A prolonged and oppressive heat wave swept the Central Coast and Bay Area for almost a week from August 14th to August 19th with widespread record breaking temperatures observed across the region. This was caused by a strong high pressure system over the Desert Southwest that expanded westward into California.
Every event with a place to put it; 8 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.
A prolonged and oppressive heat wave swept the Central Coast and Bay Area for almost a week from August 14th to August 19th with widespread record breaking temperatures observed across the region. This was caused by a strong high pressure system over the Desert Southwest that expanded westward into California. This dome of heat brought hot temperatures to the area for several days. Multiple days of triple digit afternoon highs were recorded inland with some coastal locations even reaching the mid 90s. Several days of hot and dry weather further dried fuels over the area increasing fire danger. During this event, a surge of monsoonal and tropical moisture from a former Tropical Storm advected northward with sufficient instability to generate multiple high based and dry thunderstorms that produced several thousand lightning strikes over the Greater Bay Area. Many locations saw wind gusts of 40-50 mph with isolated areas seeing gusts of 60-75 mph. This prompted the San Francisco Bay Area forecast office to issue a rare severe thunderstorm warning. These lightning strikes in combination with gusty and erratic outflow winds sparked hundreds of wildfires across the state of California. Several smaller fires combined to form complexes some of which are now among the largest wildfires in state history. Most of which were still actively burning at the end of August. Hundreds of thousands of acres have been burned with several hundred structures destroyed as well as a handful of deaths and injuries. Tens of thousands of residents were also forced to evacuate. Additionally, all of these wildfires burning simultaneously across the state gave the Bay Area the worst air quality in the world at one point.
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 14, 3:50 PM PST, 10 minutes earlier.
Area Forecast Discussion
National Weather Service San Francisco Bay Area
450 PM PDT Fri Aug 14 2020
.SYNOPSIS...Hot temperatures today with Excessive Heat Warnings
inland and Heat Advisories around the Bay as record or near record
heat develops. Little change through the weekend with continued
hot temperatures inland. Little relief along the coast as the
marine layer will be very shallow with only light onshore breezes.
The ridge responsible for the hot weather will stay in place
through early next week.
&&
.DISCUSSION...as of 1:56PM PDT Friday...The remnants of tropical
storm Elaida made for mid- to-upper level cloud cover over much of
our CWA this morning, along with muggy conditions that only added
to heat concerns that have played out throughout the day
Expecting the majority of this tropical moisture to depart our CWA
by Friday evening. The biggest concern for the next few days will
be this heatwave.
Record-breaking temps were observed today. We were off to a warm
start this morning all across the CWA, with mid-to-upper 70s F
already observed at several of our stations along the coast by
19Z. The marine layer is essentially non-existent, as the Fort Ord
profiler has captured its sharp compression over the last 24
hours. The upper-level ridge over the southwest has also settled
and expanded as was expected, resulting in >590dm heights across
the entire region. Interior locations earlier this morning such as
Livermore reached the mid-70s very early on, while poor
temperature recoveries from last night were also observed over our
higher elevation stations. All in all, do not expect the marine
layer to return for quite a while. Surface and near surface winds
have been light throughout the day, resulting in hot conditions
all the way into several of our coastal locations. We have also
seen locations all along the coast reach very high max temps
despite the cloud cover in the morning from the remnants of
Elaida. From our sounding we see than 850 hPa temps this morning
were also near 25 C over the Bay Area, which ended up translating
into today's hot conditions at the surface. Salinas has made it up
to 102 deg F as of this afternoon, while other locations like
Monterey and Carmel made it into the lower 90s by noon. A wind
shift did begin to occur around that time but unfortunately for
Salinas, the hot airmass overhead has made for no immediate cool
down despite the shift. Further up the coast, the SF Peninsula is
also experiencing warm conditions, while several higher elevation
locations in SF County like Twin Peaks and Mount Sutro are in the
mid-to-upper 90s F! 90s F are being observed throughout the East
and South Bays, with mid-90s widespread across the North Bay and
several locations past the 100 F mark, including Pinnacles which
is currently at 104 F. As for tonight, expecting warm min temps
across the CWA, especially in higher-elevation locations.
Expect poor temperature recoveries tonight and through tomorrow
morning, along with the added moisture tongue will result in
similar muggy and hot conditions all the way into the coast. There
does appear to be another moisture tongue that takes aim at the
Bay Area Saturday afternoon and through Sunday morning, with the
12Z GFS-20km run for today suggesting relatively moderate TTs
between 29 and 31 over interior locations of Monterey and San
Benito counties. Nevertheless, CAPE values are progged to be
lower than what we observed on Thursday. Should any convection
develop during that period, it is possible that it would follow a
similar setup to what was observed on Thursday with offshore
storms over our southern waters that made it ashore over our
southern CWA. The only other additional signature that both the
NAM and MTRWRF are currently hinting at outside of that area is
coastal Marin County. As such, any alterations to the current
parameters as newer runs come in between now and then could
significantly change the setup for that period. Should any cells
develop, the NAM and MTRWRF handled Thursday morning's setup
fairly well. In the meantime, not enough confidence to add
thunderstorms into the forecast for our inland locations.
In terms of convective potential for this weekend, there does
appear to be another moisture tongue that takes aim at the Bay
Area Saturday afternoon and through Sunday morning, with the 12Z
GFS- 20km run for today suggesting relatively moderate TTs between
29 and 31 over interior locations of Monterey and San Benito
counties. Nevertheless, CAPE values are progged to be lower than
what we observed on Thursday. Should any convection develop during
that period, it is possible that it would follow a similar setup
to what was observed on Thursday with offshore storms over our
southern waters that made it ashore over our southern CWA. The
only other additional signature that both the NAM and MTRWRF are
currently hinting at outside of that area is coastal Marin County.
As such, any alterations to the current parameters as newer runs
come in between now and then could significantly change the setup
for that period. Should any cells develop, the NAM and MTRWRF
handled Thursday morning's setup fairly well. In the meantime, not
enough confidence to add thunderstorms into the forecast for our
inland locations.
As a result of these conditions, it goes without saying that fire
weather will be something that will be closely monitored. Even
with the help of this tropical moisture today, several locations
observed low RH values. Following the next moisture plume on
Saturday, expecting hot and dry conditions to continue well into
the middle of next week. As such, these conditions coupled with
fuels are making for Statewide concerns over fires. We already
have 2 large fires in Northern and Southern California, and with
this heatwave affected most of California, will be keeping a close
eye on all fire weather concerns.
Looking ahead into next week, the latest NAM12km, GFS-20km, and
ECMWF Hi-Res runs for today are all suggesting that we can at the
very least expect 850mb temps around the 25 deg C range through
Tuesday of next week, with 96 + hour ranges of the GFS ensembles
and the ECMWF suggesting those temps to persist through Wednesday
as the Southwest Ridge builds to 597-599dm 500mb and gradually
centers itself deeper into Nevada. As such, there is a great deal
of confidence that this heat wave will be sticking around through
most of next week. As was observed today, coastal locations will
likely make it into the 80s, with some potentially once again
reaching the 90-mark. Not expecting conditions to be as hot as
today for the rest of the duration of the heatwave, but as it has
been emphasized already, the biggest challenge will be the
endurance owing to several days of hot conditions and poor
temperature and humidity recoveries. As such, expect hot locations
through the weekend and middle of next week as interior locations
will easily climb the mid-90s F, with up to 109 F in some of our
higher-elevation locations like Pinnacles. The most concerning
aspect with any sort of heatwave is the endurance required to deal
with persistent heat with little, if any, overnight temperature
recoveries. As such, will have to see when we extend heat products
and which areas will continue to be at risk as this heat wave
evolves through the weekend and into next week. Currently not
seeing any significant signature for offshore southerly reversal
in winds for this weekend.
Will also keep closely monitoring long-range models in order to
assess how long the heat wave will persist across the CWA, but at
the moment it's looking like aside from some minor cooling during
the middle of next week, this will be a prolonged event.Please be
mindful of both the heat and fire weather potential over the next
1 to 2 weeks as this even unfolds and avoid undo heat stress or
activities that may lead to wildfire starts.
&&
.AVIATION....as of 4:50 PM PDT Friday...VFR conditions through
Saturday with high level clouds. Weak seabreeze will keep winds
under 15 kt. Models suggest increasing mid level moisture late
Saturday afternoon.
Vicinity of KSFO...VFR. Northwest winds to 15 kt diminishing after
04Z.
SFO Bridge Approach...Similar to KSFO.
Monterey Bay Terminals...VFR.
&&
.CLIMATE...
Record High Temperatures expected with the upcoming heat event.
August 14 August 15 August 16
----------------------------------------------------------------
Santa Rosa 101, 2019; 103, 2019; 100, 2019;
Kentfield 100, 2019; 101, 2019; 101, 2015;
Napa 100, 2019; 102, 1906; 104, 2015;
Richmond 90, 2019; 91, 2019; 94, 2015;
Livermore 106, 1967; 108, 1967; 105, 1951;
San Francisco 86, 1995; 87, 1950; 90, 2015;
SFO 94, 2019; 94, 2019; 90, 2015;
Redwood City 100, 2019; 100, 2019; 101, 2015;
Half Moon Bay 74, 1965; 71, 1984; 72, 2015;
Oakland Dtown 90, 2019; 93, 2015; 92, 2015;
San Jose 98, 2019; 99, 2019; 97, 2015;
Gilroy 107, 1996; 104, 2019; 107, 2019;
Santa Cruz 96, 1906; 101, 2015; 94, 1983;
Salinas 84, 2019; 93, 2015; 94, 1933;
Monterey 86, 2019; 90, 2015; 83, 2015;
King City 102, 2019; 104, 1950; 103, 2015;
&&
.MARINE...as of 04:47 PM PDT Friday...Generally light to moderate
northwest winds will continue across the coastal waters through
the weekend as surface high pressure remains over the eastern
Pacific. Breezy afternoon and evening winds are expected along
coastal gaps, particularly down the Big Sur Coast south of Point
Sur. Winds will increase slightly over the waters early next week.
Mixed seas will persist with a short period northwest swell and a
couple of longer period southerly swells.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
.Tngt...Excessive Heat Warning...CAZ507-510-511-513-516>518
Heat Advisory...CAZ006-506-508-512-528>530
&&
PUBLIC FORECAST: Diaz
AVIATION: W Pi
MARINE: AS
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www.youtube.com/nwsbayareaThe San Francisco radar (KMUX), 46 km away, was scanning. The volume nearest the first event began at 18:13 UTC.
12 thunderstorm wind, 6 wildfire, 5 lightning, 2 excessive heat, 2 hail, 1 rip current, 1 dense smoke. Local standard time, as filed.
Heat wave prompts rolling blackouts across the Bay Area https://abc7news.com/bay-area-heat-wave-rolling-blackouts-california-power-outage-san-francisco/6372015/. Timing estimated.
Report of lightning striking a tree near San Ardo sparking a small fire.
Three teenagers were rescued in rough surf north of Sutro Baths and Ocean Beach in San Francisco https://www.sfgate.com/bayarea/article/Ocean-Beach-Sutro-Baths-surf-rescue-15487547.php. This occurred in the middle of a heat wave when a large number of people were headed to area beaches. SFFD reported 8 surf rescues that day.
Mesonet station on Old Coast Tower road.
Strong winds blow down multiple trees in lower Glen Arbor.
Mesonet station at Las Trancas.
Tree down blocking roadway near Gilroy.
Los Gatos station reported.
Observations in downtown San Francisco show multiple locations experiencing wind gusts over 50 mph.
Mesonet station at Shadowhawk reported wind gusts over 60 mph.
Mesonet site (PG&E) near Sausalito recorded gusts at 70 mph.
Altamont RAWS station reported gusts.
Spotter reported lightning struck a redwood tree shearing off about 20 feet of it this morning.
Mesonet station (PG&E) reported gusts near Forest Lake.
After multiple lightning strikes across the region and breezy erratic winds, approximately 20 separate fires broke out across counties (Santa Clara, Alameda, Contra Costa, San Joaquin, and Stanislaus) the morning of August 16th. These fires were later re-named the SCU Lightning Complex Fires https://www.fire.ca.gov/incidents/2020/8/18/scu-lightning-complex/. This complex became one of the top 5 largest fires in California State history prompting numerous evacuations, destroying nearly 400,000 acres and destroying over 200 structures. These fires resulted in 6 injuries (Civilian and Fire Personnel). The fires came dangerously close to the historic Lick Observatory on Mount Hamilton https://arstechnica.com/science/2020/08/a-california-wildfire-nearly-destroyed-the-historic-lick-observatory/. The fire was still burning at the end of August.
Lightning struck a utility pole in Palo Alto early Sunday morning causing a small fire and causing about 4,500 customers to lose power https://www.paloaltoonline.com/news/2020/08/16/storm-brings-fires-power-outages-to-the-bay-area.
Lightning struck a redwood tree in Redwood City https://sanfrancisco.cbslocal.com/2020/08/16/lightning-from-rare-bay-area-thunderstorm-leaves-damage-in-its-wake/.
Atlas Peak station reported.
On the morning of the 16th, lightning started multiple wildfires in Santa Cruz/San Mateo Counties that combined to form the CZU Lightning Complex https://www.fire.ca.gov/incidents/2020/8/16/czu-lightning-complex-including-warnella-fire/. At the end of August the fire had burned 84,640 acres, destroyed over 1100 buildings some of which were residential structures, injured three people (first responders), and killed another. Nearly 100,000 people were forced to evacuate. Historic Big Basin State Park sustained heavy damage from the fire burning down the parks headquarters. The fire was still actively burning at the end of August.
Lightning struck two houses in San Jose, setting one on fire https://sanfrancisco.cbslocal.com/2020/08/16/lightning-from-rare-bay-area-thunderstorm-leaves-damage-in-its-wake/. Amount of damage unknown.
Excessive heat across the region with widespread highs in the low 100s prompted 464 EMS calls across Santa Clara County.
Lightning sparked the River Fire in Monterey County on the afternoon of the 16th https://www.fire.ca.gov/incidents/2020/8/16/river-fire/. The fire burned over 48,000 acres destroyed 30 structures and damaged 13. Several evacuation orders were issued throughout the month and four people including fire personnel and civilians were injured. Both the River and Carmel Fires caused smoke and ash to rain down on surrounding cities. The fire was still burning at the end of August.
Spotter reported rain, lightning, and hail. Hail size estimated.
A second round of thunderstorms moved through the region into the morning of August 17th producing additional lightning strikes over the Bay Area. On the early morning of the 17th lightning produced a fire in Napa County that became the Hennessey Fire. Eventually, this fire merged with several other fires across Napa, Sonoma, Solano, Yolo, and Lake Counties (Gamble, 15-10, Spanish, Markley, 13-4, 11-16, Walbridge) to form the LNU Lightning Complex https://www.fire.ca.gov/incidents/2020/8/17/lnu-lightning-complex-includes-hennessey-gamble-15-10-spanish-markley-13-4-11-16-walbridge/. Over 350,000 acres burned with over 200 structures damaged and over 1400 destroyed along with 5 fatalities (3 in Napa County and 2 in Solano County) including civilian and fire personnel across all counties. The LNU Lightning Complex Fire is now one of the top 5 largest wildfires in California state history. The fire was still burning at the end of August.
Video on twitter showing small hail in Santa Rosa.
Mesonet station on Lake Drive reported.
A vegetation fire (Carmel Fire) broke out the afternoon of the 18th in Sky Ranch in Carmel Valley as a spot off the River Fire https://www.fire.ca.gov/incidents/2020/8/18/carmel-fire/. Multiple evacuations were ordered in the surrounding area with the fire ultimately destroying 73 structures and damaging 7. The combination of the Carmel and River fires rained down smoke and ash on surrounding cities. The fire was still burning at the end of August.
Lightning sparked the Woodward Fire in the Point Reyes National Seashore in Marin County https://inciweb.nwcg.gov/incident/7062/. The fire was first reported on August 18th in an area of dense vegetation that is sparsely populated. Evacuations were ordered for surrounding areas, and a video from the National Seashore Visitor Center recorded a small fire whirl in the midst of the fire https://bit.ly/2RZb95x. No structures were damaged or destroyed.
Smoke from multiple wildfires across California blanketed the Bay Area giving San Francisco the worst air quality in the world https://abc7news.com/smoke-forecast-bay-area-in-sf-today-air-pollution-wildfire/6377953/.
As the offices recorded each death: direct deaths were caused by the weather itself, indirect ones by something it set in motion.
| Event | Date | Age | Sex | Where | Kind |
|---|---|---|---|---|---|
| Wildfire, Santa Cruz Mountains | 2020-08-16 | 70 | Male | Unknown | Direct |
| Wildfire, North Bay Mountains | 2020-08-17 | 70 | Female | Permanent Home | Direct |
| Wildfire, North Bay Mountains | 2020-08-17 | Male | Permanent Home | Direct | |
| Wildfire, North Bay Mountains | 2020-08-17 | Male | Permanent Home | Direct |
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, August 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: 912918, 908484, 912921, 908507, 908489, 908515, 908488, 908514, 908490, 908505, 908506, 908504, 908481, 908517, 912890, 912905, 912900, 908509, 908492, 912901, 912906, 908494, 908483, 912887, 908485, 908511, 912892, 912897, 912922.