Onion Mountain Lookout, Oregon Weather Forecast Discussion

404
FXUS66 KMFR 081025
AFDMFR
Area Forecast Discussion
National Weather Service Medford OR
325 AM PDT Mon Sep 8 2025
.DISCUSSION...The pattern change we`ve been advertising for
several days now, finally arrives today. Early morning satellite
imagery shows the anticipated low pressure approaching the coast
this morning with lightning being observed within this system out
near 130 W. This low pressure will move inland today into Tuesday
and stick around through much of the week, resulting in widespread
showers with isolated to scattered thunderstorms and temperatures
more like early October through mid-week. Areas of degraded air
quality persist in southwest Oregon/northern California again this
morning, worst in the Rogue/Applegate/Klamath River Valleys.
Fortunately, the upcoming weather pattern is expected to dampen
fire activity (to what degree remains to be seen) and with less
fire activity, smoke concentrations should be less and generally
improved air quality is expected through at least mid-week.
Limited, local impacts could continue immediately downstream of
fires in eastern Curry/western Josephine/portions of western
Siskiyou Counties.
With low pressure directly overhead, this pattern will result in
several days of below normal temperatures. The "coolest" days of the
forecast period are expected to be Tuesday and Wednesday when high
temperatures bottom out around 10-15 degrees below normal. This
equates to mid 70s for West Side Valleys and mid-upper 60s for East
Side locations. Overnight temperatures, however, will still be
closer to normal for this time of year (50s west/40s east), likely
due to persistent cloud cover. Afternoon highs start trending warmer
on Thursday, but its not until Friday when we start seeing more
widespread highs back in the 80s (70s) west (east) of the Cascades.
Low pressure begins to move eastward on Friday with a shortwave
ridge building in Friday night into Saturday, resulting in
similar temperatures on Saturday compared to Friday.
In addition to cooler temperatures, we are confident that healthy
measurable rainfall will occur across the area during the first half
of the week. With low pressure overhead, precipitation will be more
showery in nature, so some areas could end up with less than others.
Despite this, nearly every single member from both the GFS and
European ensemble suite shows rainfall for multiple locations across
the region, including East Side and northern California points. As
low pressure moves inland, shower activity begins at the coast later
this morning, then spreads inland through the day today. Models are
indicating some instability and thunder potential in eastern Douglas
County/Cascades from Crater Lake northward around sunrise, so the
forecast includes this threat ahead of the main area of showers.
There will be day to day variations in precipitation amounts and
locations, but at this time, today looks like the day for the
highest amounts to occur along and west of the Cascades. Tuesday
features slightly less amounts and shifts eastward some to include
more of the East Side. Both of these days will include thunderstorm
potential with these showers, focused along/west of the Cascades on
Monday, then over much of the area on Tuesday.
There looks to be more of a break in precipitation Tuesday night,
but another round of showers/thunderstorms is expected Wednesday
afternoon. Again there will be a farther eastward shift with
precipitation focused along/east of the Cascades and across northern
California on Wednesday. A similar picture is forecast for Thursday,
though amounts look less compared to what`s in the forecast for
Wednesday. Precipitation chances diminish and conditions trend drier
as the day goes on Friday when the upper level trough transitions
eastward.
All in all, by the time we reach Friday, multi-day rainfall totals
are forecast to be in the 0.50-0.75" range along the coast, across
the West Side/northern California and even into portions of Klamath
County. 0.75"-1.00" is forecast in the Cascades and higher terrain
of the region, with upwards of 1.50" from Crater Lake northward. For
the far eastern areas in Lake and Modoc Counties, rainfall totals
are forecast to be in the 0.25-0.50" range, highest in the terrain.
With these totals in the forecast, this pattern is certainly
expected to be helpful with local firefighting efforts, and would
likely put a large dent in fire weather concerns.
&&
.AVIATION...08/12Z TAFs...VFR conditions will prevail across all
areas through this morning, including along the coast and over the
marine waters. Conditions lower to mainly MVFR in the late morning
and afternoon at the coast as low pressure approaches the region and
showers develop. VFR conditions will prevail for inland areas, even
as showers increase in coverage through the afternoon today, though
areas of mountain obscurations are likely. Moderate to heavy rain
rates may accompany showers with periods of lowered MVFR
visibilities. Embedded thunderstorms (15-30% chance) are expected
for inland area, including at Roseburg and Medford, especially in
the afternoon and early evening. Aside from lightning strikes,
locally heavy rainfall and gusty and erratic winds are possible
around thunderstorms.
&&
.MARINE...Updated 100 AM PDT Monday, September 8, 2025...Upper level
low pressure will move into the region today, bringing widespread
showers and isolated thunderstorms through this evening. Far less
shower activity is expected on Tuesday as this activity moves
inland. Sub-advisory conditions are likely to persist through at
least mid-week under light winds and low seas. South to southeast
winds today will turn northerly late tonight into Tuesday, then
persist through the end of the week.
Northerly winds should generally remain below advisory criteria
through the week, though could be a bit stronger in the favored
location south of Port Orford and between 5 and 30 nm from shore
during the afternoons Tuesday and Wednesday. While sub-advisory
conditions are likely to persist through the end of the week and
into the weekend, seas do increase some during the latter half of
the week (from 3-5 ft to 5-7 ft)as a low northwest swell (5-6 ft @
12-14 seconds) builds into the waters starting Thursday and
persisting into the weekend.
&&
.FIRE WEATHER...Updated 300 AM PDT Monday, September 8, 2025...The
anticipated pattern change arrives today and lingers over the region
through much of the week. This pattern will result in widespread
showers with isolated to scattered thunderstorms and temperatures
more like early October through mid-week.
Another round of gusty south to southwest winds is expected this
afternoon, and though we expect increasing daytime RHs today, lower
RHs (similar to what occurred over the weekend) are expected across
far eastern areas (Lake/Modoc Counties). We don`t anticipate any
areas of critical RH/winds overlap, so just noting that a moderated
fire weather environment will be slower to arrive for far eastern
areas compared to the remainder of the region.
With weather more typical of October that includes well below normal
temperatures, increasing daytime RHs, and widespread precipitation
chances, fire weather concerns will be minimal this week. Please see
the discussion above for temperature/precipitation details. While
daily thunderstorm chances are expected with this pattern, given the
ample moisture and moderated fire environment, we aren`t currently
planning on any headlines for the expected lightning activity.
&&
.MFR WATCHES/WARNINGS/ADVISORIES...
OR...None.
CA...None.
PACIFIC COASTAL WATERS...None.
&&
$$

NWS MFR Office Area Forecast Discussion