Wildfire in California, August 19 to 31, 2020

Area Forecast Discussion
National Weather Service Medford OR
844 PM PDT Tue Aug 18 2020

.DISCUSSION...We've had a few thunderstorms in our area this
afternoon and evening, specifically over northern Lake County.
These storms did produce a decent number of lightning strikes, but
were nowhere near scattered in nature. Have gone ahead and
cancelled the Red Flag Warning for Oregon Fire Zone 625 for
abundant lightning on dry fuels that was supposed to go until 11
PM tonight. Overall, the thunderstorm threat has diminished in our
area; and although a stray thunderstorm is possible in the next
couple of hours, I would be surprised if we had anymore
thunderstorms tonight.

We start entering a more benign period of the forecast tonight,
with temperatures starting to drop to near normal. We still have
some gusty winds in the forecast tomorrow, especially for our
traditionally windy spots east of the Cascades, and have continued
our Red Flag Warning which occurs tomorrow at 2PM until 8PM for
strong gusty winds and low relative humidity for portions of
Oregon Fire Weather Zone 624 and California Fire Weather Zone 285.
(Parts of Klamath, Lake, and Modoc Counties).

Other than that, our forecast already reflects the nature of our
storms being isolated. And it does capture the locations of
expected smoke pretty well. Before sunset, we could see smoke
from the Red Salmon fire in Humboldt County lofting into the air.
We will continue to monitor that for any necessary changes, but
none are needed at this time. -Schaaf

&&

.AVIATION...For the 19/00Z TAFs...For the 18/00Z TAFs...Along the
coast and over the coastal waters...Areas of IFR cigs in marine
stratus will develop this evening, getting into the coastal valleys
tonight. The lower conditions will burn back to the coast by
Wednesday afternoon, then move back onshore Tuesday evening.

Inland...VFR conditions will prevail across most of the area through
Wednesday, except for southwest Siskiyou County, which will see some
reduced visibilities due to smoke from the Red Salmon Fire. Isolated
thunderstorms east of the Cascades will dissipate this evening.
Strong, gusty, erratic winds are expected with thunderstorms,
especially given the high based nature of these storms.

&&

.MARINE...Updated 800 PM PDT Tuesday 18 August 2020...Relatively
light winds and low seas will persist through Friday night. There
will be periods of poor visibility in low clouds and fog. A weak
front will move onshore Friday, then a thermal trough will develop
near the coast. This will bring increasing north winds to the area
Saturday into Sunday, with steep to very steep seas developing over
the waters.

&&

.PREV DISCUSSION... /Issued 218 PM PDT Tue Aug 18 2020/

DISCUSSION...As of 2 pm...Four corners high remains firmly in
place. High and midlevel clouds continue to stream northeast
across the region this afternoon...but have done little to keep
the heat away. Temperatures this afternoon were generally around 5
degrees above normal and are expected to warm another few degrees
by early evening.

All precipitation as of now remains to the east of the area.
However...the short term models continue to indicate the
possibility of showers and thunderstorms beginning early this
evening and continuing through around midnight. If we do see
thunderstorms...they will be mainly confined to Klamath County
eastward. Coverage will be pretty limited...however if storms do
form...there is the possibility a few stronger storms with
damaging winds and small hail.

Otherwise...an upper trough in the Gulf of Alaska will move west
toward the British Columbia coastline Wednesday into Thursday
morning...bringing a few degrees of cooling to the area. This will
also bring an end to our thunderstorm chances.

Continued subtle cooling is expected Thursday and Friday as an
upper low off of the British Columbia coast moves slightly south.
This will also bring the possibility of light rain to Coos County
and coastal Douglas County Thursday evening into Friday. If rain
does fall...we are not expecting much as far as accumulation.

The near normal temperatures Thursday and Friday will be short
lived as the four corners high begins to build northwest into
northern California and southern Oregon over the weekend.
Temperatures over the weekend will generally warm to 5 to 8
degrees above normal.

Not much change into early next week with no precipitation in
store for the area. According to the Climate Prediction Centers 8
to 14 day outlook...more of the same for the area with above
normal temperatures and below normal precipitation. Summer is in
full swing!

-Riley

FIRE WEATHER...Updated 200 PM PDT Tuesday 18 August 2020...

The main concern for the next couple of days will be isolated to
scattered thunderstorms into early this evening, then gusty winds
and low relative humidity tomorrow afternoon and evening. Details on
each will follow below.

The latest satellite image from a broader perspective shows a
moisture plume moving from south to southwest to north to northeast
over our area. From a more or less local scale, most of the clouds
are mid to high level, however underneath it there are signs of
cumulus build ups over the higher terrain in northern California and
Cascades east. As time goes on we can expect isolated storms to
develop in these areas early this afternoon. By late this afternoon,
there is a chance for scattered storms in northern and eastern Fire
weather zone 625. However given how dry things are in this area and
expected thunderstorms. The Red Flag warning includes the entire
zone. The steering flow this afternoon is not as strong compared to
yesterday, therefore were expecting the storms to move slower, but
there is still the risk for gusty and erratic winds near any
thunderstorms and small hail.

Isolated thunderstorms are expected to linger into this evening, but
the trend is for storms to gradually diminish, and ending by late
this evening.

After today, the threat for thunderstorms is close to if not zero
through the weekend. However the concern will shift from
thunderstorms to gusty winds and low relative humidity Wednesday
afternoon and early Wednesday evening. Right now, Fire Weather Zones
285 and 624 have the best chance for reaching criteria. The culprit
for this is due to a combination of an approaching upper trough,
stronger winds aloft (at least near 600mb) and tighter pressure
gradient. At the same time, the general consensus for the air mass
to dry out enough substantially with RHs back down in the 10-15%
range east of the Cascades and in portions of northern California,
particularly in portions of Fire Zone 285. SSW winds are expected to
increase in those areas with gusts exceeding 25 mph. This presents a
problem for any new fires that develop early this week, so the fire
weather watch has been upgraded to Red Flag Warning for southern 624
and 285 for strong, gusty winds and low RH. Please see RFWMFR for
more details.

Thursday, relative humidities will be a bit higher and winds a bit
lighter, so were not expecting Red Flag conditions to be met.
However this may be something we'll headline in the days to come.

Friday, a weak front will brush by north of our area, but could not
rule out intermittent light rain in fire zones 615 and northwest
616, but amounts will be light. The main effect will be cooler
temperatures over most of the area and higher relative humidities in
the afternoon.

A west to southwest flow remains over the area Saturday into early
next week with the strong upper ridge remaining southeast of our
area with the threat for thunderstorms almost zero and at least no
triple digit temperatures. -Petrucelli

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...     Red Flag Warning from 2 PM to 8 PM PDT Wednesday for ORZ624.

CA...Red Flag Warning from 2 PM to 8 PM PDT Wednesday for CAZ285.

Pacific Coastal Waters...None.