Wildfire in California, September 1 to 26, 2024

Area Forecast Discussion
National Weather Service Sacramento CA
123 PM PDT Sat Aug 31 2024

.SYNOPSIS...
Generally seasonable and dry conditions are expected through
Labor Day, with hot temperatures and widespread Moderate HeatRisk
then returning from Tuesday through the end of the week.

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.Discussion...
Latest GOES-West visible satellite imagery as of early this
afternoon shows a plume of upper level smoke filtering northward
from the ongoing Coffee Pot fire in south-central California. This
may limit daytime heating by a degree or two, but high
temperatures by the end of the day are still expected to reach the
mid 90s to low triple digits across the Valley and foothills,
with 80s to 90s at higher elevations. Additionally, a subtle plume
of mid level moisture is streaming northward along the Sierra
this afternoon and may spur an isolated shower/thunderstorm along
the crest south of Highway 50. Current probabilities of shower or
thunderstorm development remain around 10% though.

Moving into Sunday, an upper level pattern shift is expected as a
trough currently churning over the eastern Pacific progresses
eastward toward the NorCal coast. This will introduce an
appreciable cool down to high temperatures in the 80s to mid 90s
for Valley and foothills locations for Sunday and Labor Day. As
the trough moves further inland on Sunday, south-southwesterly
winds are expected to increase across interior NorCal throughout
the day. Winds gusts of 15 to 25 mph are expected on Sunday as a
result, with 40% to 50% probabilities of wind gusts to 30 mph
across the northern Sacramento Valley. South-southwesterly winds
will likely remain breezy for Labor Day, but with the trough
generally centered over northern California, gusts will be more
localized.

The next upper level pattern shift is then expected to arrive by
Tuesday, with the ejecting trough giving way to rising heights
aloft toward the middle of the week. A period of breezier
northerly winds will be possible on Tuesday as the trough departs
the region. This will all result in a rapid warm up to above
normal high temperatures by Tuesday afternoon. Depending on the
timing of the trough ejection, some elevated fire weather concerns
may be possible if a combination of increasing northerly winds
and drying humidity values overlap.

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.EXTENDED DISCUSSION (Wednesday THROUGH Saturday)...
Ensemble guidance and cluster analysis continue to depict broad
upper level ridging over the western half of the US Wednesday
through Friday. This will lead to a quick onset of above-normal
temperatures and widespread triple digit daytime highs across the
Valley; And corresponds with widespread moderate HeatRisk with
localized areas of major through Saturday. The NBM is currently
indicating a 60-90% chance of temperatures exceeding 100 deg F
Wednesday through Friday. Probabilities come down slightly for
Saturday (only 30-50%) as models show the development of weak
upper level troughing along the Northern California coastline
disrupting the ridging aloft. But temperatures still look to be
trending 3 to 7 degrees above-normal with Valley/foothill highs in
the mid to upper 90s.

We'll also see daytime relative humidity values drop into the low
teens to low 20s through Saturday accompanied by fairly poor
overnight recoveries due to the lack of onshore flow. Winds at
this time will be light to breezy, but these combined hot and dry
conditions look to bring about elevated fire weather concerns to
the Valley and foothills mid to late next week.

&&

.AVIATION...

VFR conditions over interior NorCal next 24 hrs. Surface winds
mainly below 12 kts, except in the Vicinity of the Delta where
periodical southwesterly gusts 15-25 kts are expected. Local
southerly gusts up to 15 kts possible in the northern Sac Valley
from 22z to 02z today. There is also a 5-10% chance of an
isolated thunderstorm along the Sierra crest (south of HWY 50),
between 21z-01z.

&&

.STO WATCHES/WARNINGS/ADVISORIES...
None.
&&