NWS Medford, OR wrote its last area forecast discussion before the first event at Aug 31, 2:08 PM PST, 9 hours 52 minutes earlier.
Area forecast discussion, Aug 31, 2:08 PM PST, 9 hours 52 minutes before
Area Forecast Discussion
National Weather Service Medford OR
308 PM PDT Sat Aug 31 2024
.SHORT TERM...
There are some cumulus build ups east of the Cascades this
afternoon. There is also a small fire burning west of Crescent
Lake within the Diamond Lake Complex. It looks like a new fire as
it is outside of all the existing fire perimeters. Not a lot of
smoke out there right now and flow remains southerly, so that
smoke should be moving away from us the next few days.
Most of the time producing the forecast today was spent looking
at thunderstorm potential today through Monday. The chances remain
fairly low as moisture is marginal. The HREF is not even putting
down a 10% contour for probability of lightning this afternoon
and Sunday afternoon. Furthermore, forecast soundings are very
dry with large inverted V soundings with LCLs around 12000-15000
feet. Potential instability is also low and around 100, which is
enough for a weak thunderstorm, but it's frankly not a lot of
instability. In any case, there are low probability of
thunderstorms east of the Cascades today through Monday with
Monday being the best day, although storms might be to our north.
It will also be a windy day in the Shasta Valley on Sunday
afternoon with winds gusting to 35 mph or perhaps up to 40 mph at
times. The winds around 9000 feet above sea level are aligned with
the valley at 35 knots, so we feel pretty confident about a gusty
day in that valley. The main impacts here are fire weather
related, although 45 mph wind gusts would be a wind advisory.
The windier day is Monday as the west to east pressure gradients
tighten across the forecast region. South westerly flow appears to
be strong and sustained winds should be around 20 to 25 mph Monday
afternoon with gusts up to 35 mph. Even with this upper level low
moving onshore, the models believe this air will be dry,
especially farther to the south. In addition, temperatures will
trend cooler with highs in the upper 80's in Medford.
-Smith
.LONG TERM...
After this low passes through the region, we'll see a thermal
trough build along the southern Oregon coastline Tuesday evening
into Wednesday morning. North east to east winds will be strong
over the Kalmiopsis wilderness with some easterly breezes over the
Cascades. This usually results in some warm temperatures in
Brookings for daytime highs and we're currently forecasting highs
in the upper 70's to lower 80's, although those could very well
trend higher in future forecasts.
Beyond Wednesday, nothing really stands out except for the warmer
than normal temperatures and high pressure building in towards the
end of the week. Temperatures aloft are around the 97th to 99th
percentile for this time of year.
The last thing worth mentioning is the GEFS showing a trough
approach the Oregon coastline late Thursday into early Friday,
although it appears to flatten out with minimal impacts to our
weather. The NBM is still keeping daytime highs in the upper 90's
and lower 100's for highs late this week.
-Smith
&&
.AVIATION (18Z TAFs)...Areas of mainly IFR marine stratus
will diminish in coverage into this afternoon. The stratus will
surge in to the coast and coastal valleys again early this evening
with a mix of IFR and LIFR. These lower conditions will be more
stubborn to clear on Sunday, with only some modest lifting and
thinning during the day.
Inland areas will remain at VFR, though with late afternoon and
early evening cumulus buildups above the highest terrain of the
Cascades and a few thunderstorms possible. On Sunday afternoon, a
similar scenario will develop slightly farther to the north and
east, with cumulus buildups and a few thunderstorms possible north
of Crater Lake and across far northern portions of Klamath and Lake
counties.
-DW
&&
.MARINE...Updated 200 PM Saturday, August 31, 2024...Low clouds and
fog will thicken this evening and persist into Monday. Light swell
dominated seas and light southerly winds are anticipated through the
weekend into early Monday. Increasing north winds accompany the
development of a thermal trough on Tuesday with steep to very steep
seas possible. There is also a low risk that this thermal through
will be strong enough to produce gale force wind gusts in the outer
waters south of Cape Blanco. Conditions should improve Wednesday
into Friday morning. Then, north winds may increase again Friday
into Saturday. -DW
&&
.FIRE WEATHER...Issued 200 PM Saturday August 31, 2024...Hot, dry
and unstable conditions with the thermal trough inland will persist
today. Today will be another hot day and daytime humidities will be
very dry for the interior, especially east of the Cascades. Low
teens, with single digit humidities East Side, will be common again
this afternoon and winds will trend a bit stronger. Despite this
upward trend in wind speeds, conditions look to remain just below
warning criteria, but it will be close with near critical conditions
expected, especially in the Shasta and Scott Valleys as well as the
Cascades. Meanwhile, recoveries will be moderate to poor across the
interior through Sunday morning, poorest along the ridges and east
of the Cascades. Additionally, with the thermal trough being inland,
unstable conditions have increased with high mixing heights and
steep lapse rates across much of the area. These conditions increase
the probability of new and existing fires to become plume-dominated.
While today will feature the most widespread unstable weather
conditions, unstable conditions will continue through Sunday as the
thermal trough shifts eastward.
The pattern transitions on Sunday as low pressure approaches the
region and moves east of the area by Tuesday. Winds continue the
upward trend on Sunday in response to this pattern change, but
humidities trend higher as well, though not by much. This could lead
to some wind/RH concerns for portions of the East Side as well as
the Shasta/Scott Valleys on Sunday. Similar conditions are expected
again on Monday, but RHs trend higher again, which should limit the
wind/RH concern to far eastern areas along and east of the Winter
Rim in Fire Weather Zones (FWZ) 624 and 625, maybe even portions of
the Modoc as well. This combination of the strongest winds occurring
Monday and lingering critical humidities in 624,625 and 285; have
issued a Fire Weather Watch for late Monday morning through Monday
evening.
The other item of concern will be thunderstorm potential. As has
been talked about for days now, this low pressure moving through
region will bring at least a slight chance for thunderstorms mainly
along and east of the Cascades today through Monday. At this point,
it looks like isolated coverage (5-15% chance) is the most likely
scenario, especially today and Sunday. The low will push will into
the area late Sunday night into early Monday, and this gives pause
to any nocturnal potential. Guidance shows minimal moisture
available at the mid-levels for thunderstorm initiation as a dry
slot moves into the area overnight Sunday. So at this time, we're
not concerned for nocturnal thunderstorms Sunday night. The low will
move overhead on Monday, and this will likely be the best chance for
thunderstorms, particularly along the Cascades and east of the
Cascades north of Highway 140. Confidence is low in this however, as
there isn't a deep layer of moisture coming in with this low. It
appears as if the more scattered coverage will be possible to our
north in Northeastern Oregon; but a few isolated storms may be
possible for portions of the Cascades and northern Klamath and Lake
Counties. Instability and trigger are certainly there, but the
availability of mid-level moisture is marginal. Once this timeframe
is included in the high resolution models (which only forecast out
to 48 hours, currently through Sunday night), we should have higher
confidence on timing, location, and coverage of thunderstorm
potential for Sunday night into Monday. -Schaaf/BR-y
&&
.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Fire Weather Watch from Monday morning through Monday evening
for ORZ624-625.
CA...Fire Weather Watch from Monday morning through Monday evening
for CAZ285.
PACIFIC COASTAL WATERS...None.
&&