091
FXUS66 KMFR 162346
AFDMFR

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

.Updated AVIATION Discussion...

&&

.AVIATION...17/00Z TAFs...Along the coast and over the marine
waters, LIFR conditions under the marine layer will persist into
Thursday morning. Inland, expect VFR conditions to prevail through
the TAF period, though wildfire smoke/haze will bring reduced
visibility at times to Klamath Falls. Much like yesterday, cumulus
buildups mainly in the NorCal mountains and east of the Cascades
will continue through the evening today with just a stray (~10%
chance) of a thunderstorm. /BR-y

&&

.PREV DISCUSSION... /Issued 243 PM PDT Wed Jul 16 2025/

DISCUSSION (Today through Tuesday)...

Overview:

The general theme going forward is hot, dry, and breezy. Main impact
continues to be the heat as our heat related hazards continue
through this afternoon. That said, we are fortunately going to see a
trend of slightly cooler temperatures starting tomorrow, and we will
likely be back "down" to near normal highs by this weekend. Today is
the hottest day in the forecast for many westside areas (100-105),
and while temperatures are expected to cool off tomorrow, we will
still see highs around the upper 90s through Friday. Otherwise, we
are going to see haze/smoke impacts for the next few days as nearby
wildfires continue. Lastly, while its a low end chance (10%-20%), we
will see a potential for thunderstorms the next couple afternoons
(today through Friday). Smoke will likely add to inhibit these storm
chances, so we will need to monitor smoke/haze trends through these
next few afternoons.

Further Details:

Generally speaking, we have a northwesterly flow pattern aloft over
the PacNW with slight high pressure to the south of us. Model
agreement has a 500mb low strengthening over the Pacific around 37N
and 135W tonight. This will cause some disruption to the general NW
flow and may introduce some upper level dynamics over the forecast
area the next few afternoons. As we hit convective temperatures each
afternoon (today through Friday), we will have a very small chance
for thunderstorms each afternoon. This will be primarily for
northern California and areas east of the Cascades. These weak
forcing events are tough to forecast, but the smoke and haze in the
area does further confidence that thunderstorms are generally going
to struggle to mature. Most likely is we have towering cumulus that
struggle to develop into a thunderstorm. However, one cannot rule
out an isolated storm or two, with the best chance tomorrow
afternoon through this stretch. By better, this is only a 10-20
percent chance, so its a low end chance scenario. Tomorrow will have
the better instability (~300-500 J/kg), and better upper level
dynamics as the aforementioned H5 low brings PVA over the forecast
area, albeit weak forcing. Not expecting severe weather but
lightning and gusty winds will be possible with any thunderstorm
that develops.

The northwesterly flow pattern will essentially be unchanged through
the next several days. The airmass today will be the warmest, and a
generally decrease in temperatures are expected slightly each day
through Saturday. By Sunday, we will likely be close to normal
temperatures. For example, Medford is normally around the low/mid
90s this time of year, and we are forecasting 92 which is 1 degree
below normal. By Monday, there is a chance for westside valleys to
be below 90 with Medford currently forecast to be 89. These cooler
temperatures might be a nice welcoming for some folks after this
stretch of warm weather we have had.

While wind speeds are expected to be breezy (sustained 15-25 mph)
for some areas and in very typical diurnal fashion, we are not
seeing any days where wind speeds are expected to be strong.

-Guerrero

FIRE WEATHER...Updated 230 PM PDT Wednesday, July 16, 2025...

We don`t have any thunderstorms in the official forecast, although
there is a 5-10% chance of cloud to ground lightning in western
Siskiyou County based on the latest forecast this afternoon.

Aside from thunderstorms, the west coast thermal trough
dissipates according to the inverted MSLP and 850mb charts as we
see deeper westerly flow this afternoon and evening.

This cooler onshore flow really shows up on temperature trends west
of the Cascades. Highs drop 5 to 10 degrees, especially around the
Umpqua basin. A short wave trough will move in and bring another
chance of thunderstorms which is covered in the discussion above.
Winds and relative humidities will bring some concerns in the
eastern portions of our forecast area. our local MOS guidance is
suggesting some wind gusts up to 30 mph over the exposed RAWS sites
east of the Cascades with near single digit minimum humidities. This
will remain headlined in our fire weather forecast discussion.

Friday is another day to watch out for as pressure gradients
tighten. High pressure in the Pacific and generally lower pressure
farther to the east should allow for some gusty winds east of the
Cascades. There is very little change in humidities, so concerns
remain elevated for fire weather conditions in south central Oregon.

There should be gradual improvement in fire weather conditions
Saturday and Sunday with a bigger improvement by Monday as minimum
humidities about 5 percent higher compared to what we`ve been
observing. The hot dry windy index also shows this trend with fire
weather conditions improving into the extended period.

-Smith

MARINE...Updated 130 PM PDT Wednesday, July 16, 2025...Steep seas
persist across all waters through tonight. However, as wind waves
transition to fresh swell through early tomorrow morning, there may
be a brief period of improved conditions starting tomorrow and
going through at least Friday. That said, a weak thermal trough
could return over weekend. Though winds are expected to be weaker
than the previous event, steeps seas and advisory level winds could
return south of Cape Blanco over the weekend.

&&

.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.

&&

$$