Wildfire in Oregon, July 30 to 31, 2020

Area Forecast Discussion
National Weather Service Medford OR
849 AM PDT Thu Jul 30 2020

.UPDATE...

Forecast remains on track today with fog near the coast and
'clear' skies over the rest of the region. Smoke will continue to
impact southern Oregon and northern California with winds from the
south through today.

See the previous discussion below for more information beyond
today.

-Smith

&&

.DISCUSSION.../Issued 414 AM PDT Thu Jul 30 2020/
Our area of high pressure continues to be of
influence in our area. Current satellite imagery shows the
coastal stratus associated with the marine push just offshore and
along the coast of southern Oregon. A few patches of higher clouds
also exists through the area, but clear skies are the dominant
feature of this weather pattern. The thermal trough continues to
be inland today, and another round of hot temperatures are
expected in our area, even the coast will be a few degrees above
normal today with mainly clear skies. The exception to this will
be areas of smoke near wildfires in northern California and
southern Oregon. This smoke has further decreased air quality
across portions of these areas, including the Klamath Basin where
an Air Quality Alert is in effect through at least Friday.

A short wave will move through the area today, and could initiate
some cumulus clouds or even clouds that are in the beginning
stages of becoming a thunderstorms--particularly in the Cascades
from Crater Lake and northward and the northern portions of
Klamath and Lake Counties. A stray thunderstorm could be possible
in these areas, but much like last evening where nothing has
occurred, almost (if not all) the activity will be north of our
area.

Then, a series of dry cool fronts will begin to arrive on Friday.
This will bring more gusty winds to the area, especially east of
the Cascades. Additionally, this will bring cooler temperatures to
southern Oregon and northern California as well. Temperatures
will be much closer to normal (a 5-10 degree drop). These cooler
temperatures as well as dry conditions will continue through the
weekend into next week.

-Schaaf

&&

.AVIATION...For the 30/12Z TAF Cycle...Over the coastal waters and
along the coast...Areas of IFR/LIFR cigs/vsbys will continue through
this morning with locally dense fog, especially along the Curry
Coast. With lighter winds than previous days some areas may see
fog/stratus linger into the early afternoon.

Across inland areas...VFR conditions will prevail through today,
except for areas of MVFR vsbys and local IFR in smoke, especially
near active fires like the July complex near the Siskiyou/Modoc
county boundary and the Red Salmon fire, near Somes Bar, in
southwest Siskiyou County. Winds will be gusty again this afternoon
and evening.

-CC

&&

.MARINE...Updated 830 AM PDT Thursday 30 July 2020... Relatively
light winds and seas will prevail through this weekend. Winds will
shift to light southerly winds on Friday as a weak cold front
moves across the area. Winds will then become northerly Saturday
and Sunday. North winds will increase Monday into Tuesday with
gusty north winds and steep seas possible across the waters,
strongest winds and steepest seas south of Cape Blanco.

-CC/Keene

&&

.FIRE WEATHER...Updated 100 AM PDT Thursday 29 July 2020...This
week continues to be a critical week for fire weather across much
of the forecast area. Hot, dry, and breezy conditions will affect
the landscape through Friday, and at times the atmosphere will be
unstable, promoting growth on any new or existing fires.

First, thunderstorm potential. Some lightning is possible this
afternoon from Crater Lake northward and across northern Klamath
and Lake Counties. More likely, cumulus buildups will be possible
with the thunderstorm activity being north of the area (like what
occurred on Wednesday). The environment surrounding this energy
is very dry, but there could be just enough moisture in the middle
of the atmosphere for if a stray thunderstorm did form, it could be
dry. After this afternoon, thunderstorm potential should be
minimal to nil through Monday at least due to lack of moisture and
relatively stable conditions.

Next, gusty winds and low humidity. The two afternoons, through
Friday, will all be relatively similar. The Hot, Dry, and Windy
Index suggests this pattern will yield a top 5 percent event in
terms of how hot, dry, and breezy it is. This is especially
significant given the time of year, recent cloud to ground
lightning flashes, and the state of the fuels. We have decided to
extend the Red Flag Warning for portions of Fire Weather Zones
284...285...624...and 625 through Friday evening for
simplification because conditions will be so similar each of the
next 3 afternoons and evenings. One highlight for Thursday will be
a Haines Index of 6 for eastern Fire Weather Zone 284 and most of
Fire Weather Zones 285..624...and 625. This means dry and
unstable conditions that can lead to plume-dominated fires and
rapid fire growth of any new or existing fires.

Additionally, we expect breezy and dry conditions in the Scott and
Shasta Valleys the next two afternoons, though not quite reaching
Red Flag Criteria. For the Rogue Valley, slightly lower wind
speeds should be enough to prevent critical conditions from
occurring for the 2 hour duration, but things are still close
enough that we will be monitoring the situation closely.

-Schaaf/Keene

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Red Flag Warning until 8 PM PDT Friday for ORZ624.
     Red Flag Warning from 2 PM this afternoon to 8 PM PDT this
     evening for ORZ622.

CA...Red Flag Warning until 8 PM PDT Friday for CAZ284-285.

Pacific Coastal Waters...None.