554
FXUS66 KMFR 022123
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
223 PM PDT Sat Aug 2 2025

.DISCUSSION...Satellite imagery is showing cumulus developing over
the higher terrain from the Cascades/Siskiyous south and east this
afternoon. Isolated thunderstorms have already developed along the
usual arc from just NE of Crater Lake to Winter Rim and just east
of Lakeview. Instability will continue to generate isolated to
scattered thunderstorms this afternoon/evening as a weak impulse
shifts NNE through the area. Overall, we don`t expect it to be as
active as yesterday, but still enough to be on the lookout for a
few of the stronger cells, which could contain gusty outflow
winds, small hail and, of course, cloud to ground lightning.
Models show the weak shortwave moving NE of the area late this
evening, so we think activity will wane after sunset and end by
around 11 pm. Isolated shower or thunderstorm activity is
possible farther to the NE up into Pendleton`s forecast area past
that time. Marine layer stratus will move back into coastal areas
this evening and probably last into the morning hours again.

Meanwhile, a stronger upper trough that`s out around 140W has
already had a history of producing lightning out over the ocean.
This will make its way toward the coast on Sunday. Models show
good instability -- 500-1000 J/KG (and little or no convective
inhibition) in the same general areas from the NorCal Mtns NNE up
the Cascades and over to the East Side during the
afternoon/evening. Supported by a 70+ kt upper jet, this trough
will bring good forcing and moisture arriving from the SSW to
induce another round of isolated to scattered thunderstorms. Best
chance for scattered thunderstorms will be across northern Klamath
and Lake counties where effective shear values are in the 25-35kt
range. This will support stronger updrafts/storm maintenance and
inverted-v soundings will promote strong outflow wind gusts with
hail in the strongest cells. The SPC has introduced a marginal
risk for severe storms there with storm motions generally
carrying them NNE into Deschutes County. Over here on the west
side, the environment is generally less favorable for
thunderstorms since moisture will be more limited. Even so, an
isolated cell cannot be ruled out. If it were to occur, it`d be
most likely at the south end of the Rogue Valley (approx. 15%
probability). Afternoon W-NW breezes (10-20 mph, gusts to 30 mph)
are likely to pick up just about everywhere Sunday
afternoon/evening as the trough swings through.

Thunderstorms (mostly) drop out of the forecast for Monday as the
upper trough axis exits to the east. There is still a slight
chance of thunder in the far eastern zones, but that`s about it.

Overall, the first week of August is usually one of the hottest
times of the year and it`s also climatologically favored for
thunderstorms in the area. But, through the 8th, it`s looking
pretty benign with temperatures remaining around or even below
normal levels (along with a general dearth of thunderstorms).
Expect highs in the mid 80s to low 90s for the inland west side
valleys and generally in the upper 70s to mid 80s over the east
side. Another trough will swing into the area around mid week (Tue
night-Wed night) and this could even bring some light showers to
the coast (though chances are low at this time - mostly 25% or
less).

Models then show the potential for a heat wave setting up toward
next weekend. Much depends on just how quickly this mid week
trough exits the region to east, allowing the upper ridge, which
is expected to build out near 40N and 140W Friday, to flop over
into the PacNW Sat/Sun. This would bring increasing mid-level
warming and 850 temps supporting highs close to or even above
100F over west side valleys. NBM is showing 99F and 103F for
Sat/Sun, respectively. We`ll keep an eye on this for potential
heat-related products as we head through next week. -Spilde


&&

.AVIATION...02/18Z TAFs...A mix of IFR/MVFR marine stratus exists
north of Cape Blanco in portions of Coos/western Douglas counties,
with a small area also around Brookings late this morning. These
will erode to VFR in most areas this afternoon, but will return
during the late afternoon/evening, then continue overnight into
Sunday morning. Gusty north winds of 15-25kt are expected at the
beaches this afternoon, but will ease around/after sunset.

VFR conditions are expected inland through the TAF period. However,
we do expect isolated showers and thunderstorms this
afternoon/evening in Siskiyou, Klamath, and Lake counties. Lightning
and gusty/erratic winds with small hail and locally moderate to
heavy rainfall are expected with any storms today. Activity wanes
and shifts north of the area by late this evening. -Spilde

&&

.MARINE...Updated 200 PM PDT Saturday, August 2, 2025...A weak
thermal trough will maintain gusty north winds south of Cape Blanco
with a small area of steep, hazardous seas from around Nesika Beach
southward and out to about 35 NM from shore through this evening.
Other than a brief uptick in afternoon/evening north winds between
Port Orford and Brookings (out to around 30 NM from shore) through
midweek, we expect sub-advisory conditions with seas in the 5 ft or
less range. A slight increase in seas is possible at midweek as a
light northwest swell (4-6 ft @ 10-12 seconds) moves into the waters.
A stronger thermal trough could develop toward next weekend as
things heat up inland. This would bring the potential for stronger
north winds and steep seas over the coastal waters Friday through
Sunday. -Spilde

&&

.FIRE WEATHER...Updated 200 PM PDT Saturday, August 2, 2025...
Individual cumulus cells have begun to develop over Lake and
Klamath counties this afternoon. While both cloud to cloud and
cloud to ground strikes have been sensed, each individual cell is
fairly isolated short-lived so far so substantial lightning has
not occurred. This level of activity is expected through this
evening, with development in parts of Siskiyou County possible as
well. Activity should decrease later this evening.

An upper trough looks to bring cooler temperatures across the area
on Sunday, as well as periods of gusty winds over east side
terrain. While this trough looks mostly dry and low minimum RH
values are forecast, there is currently no critical overlap of
these conditions. The front`s passage does look to support another
round of thunderstorms on Sunday afternoon and evening. Chances
for isolated to scattered thunderstorms are in the forecast over
Siskiyou, Modoc, Lake, and Klamath counties in the afternoon, with
isolated thunderstorms possibly continuing into the night.
Elevated instability with the front may support more development
for some thunderstorms, especially in northern Lake and Klamath
counties. Current guidance is split on if developed storms will
occur in zones covered by this discussion (FW Zones 624, 625) or
into zones farther north. More developed storms are capable of
putting out more lightning, small to large hail, and stronger
erratic wind gusts. While atmospheric moisture values suggest
wetter storms continuing, higher wind speeds aloft may allow for
more storm movement and less chance for wetting rain to fall on a
particular area. While there are no full warnings for this period
at this time, Sunday remains a period of elevated fire weather
concern. Please check back for future updates on expected
activity.

Beyond Sunday, a stable atmospheric pattern looks to set up over
the area to start the week. While some slight thunderstorm
chances may linger in easternmost Lake County on Monday afternoon,
significant thunderstorm activity is not expected. A pattern
change on Wednesday could also bring some activity, but confidence
in this outcome is not high so far out. Stable weather, dry
conditions, and above average warmth could be present next
weekend. -TAD


&&

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

CA...None.

PACIFIC COASTAL WATERS...Small Craft Advisory until 2 AM PDT Sunday
     for PZZ356-376.

&&

$$

MAS/TAD