Continued periods of gusty offshore winds, dry conditions, and hot to record breaking temperatures allowed the August lightning fires to burn throughout the month of September. Persistent dry conditions across the hills and above normal temperatures made fire fighting efforts difficult with relatively poor humidity recoveries for much of the month.
Every event with a place to put it; 4 filed by county or forecast zone are drawn at its center, in a lighter ring. Tap one for its entry below.
Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.
The episode as NWS MTR wrote it up.
Continued periods of gusty offshore winds, dry conditions, and hot to record breaking temperatures allowed the August lightning fires to burn throughout the month of September. Persistent dry conditions across the hills and above normal temperatures made fire fighting efforts difficult with relatively poor humidity recoveries for much of the month.
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS San Francisco Bay Area, CA wrote its last area forecast discussion before the first event at Aug 31, 9:58 PM PST, 2 hours 2 minutes earlier.
Area Forecast Discussion
National Weather Service San Francisco Bay Area
1058 PM PDT Mon Aug 31 2020
.SYNOPSIS...Following today's passage of an upper level trough
through the Great Basin, an upper level ridge has begun building
into the Pacific Northwest. This will result in flow aloft over
our area turning weakly offshore later tonight into Monday
morning. The marine layer looks to remain entrenched however,
along with coastal stratus extending inland through the Bays night
and morning hours. Not much change in our weather conditions is
expected through the latter part of the week, but then significant
warming is possible next weekend into the first part of the
following week.
&&
.DISCUSSION...As of 09:15 PM PDT Monday...Fog product satellite
imagery shows stratus blanketing the coast and working its way
inland through the Bays, very similar to the same time Sunday
evening. Max Temps this afternoon weren't much changed from those
yesterday, aside from being a bit cooler in the North Bay Valleys
as coastal flow shifted to more out of the southwest. Latest
Bodega Bay and Ft Ord profiler data indicate a marine layer depth
of about 1200 to 1400 feet, also very similar to what it was 24
hours ago.
As discussed in greater detail below, longer range models do
continue to suggest the possibility of much warmer temperatures
next weekend into the start of the following week. Will note that
latest deterministic runs of both the ECMWF (12Z Monday) and GFS
(00Z Tuesday) take 850 mb temps at KOAK up to a max of almost 30
deg C in the time frame of next Monday to Tuesday, which is close
to all-time records for the month of September.
Have just updated the Tuesday Max Temp forecast to bring more in
line with highs observed today and latest model output and
guidance. Net result was a general lowering of values by 5 to 7
degrees, aside from the far southern interior of our district
where not much change is expected.
&&
.PREVIOUS DISCUSSION...As of 02:06 PM PDT Monday...Morning marine
layer did roll back to the coast this afternoon giving way to
inland sunshine. However, clouds never really cleared along the
immediate coastline and smoke/haze led to filtered sunshine
inland. The 24 hr temp trend little to change along the coast, but
slightly warmer this afternoon across the interior.
The forecast concerns/challenges over the next seven days are two
fold: near term concerns will be fire weather and longer range
concern will be excessive heat.
The longwave pattern is rather interesting as high pressure
remains parked off the PacNW Coast and low pressure remains off
the SoCal. The upper level high off the NW Coast is almost 600
DAM, which is somewhat unusual and several standard deviations
above normal. This upper ridge will slowly nose its was
southeastward into OR/CA. As this happens, the marine layer will
gradually compress and light offshore flow will develop for some
of the higher peaks. The latest hi-res models actually develop
some NE flow tonight and early Tuesday morning. SFO-WMC gradient
is near 10 mb, which is decent but not Red Flag Warning.
Heightened fire weather concerns are valid for at least the N Bay
Mts tonight.
Otherwise, forecast remains on track through at least Thursday.
Some minor day to day changes with a gradual compression of the
marine layer and warming of interior temperatures.
The next weather challenge is the expected heat next weekend. By
Friday the upper level ridge is firmly over the region and it will
be the first uptick in temperatures across the interior. 850mb
temps by this point are starting to eclipse 24-25C. That airmass
will translate to interior temps in the 90s. The trend will
continue even more over the weekend and peak on Sunday with 850mb
temps near 30C. Interior temperatures will be in the lower 100s
for Saturday/Sunday. Latest heat risk guidance shows possible
heat advisory for Saturday and then excessive heat warning for
Sunday. As the event draws near the outcome will become more
clear. As with most heat events the challenge will be the coast.
As of now, it appears the some onshore flow will remain keeping
temps in check.
Last but not least, smoke and haze will continue to be an issue
through out the week.
&&
.AVIATION...As of 10:55 PM PDT Monday...for the 06Z TAFs. MVFR to
IFR ceilings have returned to many of the region's terminals at
this hour given a marine layer between 1200-1400 ft in depth
(similar to 24 hours ago). Thus, confidence has increased with
respect to low clouds spreading back inland through early Tuesday
morning. The main question is how much of an impact haze and/or
smoke will be on visibilities through the forecast period. At
this time, all terminals are reporting P6SM with the potential to
lower slightly through the night. Conditions will gradually
improve between 16Z-18Z Tuesday for most terminals as stratus
dissipates and retreats to the coast.
Vicinity of KSFO...Increasing confidence for MVFR/IFR ceilings to
develop over the terminal early Tuesday morning with generally
light onshore flow. Look for low clouds to dissipate between
16Z-18Z with onshore flow increasing around 21Z.
SFO Bridge Approach...Similar to KSFO.
Monterey Bay Terminals...Well defined marine layer has resulted in
the return of IFR ceilings this evening which will likely lower to
LIFR late in the night. There is also the potential for lowering
visibility as well through early Tuesday morning. Conditions are
forecast improve between 16Z-18Z along with a slight increase in
onshore winds by midday Tuesday.
&&
.MARINE...as of 08:51 PM PDT Monday...Split flow prevails as a
weak low sits off of the coast with northwest winds over the far
northern offshore waters while lighter southerly winds persist
elsewhere. Generally light southerly winds will then prevail
through Tuesday before becoming northwesterly once again by
Wednesday night. Mixed seas will persist with a moderate period
northwest swell and longer period southerly swell.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
.Tday...None.
PUBLIC FORECAST: Blier/MM
AVIATION: RGass
MARINE: RGass
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www.youtube.com/nwsbayareaThe national radar mosaic for the moment the first event began.
6 wildfire. Local standard time, as filed.
The CZU Lightning Complex fires continued to burn through late September. The fire was contained on the 22nd with a total of 86,509 acres burned, 140 structures damaged, 1490 structures destroyed, 1 injury and 1 fatality in August.
The River Fire continued to burn through early September. A total of 48,088 acres burned with 30 structures destroyed, 13 damaged, and 4 injuries https://www.fire.ca.gov/incidents/2020/8/16/river-fire/.
The LNU Lightning Complex fires continued to burn through the month of September before being extinguished in early October https://www.fire.ca.gov/incidents/2020/8/17/lnu-lightning-complex-includes-hennessey-gamble-15-10-spanish-markley-13-4-11-16-walbridge/. A total of 363,220 acres burned with 232 structures damaged and over 1491 destroyed along with 5 fatalities (3 in Napa County and 2 in Solano County) including civilian and fire personnel across all counties. The LNU complex fire is now the 4th largest wildfire in California state history.
The SCU Lightning Complex fires continued to burn through September before full containment was reached on the morning of October 1st. The SCU fires became the third largest wildfire in California state history. A total of 396,624 acres burned, 26 structures damaged and 222 were destroyed, and 6 people were injured by the fire that spanned 5 counties https://www.fire.ca.gov/incidents/2020/8/18/scu-lightning-complex/.
The Carmel Fire that was sparked in August continued to burn into early September. A total of 6,905 acres were burned with 7 structures damaged and 73 destroyed https://www.fire.ca.gov/incidents/2020/8/18/carmel-fire/.
The Woodward Fire continued to burn throughout September before finally being extinguished in early October. A total of 4,929 acres burned with no structures damaged or destroyed https://www.fire.ca.gov/incidents/2020/8/18/woodward-fire/.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in California in 2020Every state in 2020This day in weather historyWarnings in California, September 2020
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 918120, 918121, 918122, 918123, 918124, 918125.