Wildfire in Oregon, July 5 to 31, 2021

Area Forecast Discussion
National Weather Service Medford OR
440 PM PDT Mon Jul 5 2021

Updated AVIATION Section

.DISCUSSION...Current satellite shows mainly clear skies across
southern Oregon and northern California. The exception is over
Brookings and offshore where marine status is overhead. A few fair
weather cumulus have started developing in Lake and Siskiyou
Counties as well. Overall, this is indicative of the area of high
pressure we're under as well as the thermal trough bringing hot,
dry, and breezy conditions. A heat advisory remains in effect for
portions of Jackson County and Western and Central Siskiyou County through
tomorrow evening. Meanwhile, the air quality alert for East Side
Valleys issued by Oregon DEQ is set to expire at 5PM today. These
remain on track, and with air quality remaining in the moderate
with occasional degradations to unhealthy for sensitive groups,
will wait for DEQ to reevaluate before keeping things ongoing.

The pattern begins to change tomorrow as a weak disturbance moves
across the Pacific Northwest. This will largely bring breezy winds
with slightly cooler temperatures across southern Oregon and
northern California. With extremely dry conditions, it will
prompt some fire weather concerns for portions of the east side,
so I recommend reading the fire weather portion of the discussion.
The other change that will occur is that some cumulus buildups
will be possible across portions of the Cascades north of Crater
Lake and Chemult and stretching eastward into portions of northern
Lake County. There is a slight chance that one of these cumulus
buildups could overachieve and put down a lightning strike.
Still, expect things to be isolated at best.

This change will be short lived with temperatures beginning to
increase as the next thermal trough builds and pushes inland this
weekend. It is likely that additional heat products will be
needed, but these will need to be evaluated and coordinated with
future shifts. Still, be prepared for the hot and dry conditions
to continue over the foreseeable future. -Schaaf

&&

.AVIATION...For the 06/00Z TAF Cycle...Much like yesterday, marine
stratus and fog has mostly shifted offshore this afternoon, except
for an area of IFR that extends from Pistol River southward. This
won't last long, however, as another marine push this evening
will spread inland into Coos and NW Douglas counties with IFR/MVFR
stratus/fog and continue overnight through Tuesday morning. This
will impact the terminal at North Bend, but should remain north and
west of Roseburg. Expect clearing to VFR back to the beaches or just
offshore Tuesday afternoon.

Over the remainder of the area...expect mainly VFR conditions with
areas of MVFR vsbys in smoke and haze across portions of southeast
Siskiyou County, southern Klamath, southern Lake and Modoc Counties.
-Spilde

&&

.MARINE...Updated 200 PM PDT Monday 5 July 2021...A thermal trough
along the southern Oregon coast will remain in place through today,
then weaken Tuesday before strengthening again Wednesday. Gusty north
winds and steep to very steep seas will persist through today with
the strongest winds and steepest seas from Gold Beach south. North
winds will weaken tonight into Tuesday but steep seas will persist
through Tuesday morning. Gusty north winds and steep to very steep
seas will return Wednesday and persist through Friday. The strongest
winds and steepest seas will occur south of Cape Blanco.

&&

.FIRE WEATHER...Updated 230 PM PDT Monday 5 July 2021...
The day-to-day changes in our weather during the next week look to
be mostly minor. A Red Flag Warning remains in effect for much of
Modoc County and a portion of far eastern Siskiyou County this
afternoon and evening. Have upgraded the more expansive Fire Weather
Watch to a Red Flag Warning for Tuesday afternoon. The Red Flag
Warning on Tuesday includes the same area but also larger swaths of
Modoc County and eastern Siskiyou County, and portions of eastern
Klamath and western Lake counties. Near critical conditions are
probable for a few hours Tuesday afternoon along and east of I-5 due
to moderate south winds and low RHs, but are unlikely to last for an
extended period of time.

Conditions will remain hot, very dry, and breezy inland this week
while night and morning marine pushes send stratus into the coastal
valleys. Winds will likely be strongest Tuesday ahead of an
approaching trough offshore. On Tuesday, this pattern should cause
enough instability to be sufficient for cumulus buildups and a
slight chance of isolated thunderstorms in Northern Klamath and
Lake County.

The upper level trough will result in a stronger marine push Tuesday
night with stratus likely to filter into the Umpqua Valley for
better humidity recovery. The trough will move inland Wednesday and
bring several degrees of cooling for Wednesday and Thursday. While
any improvement in conditions is welcome, the result will be inland
high temperatures that are still several degrees above normal.

This improvement will not be lasting. A ridge will quickly rebuild
Friday. Humidities may be at their lowest on Friday (Min RH
primarily 6-9% on the east side and 8-20% from the Cascades
westward) with a return of hotter temperatures into the weekend.

A continuing concern will be high Haines Indices in and around the
Lava and Tennant Fires. Both sites will mainly fluctuate between a
Haines of 5 and the maximum value of 6, highlighting the potential
for plume-dominated fire behavior. -Miles

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Red Flag Warning from 2 PM to 8 PM PDT Tuesday for ORZ624-625.
     Heat Advisory until 11 PM PDT Tuesday for ORZ026.

CA...Red Flag Warning from 2 PM to 8 PM PDT Tuesday for CAZ284-285.
     Heat Advisory until 11 PM PDT Tuesday for CAZ080-081.
     Red Flag Warning until 8 PM PDT this evening for CAZ284-285.

Pacific Coastal Waters...Small Craft Advisory until 11 AM PDT Tuesday for
     PZZ350-356-370-376.
     Hazardous Seas Warning until 5 PM PDT this afternoon for
     PZZ356-376.