538
FXUS66 KMFR 161919
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
1219 PM PDT Wed Jul 16 2025

Updated AVIATION section

.DISCUSSION.../Issued 325 AM PDT Wed Jul 16 2025/Upper ridging
over the area will provide another hot day today with afternoon
temperatures averaging about 4-8F above normal in NorCal and over
the East Side, but as much as 10-12F above normal for the valleys
west of the Cascades. This means highs in the upper 90s and lower
100s for Medford, Roseburg, Grants Pass, and Yreka; and highs
generally 90-95F for Klamath Falls, Lakeview, Alturas, and Mount
Shasta City. A Heat Advisory remains in place for the west side
valleys, so if you`re planning to spend significant time outdoors
this afternoon, please try to stay hydrated and take frequent
breaks to cool off. Smoke from PacNW fires will cause haze and
even reduce visibility at times in the immediate vicinity/downwind
of the fires. Some areas may experience degraded air quality. A
weakness in the ridge will maintain some instability this
afternoon/evening, but forcing and moisture are limited. As such,
we`re expecting mostly just some cumulus buildups over the
mountains. Even so, much like yesterday, there is a low chance
(generally around 10%) a stray cell pops up, especially in the
NorCal mtns. Yesterday`s lone cell developed near Lava Beds
National Monument and did manage to produce 2 CG lightning
strikes. Marine layer is persistent along the coast and is
bringing widespread low clouds/fog from Florence to Brookings this
morning. These will peel back to the immediate coast later this
morning, but may only result in a few hours of sunshine. In fact,
some places (especially at the beaches) may hold the stratus all
day. It won`t be as breezy as it has been the last few days.

On Thursday, the ridge will continue to weaken. It`ll remain very
warm, with still some moderate heat risk for those sensitive to
heat. A minor disturbance will move northeastward across the area
during the afternoon. Mid-level winds increase to around 30kt in
advance of this feature and model CAPE is showing a few hundred
J/KG stretching from the mountains of Siskiyou County up into
portions of Klamath/Lake counties. We`ve bumped up the probability
of thunder in these areas and allowed for isolated thunderstorms
as most CAMs do produce at least some activity during the
afternoon/evening (2pm-10pm). This doesn`t look like a widespread
lightning outbreak, but we do expect a better chance than today.
Soundings are showing a well- mixed sub-cloud layer with
inverted-V profile, so any cells that do manage to get going will
have the ability to bring gusty outflows. Even without
thunderstorms, we expect breezy conditions to develop during the
afternoon/evening, highest in Modoc and into portions of Lake
County. Wind gusts could be 25-30 mph and this will coincide with
low RH values of around 10-15%. These conditions could approach
Red Flag, but we don`t think the area affected will be large
enough to warrant a warning.

Friday into this weekend, models are showing a couple of
disturbances moving southward across western Canada with a trough
axis pushing into the PacNW. This should at least take the edge
off the heat for most areas, though it will probably also result
in breezier afternoon/evening winds. Beyond that, guidance shows
one disturbance digging southward into Washington, which wold
further establish the trough early next week. We are confident
that this will drop temperatures to near or even a bit below
normal levels. But, it`s still a bit early to assess if this
trough will bring any precipitation. Time of year goes against
much, if anything, happening. But, at least a small percentage of
models do show some potential for convection across NE sections
of the CWA then. We`ll wait and see. -Spilde


&&

.AVIATION...16/18Z TAFs...The coastal stratus has cleared out this
morning and the main aviation hazard is now smoke from active
wildfires around the region. Northwest flow should help scape out
some of the smoke for locations west of the Cascades by this
evening. However, some thicker smoke could settle into areas east of
the Cascades with visibilities down to 2 miles near KLMT. Conditions
are anticipated to improve by Thursday with visibilities improving
across the board. However, smoke could settle into KLMT again.
There is also a very low chance of some cloud ground lightning in
the forecast area this afternoon.

-Smith


&&

.MARINE...Updated 230 AM PDT Wednesday, July 16, 2025...North
winds are weakening across the waters, but steep fresh swell will
persist through at least Thursday morning. Seas will become less
steep with a brief period of sub-advisory conditions possible on
Friday. Then, the thermal trough may return over the weekend,
though winds are expected to be weaker than what recently
occurred. Regardless, this could result in steep seas and advisory
level conditions south of Cape Blanco over the weekend. -Spilde

&&

.FIRE WEATHER.../Issued 325 AM PDT Wed Jul 16 2025/ Hot, dry
weather will continue today. While we do expect locally breezy
conditions this afternoon/evening, we don`t think it will be
sufficient for Red Flag. Overall, we`re expecting peak wind gusts
in the 20-25 mph range with minRH of 15-25% (locally lower from
around the Warner Mtns eastward). In terms of instability, similar
conditions exist today that occurred yesterday. We do expect a
few cumulus buildups, especially in the NorCal mountains, but with
generally a 10% chance or less of a thunderstorm. Mid-level winds
increase on Thursday as a minor disturbance advances
northeastward across the area. This will lead to a bit more in the
way of instability and a bit better chance of thunderstorms.
Isolated storms were added to the forecast in portions of Siskiyou
County (near, north/west of Mt Shasta), but the highest
probability (15-20%) exists along the Highway 97 corridor from
around Chiloquin northward and also eastward across
Klamath/northern Lake counties. Any cells that do develop will
have gusty outflows since soundings are showing a very well-mixed
and dry sub-cloud layer. Even in the absence of storms, for
locations SE of the the main thunder area, the increased mid-
level flow should mix down to the surface during the
afternoon/early evening. Local guidance is showing peak wind gusts
in the 25-30 mph range and some minRH down in the 10-15% range.
Once again, this will flirt with Red Flag criteria, but since it
will be mostly over a small area, we`ve decided to headline at the
top of the FWF instead.

This weekend into early next week, we`ll see a downward trend in
temperatures and slight uptick in humidity, but with daily
afternoon/evening breezes that will at least maintain elevated
fire weather concerns. We`ll monitor thunder potential with the
trough dropping down early next week. -Spilde

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Heat Advisory until 8 PM PDT this evening for ORZ023>026.

CA...Heat Advisory until 8 PM PDT this evening for CAZ080-081.

PACIFIC COASTAL WATERS...Small Craft Advisory until 5 AM PDT Thursday
     for PZZ350-356-370-376.

&&

$$