Wildfire in Oregon, August 25 to 31, 2023

Area Forecast Discussion
National Weather Service Medford OR
250 PM PDT Fri Aug 25 2023

.DISCUSSION...A change from the very active pattern is in place
for most of the next seven days, giving fire agencies time to deal
with the hundreds of lightning strikes over the past handful of
days. There are a couple of days that may see some lightning in
the forecast, but the amounts and coverage of possible lightning
looks to be much less, and with the front moving through late
Monday/Tuesday portions of the forecast area may see showers
without any lightning. However, unfortunately Northern California
doe not look to be one these area at this time.

After today's break in the thunderstorm action the upper low off
the coast will bring some additional moisture and instability to
the far east side, and isolated thunderstorms are possible late
afternoon into the evening in Lake county tomorrow.

The GEFS spaghetti plots are in remarkably good agreement with the
depth and location of the upper low as it moves towards the shore,
opens to an upper trough and brings a front through late
Monday through Tuesday. there is instability indicated over the
northern Cascades Monday afternoon into the evening and the
northern east side a little east of the Cascades. However, mid
level moisture is indicated as anemic and will keep as slight
chance and evaluate further as we approach this time frame. as
this upper trough moves through the region instability is
indicated over the far east side, with area west showing more
stability. As we get closer models may change, but as of now
there looks to be a period of just showers from the southern coast
to the northern east side and areas north late Monday through
much of Tuesday. Below normal temperatures will also accompany
this system.

Models then begin to diverge as we head into the end of next week
with below normal temperature slowly rising to near normal as we
head into next weekend. -Sven

&&

.AVIATION...25/18Z TAFs...MVFR/IFR will continue for much of the
western half of Douglas and Siskiyou Counties as well as Curry,
Coos, Josephine, Jackson County including TAF sites (North Bend,
Roseburg, and Medford airports.) because of mist or smoke. The smoke
will continue through the TAF period with some fluctuation between
categories.

IFR coastal stratus are expected to lift this afternoon, while the
smoke will remain. However, the smoke make not reduce visibilities
too much at the North Bend Airport. Otherwise, the coastal stratus
and fog will return to the area, including at North Bend again
tonight. -Schaaf/BPN

&&

.MARINE...Updated 200 PM PDT...Weak low pressure with light south
winds will create calmer conditions which are likely to persist this
weekend into early next week. -Schaaf/BPN

&&

.FIRE WEATHER...Updated 200 PM PDT Friday, August 25, 2023...The
latest satellite image shows marine stratus along most of the coast
and into the coastal valleys, which has been sloe to burn off.
Meanwhile cumulus clouds are developing along and east of the
Cascades and a few over the Siskiyous. However, it won't ne nearly
as unstable as yesterday and mid level moisture is on the low side.
Thus, the chance for thunderstorms are pretty much zero.

Most of the forecast period will be dry through at least the middle
of next week. Saturday will be the only day where we could see an
isolated thunderstorm or two in fire zone 625. Guidance is
consistent across the board in showing elevated instability along
with increasing mid level moisture in fire zone 625. The trigger is
weak, but it could be enough for a storm or two to pop up late
Saturday afternoon into early Saturday evening.

Smoke remains pretty extensive in most of the interior westside
valleys, and it's not expected to improve much this afternoon and
early this evening. This will put a cap on the amount of wind we'll
see in the Rogue, Illinois, and Umpqua Basin. However the smoke is
not as extensive in the Shasta Valley, so we'll see breezy winds
there into early this evening. Elsewhere while we'll see breezy
winds, the combination of winds and relative humidities are expected
to remain above critical levels.

An upper level low will remain nearly stationary into the start of
next week, then will get kicked inland Monday night into Tuesday as
an upstream upper trough over the Gulf of Alaska moves east. This
will send a dry cold front into the area Tuesday.

The aforementioned upper low will swing into the area Tuesday and
this has the makings for moderate to strong winds along and east of
the Cascades Tuesday afternoon into early Tuesday evening. 700 mb
winds are not that impressive (20-25kts). However, 600 mb winds are
impressive (30-40 kts) and this is the time of the year when winds
could mix down near the surface from this level. In addition the
pressure gradient will be tight. The one limiting factor with
Tuesday will be the RH's. Right now were expecting to see a slight
uptick (slightly higher relative humidities) Tuesday afternoon which
could keep conditions above critical thresholds, but it will be
close. Even if critical thresholds are not met, any existent
holdover or smoldering fires from yesterdays lightning could "wake
up" and become active.

Weak upper troughing remains Wednesday, followed by another upper
low dropping south off the oregon coast Thursday, and possibly
getting cut off from the main flow by the end of next week. The
operational models differ with the position of the upper low late in
the week which could mean continued dry and stable conditions or
unstable enough for at least isolated thunderstorms. However the
ensemble means and clusters resemble the operational ECMWF keeping
the upper low positioned further offshore, thus lessing the threat
for thunderstorms. -Petrucelli

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...None.

CA...None.

PACIFIC COASTAL WATERS...None.

&&

SBN/SBN/SBN