179
FXUS66 KMFR 272101
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
201 PM PDT Wed Aug 27 2025

.DISCUSSION (Today through Tuesday)...

Overview:

Thunderstorm chances today will result in impacts across mainly
eastside areas where lightning over dry fuels will be a concern.
Please see the Fire Weather section below for more information.
Today is the last day in the current forecast with any rain
potential as the next several days appear to be dry into early
September. The dry weather will be combined with breezy to gusty
afternoons, so going forward we may still have fire weather concerns
across areas like the Shasta Valley and areas east of the Cascades.
Lastly, not seeing any particularly hot days which should keep the
heat risk down as we head into September.

Further Details:

We are currently hitting convective temperatures across eastside
areas based on forecast sounding data from earlier, and we have a
few cells developing updrafts with lightning noted via satellite.
Mean flow is generally weak today so cells will struggle to maintain
an updraft. Expecting these showers/storms to be closely tied to
peak heating, so these chances will exist through early this
evening. Not expecting widespread severe weather, but a few cells
could be strong with lightning and strong outflow gusts as the main
threats. DCAPE values are progged to be around 500-1500 J/kg which
is ample energy for strong momentum transfer to the surface.
Coverage is also expected to be overall isolated peaking between 3pm
and 8pm. Not expecting much--if any--activity beyond 10pm.

Main upper level feature going forward is an approaching and
deepening H5 trough. The main item of interest with this trough will
be the strengthening of the pressure gradient resulting in increased
wind speeds for most areas. We are not expecting precipitation with
this trough. Additionally, the mean flow will allow for wind speeds
to be enhanced through the Shasta Valley both tomorrow and Friday
via Venturi effects. This will be especially true through the
afternoon hours as deep mixing is expected. The eastside will also
see these increased speeds starting tomorrow and may see these
speeds continue to be elevated through the weekend. Not expecting
any wind hazards, but these conditions will play a role on fire
weather concerns which will be noted below in the Fire Weather
discussion.

Beyond Sunday, confidence drops with regards to some of the finer
details as the upper level pattern is showing some "odd" solutions.
Essentially we have a scenario with the GFS where the H5 low
retrogrades west and pivots around 46N and 130W before getting
absorbed into the mean flow. The pivot is an odd solution, and this
differs from the European model. We will have to see how the models
trend, but overall it doesn`t appear to have too much potential
change on the forecast. If somehow the pivot comes to fruition, it
may allow for an additional day of breezy to gusty winds early next
week.

-Guerrero

&&

.AVIATION (18Z TAFs)...

A marine layer along the coast will bring consistent MVFR/IFR
conditions with times of LIFR through this cycle. Inland sites
will be a different story with VFR conditions expected under
mostly clear skies. Thunderstorms (mainly) east of the Cascades
could bring impacts to Klamath Falls, but too hard to say with
much confidence if these will directly impact the terminal. For
now, have included a vicinity mention as it does appear isolated
storms are possible on the eastside today. Blow off from
thunderstorm updrafts on the eastside could bring high clouds over
Medford today.

-Guerrero

&&

.MARINE...Updated 200 PM PDT Wednesday, August 27, 2025...Relatively
calm winds and seas will persist through the end of the week.  After
the passage of a week system this weekend, the thermal trough will
redevelop along the coast, with gusty north winds and steep seas
returning Sunday, then persisting into early next week, especially
south of Cape Blanco.

-BPN

&&

.FIRE WEATHER...Updated 200 PM PDT Wednesday, August 26,
2025...Some slight cooling is expected over the next few days, but
highs are expected to remain above normal through Friday. Today
will be the last day of thunderstorm concerns for our area. Weak
upper level ridging returns Wednesday night into Thursday, cutting
off the moisture supply and bringing an end to the thunderstorm
threat.

Moisture continues to push up from the south into areas along and
east of the Cascades today, while somewhat drier air from the
north circulates down into areas to the west. This, along with
smoke from area wildfires, will limit thunderstorm chances today
to areas along and eats of the Cascades. A Red Flag Warning
remains in effect for these areas through this evening. Details
can be found at PDXRFWMFR. Given the high moisture content of the
atmosphere, these storms will be wet, and could produce heavy rain
within the cores, but could still produce gusty outflow winds of
up to 50 mph and abundant lightning outside those cores. Despite
the wet storms, numerous fire starts have been reported with the
thunderstorms of the past few days, and we believe this will
likely continue with any convection today.

Fortunately, today will be the last day of this multi-day
lightning threat as the monsoonal push comes to an end. On the
other hand, this will also lead to lowering humidities that will
coincide with continuing warm temperatures Thursday into Friday. A
building pressure gradient will result in breezy winds across
portions of western and central Siskiyou County Thursday and
Friday afternoons. With the drying humidities, these winds will
push conditions toward critical values for a few hours each
afternoon, particularly in the southern Shasta Valley and along
the ridges. Will not issue a Red Flag for these areas as the
criteria will not be met, but will highlight the conditions in the
forecast products.

Heading into the weekend, an upper level low will edge closer to
the coastline and pass to our northwest, allowing temperatures to
cool a bit more down towards seasonal normals, but also resulting
in breezier winds for the weekend. We will likely see enhanced
fire weather concerns due to low humidity and gusty winds this
weekend, and while we may approach headline thresholds, we do not
expect to reach critical conditions at this time.

-BPN

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Red Flag Warning until 9 PM PDT this evening for ORZ617-623>625.

CA...Red Flag Warning until 9 PM PDT this evening for CAZ281-284-285.

PACIFIC COASTAL WATERS...None.

&&

$$