makings
for storms to break out as early as late in the morning, but
certainly will increase in activity as we get into the afternoon. The
bullseye for storms are expected to be along the Cascades,
Siskiyous, eastside and portions of northern California. West of the
Cascades, should remain dry and hot. However, some of the CAMS
(model radar reflectivity), SHREF and other instability parameters
suggest storms that form over the Siskiyous drift north into
portions of the Rogue Valley, or even form in portions of the Rogue
Valley. Storms that do form should be isolated from mid to late
Sunday afternoon into Sunday evening. One thing of note, storms
Sunday afternoon and evening will have a higher chance of
precipitation reaching the ground, but model soundings show a dry
sub layer, therefore rainfall amounts could be limited.

Instability Sunday night will be marginal, with plenty of moisture
and sufficient trigger to support nocturnal storms overnight Sunday
along and east of the Cascades.

Monday and Tuesday will basically be rinse and repeat, with
relatively quiet weather in the morning followed by increasing
showers and thunderstorms in the afternoon and early evening hours.

From mid next week on, we could see a change in the a pattern as a
stronger upper low from the Gulf of Alaska drops southeast towards
the PAC NW which could bring cooler temperatures and more stable
weather to the area. The operational models show a similar solution,
and the clusters also show a breakdown of the upper ridging, with
the upper low lurking offshore. -Petrucelli

MARINE...Updated 200 PM PDT Saturday, August 23,
2025...Relatively calm conditions conditions are expected through
Sunday within 30 nm of shore, but steep seas will continue beyond.
As the thermal trough briefly strengthens, north winds and steep
seas will spread to all area waters Sunday night into Monday, then
persist through at least Tuesday. The thermal trough will weaken
and winds and seas should ease mid to late next week. -BPN

FIRE WEATHER...Updated 200 PM PDT Saturday, August 23, 2025...Hot
and dry conditions will continue through the weekend, and although
some slight cooling is expected early next week, temperatures will
remain well above normal for several more days. Excessive heat
warnings and heat advisories remain in effect. Please see NPWMFR for
more details. Humidities will begin to slowly improve over the next
few days as monsoonal moisture flows into the region from the south,
but this also means that there will be a threat of thunderstorms
daily through at least the first half of next week.

A portion of the "Four Corners" high has reached northwestward into
our area, with today`s 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. Temperatures tomorrow will be very similar to today.

A few lightning strikes have already been recorded today over
portions of eastern Lake County. A few more storms are possible
today as monsoonal moisture continues to be pumped north into the
area. 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 south and east portions of Fire Zones
285, 624 and 625 this 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.

There`s some evidence supporting nocturnal thunderstorms overnight
tonight 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 in the form of a weak shortwave
passing across the area from south to north. 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.
Due to the more widespread lighting threat Sunday, a Red Flag
Warning has been issued for these most likely affected areas.
Details can be found at PDXRFWMFR.

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, but clouds may inhibit daytime
heating and therefore inhibit convective development. This puts a
great deal of uncertainty into the forecast, so we are holding off
on any additional headline issuances fro Monday. After Monday, we`ll
be sandwiched between the weakening ridge to the southeast and
general upper troughiness over the area. -BPN

&&

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

     Red Flag Warning from 1 PM to 9 PM PDT Sunday for ORZ621-
     623>625.

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

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

     Red Flag Warning from 1 PM to 9 PM PDT Sunday for CAZ280-281-284-
     285.

     Heat Advisory until 8 PM PDT this evening for CAZ082>085.

PACIFIC COASTAL WATERS...Small Craft Advisory from 5 PM Sunday to 11
     PM PDT Tuesday for PZZ350-356.

     Small Craft Advisory until 11 PM PDT Tuesday for PZZ370-376.

&&

$$