651
FXUS66 KMFR 052145
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
245 PM PDT Thu Jun 5 2025

.DISCUSSION...Northerly flow will persist over the region today as
we remain on the back side of high pressure over the eastern
Pacific. Weak shortwaves have been passing through in this north
to northwesterly flow through the week, resulting in seasonable
conditions with periods of increased clouds along the coast and in
the Umpqua Basin. The last vestiges of this morning`s marine push
linger in the Umpqua Basin, but is quickly eroding this
afternoon. Meanwhile, cumulus fields are developing across the
East Side and the higher terrain of northern California. We don`t
expect much out of these cumulus clouds, but a stray shower can`t
be ruled out. Even then, it`s not likely for much, if any,
precipitation to reach the ground. Afternoon temperatures will
trend warmer today by a few degrees and we`ll see another round
breezy afternoon conditions.

This warming trend will continue Friday and through the weekend as
the upper level ridge over the eastern Pacific shifts eastward and
exerts it`s influence over the region. Meanwhile, energy from this
morning`s shortwave will undercut the ridge Friday and form a weak
cut off low off the coast of California just north of the Bay area
on Saturday. This low will nudge closer to the coast on Sunday
before passing overhead on Monday as a weak negatively tilted
trough. This overall pattern of ridge and weak trough offshore leads
to two main concerns for the weekend and into early next week: heat
and thunderstorms.

First the heat...As previously mentioned, the warming trend that
starts today will continue through the weekend, likely peaking on
Sunday. Hot temperatures are expected across the whole region
(except along the immediate coast) Saturday through Monday when
temperatures will be in the mid to upper 90s (upper 80s/low 90s)
west (east) of the Cascades. Near triple digits are possible on
Saturday and Monday for valleys west of the Cascades, with around a
60% of reaching or exceeding 100 degrees in the Rogue Valley on
Sunday. This heat could challenge a few records Saturday through
Monday with some locations forecast to tie daily high temperatures
during that time. One "fly in the ointment" regarding how hot
temperatures get is the potential for afternoon cloud cover from
showers and thunderstorms (more on that below). Increased cloud
cover could result in slightly cooler daytime highs, but could keep
overnight temperatures on the warmer side Sunday night into Monday
morning. Current HeatRisk values indicate a moderate risk of heat
related illnesses during this event, but given this is over a few
days and the first of the season, we may need to consider some heat
related headlines over the next few forecast cycles. Regardless,
those who are sensitive to this level of heat should take
precautions to prepare for these temperatures. And, if you decide to
cool off in area waterways, please remember that the water is still
very cold and currents are running swift. Make sure to wear a
life jacket and practice cold water safety!

Temperatures are likely to trend cooler from Tuesday onward. The
current forecast would bring temperatures more close to what we have
been experiencing this week.

On to thunderstorm potential...With a weak upper low off the coast
of California, we`ll be in a favorable pattern for thunderstorms,
especially Sunday into Monday as the trough becomes negatively
tilted and passes through the region. It should be noted that we are
looking at days 4-7, so there are likely to be changes to timing and
location of anticipated thunderstorms as we get closer in time. That
said, current guidance shows moist, unstable air moving into the
region beginning Saturday, then gradually increasing each day
through Monday. While moisture looks sufficient on Saturday,
instability and trigger are missing. As a result, cumulus buildups
are possible across northern California with a stray shower possible
(10%) around the Trinity Alps/Trinity Horn region. As moisture and
instability increase on Sunday, expect more widespread chances (15-
25%) of thunderstorms across Siskiyou and Modoc Counties and maybe
even as far north as southern Jackson/Klamath/Lake Counties Sunday
afternoon/evening.

The trough becomes negatively tilted and approaches the coast
overnight Sunday into Monday, and this could even bring the
potential for some nocturnal showers/thunderstorms. Again, there
could changes to timing/location, but at this time, the nocturnal
potential looks focused along an arc from central Siskiyou County
northwestward into Jackson/Josephine/Curry Counties. Even if nothing
happens during the overnight hours Sunday, convective activity could
get started across the West Side relatively early compared to normal
with moist/unstable air present early in the day Monday and the
upper trough acting as the trigger. At this time, we have a 15-30%
chance of showers/thunderstorms roughly from the Curry County
mountains eastward during the early afternoon hours on Monday.
Chances west of the Cascades diminish as the afternoon wanes, with
the focus transitioning to the East Side for late Monday
afternoon/evening. For now, gusty winds/outflows and small hail
(along with lightning, naturally) look to be the main threats with
these storms. Thunderstorm potential on Tuesday drops out of the
forecast for West Side locations, but lingers across portions of the
East Side and northern California. Then by Wednesday, things look to
stabilize more as we transition from this thunderstorm pattern to a
more zonal/weak troughing pattern. Again, stay tuned over the coming
days as this time frame draws closer and we hone in on
timing/location details. /BR-y

&&

.AVIATION...05/18Z TAFs...MVFR levels under marine stratus continue
for the Oregon coast north of Cape Blanco as well as the Umpqua
Valley. Improvement in these areas is visible on satellite imagery,
with a period of VFR levels expected late this morning. The coast
and the Umpqua Valley will see gusty winds, with marine stratus
rebuilding over North Bend. The Umpqua Valley may see some
development as well, but is expected to stay at VFR levels.

Other inland areas look to remain at VFR levels through the TAF
period. -TAD

&&

.MARINE...Updated 115 PM Thursday, June 5, 2025...With high
pressure offshore and a thermal trough near shore through tonight,
strong north winds will persist and maintain very steep and
hazardous wind driven seas from Cape Blanco southward. Meanwhile,
steep seas will persist north of Cape Blanco. North winds will be
strongest this afternoon and into the evening, reaching gales south
of Gold Beach between 5 and 40 nm offshore. Winds ease below gales
tonight, but very steep and hazardous seas will persist through
Saturday morning south of Cape Blanco.

The thermal trough pattern will be disrupted this weekend, leading
to weaker north winds and lower seas. The thermal trough returns
early next week with moderate to strong north winds and steep to
very steep wind-driven seas expected through mid-week. /BR-y

&&

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

PACIFIC COASTAL WATERS...Hazardous Seas Warning until 5 AM PDT
     Saturday for PZZ356-376.

Small Craft Advisory until 5 AM PDT Saturday for PZZ350-370.

     Gale Warning until 5 AM PDT Friday for PZZ356-376.

&&

$$

MNF/TAD