Wildfire in California, July 5 to 22, 2018

Area Forecast Discussion
National Weather Service Medford OR
923 PM PDT Wed Jul 4 2018

.DISCUSSION...
No updates are needed this evening.

However, prior to the official start of the fireworks this
evening, we did have one rogue thunderstorm develop around 6 PM
PDT. Lightning detection indicated one in cloud lightning pulse,
and then one positive cloud to ground strike about 12 miles east
of Chemult. This cell then deteriorated as it drifted northward.

Also of note is that we did see some mostly elevated smoke over
the area today from about 5 large fires burning in northern
California. South winds brought this north, and this did appear
to aid cumulus cloud formation over portions of the forecast area
this afternoon and evening. We should expect more smoke aloft
tomorrow since the wind trajectories will be similar.

Tomorrow is expected to be similar to today, though even windier
and drier than it was today from the Shasta Valley eastward. Wind
advisories and red flag warnings remain in effect for tomorrow to
account for those expected conditions. BTL

&&

.AVIATION...For the 05/00Z TAFs...VFR conditions with scattered
cirrus will continue at all TAF locations with the exception of the
coast. KOTH has dropped to MVFR, and expect fog and low clouds to
bring conditions to IFR, and likely LIFR by early Thursday morning.
Gusty winds will continue east of the Cascades for a few more hours,
then diminish.

&&

.MARINE...Updated 900 PM PDT Wednesday 04 July 2018...Relatively
light south winds and mostly calm seas will continue tonight through
Friday night for most of the waters. Winds will reach 10 to 15 knots
Thursday afternoon. A period of gusty winds and elevated seas is
possible Thursday night and Friday beyond 40 NM from shore.
Northerly winds will return this weekend, with gales possible by
the middle of next week.

&&

.FIRE WEATHER...Updated 145 PM PDT Wednesday, 4 July 2018...Critical
fire weather is expected in the Shasta Valley of northern California
as strong south winds increases this afternoon. Models have been
very consistent with the idea of gusty to strong south winds this
afternoon through Friday with gust potential up to 45 mph and
humidity values 10 to 15 percent. A Red Flag Warning is in effect
for this. It's worth mentioning (given typical fireworks displays
this evening) that other areas will be very dry on this afternoon
and evening too, with humidity in the teens in valleys from
basically Interstate 5 eastward (and Western Siskiyou County).

On Thursday the south flow increases further over the east side, and
a Fire Weather Warning has been issued for the Shasta Valley
(FWZ281), portions of Modoc County(FWZ285), and portions of the East
Side(FWZ624).

Friday will be windy again east of the Cascades, and the winds and
humidities come close to, but are not expected to reach criteria
over the east side. However, we will continue to monitor and update
if need as we approach this time frame. Winds diminish across the
forecast area on Saturday as the upper trough moves inland and upper
ridging begins to build into the forecast area. There will also be
marginal instability over the far east side Friday, but with
extensive expected cloud cover we do not expect that it will warm up
enough for thunderstorm development.

Confidence continues to rise for a period of hotter temperatures
next week with continued dry conditions. The operational models and
the GFS ensemble members all show a ridge shifting westward into our
forecast area. This means a thermal trough and gusty north winds and
potentially lowering humidity could return as early as Monday to
coastal areas, including the Lobster Creek wildfire. -Sven

&&

.PREV DISCUSSION... /Issued 159 PM PDT Wed Jul 4 2018/

SHORT TERM...An upper low will remain offshore tonight and on
Thursday while an upper ridge centered to the east will gradually
strengthen. This will bring dry and warm conditions to inland
areas with cool and cloudy conditions along the coast. The high
clouds over inland areas are expected to decrease late this
evening into tonight as the upper ridge strengthens.

Strong and gusty south winds will continue in the Shasta Valley
this afternoon into this evening. Also expect gusty south to
southwest winds east of the Cascades through this evening with
gusts to around 25 to 35 mph. Winds are expected to peak late this
afternoon and early this evening. Dry humidities in the teens are
likely with these winds. This will create enhanced fire danger,
especially in the Shasta Valley where winds will be strongest. A
wind advisory and red flag warning are in effect for the Shasta
Valley area through this evening. Please see the NPWMFR and RFWMFR
for details. Dry humidities and some breezy west to northwest
winds are also likely in the western inland areas including
portions of Josephine, Jackson and eastern Douglas counties late
this afternoon and early this evening. Meanwhile, along the coast,
expect continued cool and cloudy conditions today. The coastal
stratus continues to affect some areas this afternoon and expect
these low clouds and patchy fog to increase along the coast and
into coastal valleys by late this evening into tonight.

Thursday, expect another day of warm and dry conditions inland
and cool and cloudy conditions along the coast. With the low
remaining off the coast, inland areas will see gusty south to
southwest winds again in the Shasta Valley and east of the
Cascades. This combined with dry humidities in the afternoon and
evening will bring another day of enhanced fire danger. Please see
the RFWMFR and NPWMFR for details on the winds and fire danger.

On Friday,  expect some moisture to move into southeast portions
of the CWA from the southwest as the upper low shifts
northeastward and moves inland as a trough over western
Washington. This moisture will bring mid to high clouds into the
area, especially east of the Cascades. There is a also slight
chance for a shower or two, mainly over eastern Lake County on Friday
afternoon. Stability parameters still indicate stable or only
marginally unstable conditions on Friday for east side areas and
model soundings indicate a dry subcloud layer with elevated cloud
bases. Given the stability, do not expect any thunderstorms to
develop. Will continue to monitor model forecasts for this period
though. Additionally, on Friday expect another day of gusty south
to southwest winds, especially east of the Cascades and in the
Shasta Valley.

LONG TERM...Saturday through Wednesday...Expect winds to be
lower on Saturday behind the upper trough. On Sunday, the area
will see a slight warming trend as a ridge build inland. This
ridge is short-lived though as another trough is forecast to
approach the Pacific Northwest coast Sunday night and move inland
over Washington and northwest Oregon on Monday. Tuesday through
Wednesday, models indicate that a stronger ridge may build inland
from the west and bring hot and dry weather to inland areas and
gusty winds along the coast, over the coastal mountains, and
across the coastal waters.

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Red Flag Warning from 1 PM to 8 PM PDT Thursday for ORZ624.

CA...Red Flag Warning from 1 PM to 8 PM PDT Thursday for CAZ281.
     Wind Advisory until 11 PM PDT this evening for CAZ081.
     Wind Advisory from noon to 11 PM PDT Thursday for CAZ081.
     Red Flag Warning from 1 PM to 8 PM PDT Thursday for CAZ285.

Pacific Coastal Waters...None.

BTL/MSM/SBN