San Francisco reached 46 degrees on Monday morning when a cold breeze from western Canada penetrated the region, the National Weather Service said. Conditions are expected to cool even further from Monday night to Tuesday morning.

“Downtown SF has the potential to drop below 40 degrees on Tuesday morning,” wrote the weather service on Twitter. “The last day this happened was January 6, 2017 (minimum temperature was 39). #CAwx.”

With the cold air moving in, snow depths around the Bay Area could drop to as much as 300 meters inland by early Tuesday and as much as 250 to 150 meters in the valleys of the North Bay.

Could we see snow in San Francisco?

“I think there are parts of the Bay Area that have the potential for a few snowstorms to hit the surface, but in places along the bay like San Francisco that seems very unlikely,” said Roger Gass, a forecaster for the weather service.

It snowed an inch to two inches on the streets of San Francisco on February 5, 1976, pollinating the Marin Headlands, north of the Golden Gate Bridge.

Kunst Frisch / Hearst

Snow has fallen and stuck on the ground 11 times in San Francisco, according to records dating back to the gold rush. During a recent cold snap on February 5, 2019, a weather observer spotted snow on the Twin Peaks, but it did not stick and was not one of the 11 on February 5, 1976 when Twin Peaks iced up to 5 inches. This event was well photographed and pictures show people all over town throwing snowballs and building snowmen.

February 5, 1887 was reputedly the snowiest day for the city at 3.7 inches on record at the National Weather Service’s office in the Financial District of San Francisco. The top of the twin peaks is matted up to seven inches. In fact, it did snow a couple of times on February 5th, making it the snowiest day of the year in SF history.

Snow fell only twice in December. On December 31, 1882, it was a staggering 3.5 inches and snow fell from 11:30 a.m. to 4:20 p.m. Less than an inch was recorded on December 11, 1932.

The National Weather Service shared a map showing where snow might fall in the SF Bay Area in the coming days.

NWS

While snow is unlikely in San Francisco on Tuesday, fresh powder is expected in other areas of the Bay Area. The weather service has shared a map showing where snow is likely to fall (see map above).

The official snow forecast from the Meteorological Service said, “Snow depths will generally be between 1,500 and 3,000 feet this week. The exception is Tuesday morning, when we expect the coldest air at altitude and snow depths will be significantly lower, you will see snow depths of up to 250-500 ft above North Bay on Tuesday morning. That means the potential for a rain-snow mix could reach some of the North Bay Valley locations [region] will have snow depths of up to 1000-2000 ft on Tuesday morning. “

Given the cold temperatures in the mix, Gass noted that people should look for family members and neighbors who don’t have adequate sources of heat.

“Make sure you protect sensitive plants and animals outdoors,” warned the weather service. “Also note that roads that are wet in the early hours of the morning can become icy in places if we step into this colder pattern.”

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The hottest temperature on Earth ever recorded may have been reached on Sunday afternoon, as the mercury in California’s Death Valley hit 130 degrees.  

The temperature was reached at 3.41pm Pacific time on Sunday, according to the National Weather Service. 

If verified, the reading would break Death Valley’s previous August record by three degrees, the Weather Service tweeted. In a follow up tweet the World Meteorological Organization (WMO) said it will verify the temperature.

‘Everything I’ve seen so far indicates that is a legitimate observation,’ said Randy Cerveny, who leads the World Meteorological Organization’s weather and climate extremes team. 

Scroll down for video  

Visitors posted the record online; the visitor center thermometer runs 3-4 degrees warmer

Tourists visiting the California park posted series of photos of the barren landscape

Death Valley is famed for being the hottest place on Earth, and on Sunday did not disappoint

Fires raging close to houses in Salinas, California, last night – around 260 miles west of Death Valley

Fires raging close to houses in Salinas, California, last night – around 260 miles west of Death Valley

Trees and bushes burning in Salinas, California, last night – around 260 miles west of Death Valley

In an email to The Washington Post, he wrote: ‘I am recommending that the World Meteorological Organization preliminarily accept the observation. 

‘In the upcoming weeks, we will, of course, be examining it in detail, along with the U.S. National Climate Extremes Committee, using one of our international evaluation teams.’ 

Death Valley currently holds the record for the hottest temperature ever recorded on Earth – a record set on July 10, 1913, of 134 degrees.

Yet experts for years have believed that the reading was not accurate.

An extensive analysis of that record conducted in 2016 by Christopher Burt, an expert on extreme weather data, concluded it was ‘essentially not possible from a meteorological perspective.’ 

The remains of a home in Salinas that was destroyed by wild fires last night

A chimney block stands naked against the horizon after a home was destroyed by flames in Salinas, west of Death Valley, in California

Experts believe that Sunday’s temperature was the hottest ever accurately recorded

A 131F reading from Kebili, Tunisia, set on July 7, 1931, also has ‘serious credibility issues,’ according to Burt. 

Many believe that a 129F readings recorded in Death Valley on June 30, 2013, and in Kuwait and Pakistan in 2016 and 2017, were the highest ever reliably measured on the planet. 

If only those readings are considered, then Sunday’s 130-degree temperature would unseat them as the highest measured.  

Death Valley is the lowest, driest and hottest location in the United States. 

Furnace Creek, where its temperature is measured, sits at 190 feet below sea level in the Mojave Desert of southeastern California.  

In July 2018, its average temperature of 108.1F represented the hottest month ever measured on the planet. During that month, it hit at least 120 degrees on 21 days. 

Typically, such blazing heat records happen in July — the Northern Hemisphere’s hottest month — which makes Sunday’s 130F reading stand out.

Heavy smoke near Salinas, California, blotted out the sun on Sunday as wildfires raged

Wildfires swept across Contra Costa County in California on Sunday, sparked by lightning

Firefighters battled to put out the blazes on Sunday, inland from San Francisco

The roasting temperature came as a heat wave continues to grip much of the western United States.

More than 80 million people were under heat alerts Friday from the Central and Southern Plains as well as for nearly the entire West Coast.  

Oakland, California, on Friday hit 100F for the first time on record in August, while Phoenix tied its highest temperature for the month: 117F.

On Saturday, Needles, in California’s southeastern desert, soared to 123 degrees, its highest August temperature on record.

Sacramento hit 112F on Sunday, topping its previous August record of 110F. 

The hot weather overwhelmed the state’s electrical grid, prompting the California Independent System Operator (ISO), which runs the grid, to warn of an electricity supply shortage on Sunday evening.

California ISO sought to buy additional power to avert another rolling outage and issued a Flex Alert, urging utility customers to conserve energy during the late afternoon and evening hours.

The heat wave across the western United States is expected to last until Wednesday

Blackouts hit a large swathe of California on Friday evening from 6.30-10pm

Forecasters warned of ‘stifling heat’ across a large part of the western United States

‘It’s going to be tight,’ said Severin Borenstein, a board member of the ISO and energy economist at the University of California, Berkeley.

‘There is a real concern that they would have to do it again tomorrow and Tuesday,’ he said Sunday about the rolling outages.

California ISO ordered the first rolling outages in nearly 20 years on Friday when it directed utilities around the state to shed their power loads. 

The state’s three biggest utilities — Pacific Gas & Electric, Southern California Edison and San Diego Gas and Electric — turned off power to more than 410,000 homes and businesses for about an hour at a time until the emergency declaration ended 3 1/2 hours later.

The ISO instituted a second, but shorter, rolling outage Saturday evening that cut power to more than 200,000 customers.

The power grid is mostly stressed during the late afternoon and early evening because of higher demand and solar energy production falling after the sun sets.

California increasingly relies on energy from renewable sources instead of natural gas-fired plants. During the summer months, the state imports power when demand goes up, but a heat wave sweeping Western states meant there was less available, Borenstein said.

‘They are literally calling as well as emailing and saying, “Do you have any power to sell us to everyone in the West,”‘ he said. ‘But they can’t force the other areas to sell their electricity when those other areas need it for themselves.’

La Jolla beach near San Diego was packed on Saturday as people sought respire from heat

Baker Beach, beneath San Francisco’s Golden Gate Bridge, was a popular destination Saturday

Kayakers in La Jolla hoped to cool off on Saturday amid searing, record-breaking heat

The last time the state ordered rolling outages was during an energy crisis in 2001. Blackouts occurred several times from January to May, including one that affected more than 1.5 million customers. 

The cause was a combination of energy shortages and market manipulation by energy wholesalers, infamously including Enron Corp, that drove up prices by withholding supplies.

The heat sent Californians to outdoor spaces and waterways, even as officials worried about the risk of increased coronavirus transmission. The state reported another 77 deaths Sunday, bringing total deaths in California from the virus above 11,200.

Unsettling weather also triggered an unusual warning by the weather service of a fire-induced tornado at an out-of-control forest fire that broke out north of Lake Tahoe on Saturday afternoon.

A massive fire cloud known as a pyrocumulonimbus formed over the fire, which started east of the town of Loyalton, about 40 miles west of Reno, Nevada. 

When high winds collided with the fire and whipped it into the air, a spectacular tornado-shaped spiral of flames was formed.

The fire has burned at least 45 square miles and triggered evacuation orders for sparsely populated communities along State Route 395 by the California-Nevada border, said Tahoe National Forest spokesman Joe Flannery.

Firefighters aided by water-dropping helicopters and air tankers faced ‘extreme fire behavior,’ he said, and worked through the night to extinguish spot fires and protect threatened structures.

At one point, the fast-moving fire jumped a highway and came dangerously close to a fire truck. A fire crew from Truckee tweeted a video of firefighters dragging hoses as they ran alongside a moving truck that was dodging the flames.

Ryan Peel said firefighters created some defensive space around his slot machine distribution warehouse in Chilcoot, but he was worried the erratic winds could still put his business in the line of fire.

‘Yesterday was extremely emotional, as we were at the mercy of the wind and the unpredictability of the fire,’ Peel said. ‘I was stressed and terrified at the idea of losing everything I’ve spent my life working for.’

With zero containment and strong winds in the forecast, he said, ‘we are not out of the woods yet’.

On Sunday, a rare summer thunderstorm brought lightning (pictured over Healdsburg, California, on Sunday) that sparked several small blazes in Northern California and stoked a huge wildfire that has forced hundreds of people from their homes north of Los Angeles

Lightning illuminates the sky over the eastern span of the Bay Bridge as a storm passed through San Francisco on Sunday morning

More than 4,500 buildings remained threatened by the fire burning toward thick, dry brush in the Angeles National Forest. Firefighters already battling the blaze in steep, rugged terrain with scorching heat faced more hurdles when hundreds of lightning strikes (pictured over San Francisco) and winds up to 15mph pushed the flames uphill

On Sunday, a rare summer thunderstorm brought lightning that sparked several small blazes in Northern California and stoked a huge wildfire that has forced hundreds of people from their homes north of Los Angeles.

More than 4,500 buildings remained threatened by the fire burning toward thick, dry brush in the Angeles National Forest. 

Firefighters already battling the blaze in steep, rugged terrain with scorching heat faced more hurdles when hundreds of lightning strikes and winds up to 15mph pushed the flames uphill.

‘We set up a containment line at the top of the hills so the fire doesn’t spill over to the other side and cause it to spread, but it was obviously difficult given the erratic wind and some other conditions,’ said fire spokesman Jake Miller.

The Lake Fire was just 12 per cent contained Sunday and has burned nearly 28 square miles of brush and trees. Fire officials said 33 buildings had been destroyed, including at least a dozen homes.

Temperatures reached more than 110 degrees and a pyrocumulus created erratic fire behavior, fire spokesman Tom Ewald said.

Thunderstorm and excessive heat were also a concern for firefighters battling a blaze that blackened almost 4 square miles in the foothills above the Los Angeles suburb of Azusa. 

The fire, believed to be started Thursday by a homeless man, is only 3 per cent contained.

Due to the triple-digit temperatures throughout the weekend and the combination of prolonged heat and smoke from wildfires, ozone pollution reached levels not seen in a decade in some areas. 

Air quality may reach unhealthy to very unhealthy levels in several regions of Southern California on Sunday and Monday afternoons, the South Coast Air Quality Management District said.

In Northern California, moisture from an offshore tropical storm fueled a thunderstorm that brought nonstop lightning strikes early Sunday, some of which ignited small fires and knocked out power across the San Francisco Bay Area.

Wind gusts reached 75mph according to the NWS, which said another round of lightning may develop early Monday.

‘This is probably the most widespread and violent summer thunderstorm event in memory for Bay Area, & it’s also one of the hottest nights in years,’ tweeted Daniel Swain, a climate scientist at the University of California, Los Angeles.

Scientists have found that the intensity, duration and frequency of heat waves worldwide are increasing due to human-caused climate change. 

A 2019 study found the planet has entered a ‘new climate regime’ with ‘extraordinary’ heat waves that global warming is worsening. 

Dallas, Houston, Phoenix, Las Vegas, Los Angeles, Portland and Seattle are among the cities under heat alerts.

For the West, an excessive heat warning is in effect until Wednesday for parts of Arizona, California and Nevada, with high temperatures expected to reach 110-125 degrees. 

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Temperatures in the Bay Area spiked Tuesday and provided t-shirt weather in the winter. Most of the places in the area, including San Francisco, were by 3pm in the ’70s

Santa Rosa Airport reached 80 degrees at 2 p.m., the highest temperature recorded at this location so far this year. The average first 80 degrees in Santa Rosa is around March 15, according to the National Weather Service.

For comparison: Phoenix and Las Vegas – places in the west that often experience warm weather in winter – still have to reach 80 in 2020.

The reason for this mild weather in mid-February? Rowe stated that temperatures usually cool off overnight, but last night an offshore pattern of north to northeast winds blowing from inland valleys to the coast never allowed this to happen.

“Last night we still had a little offshore wind at just 2,000 feet above the surface,” Rowe said. “That limited the nocturnal radiation, that is the radiation that the earth emits overnight. It has not cooled down.”

This wind setting is worrying in the fall at the height of the fire season, but Rowe said we had enough rain in November and December to wet the soil and vegetation and prevent extreme drought conditions that could start wildfires.

ALSO: Why planes that landed on SFO flew scary near Highway 101 on Sunday

Wednesday marks the start of a cooling trend as a dry, cool system from the north sweeps the area. Temperatures on Wednesday afternoon will be 5 to 10 degrees lower than on Tuesday afternoon.

The weather is dry until February and there is still no chance of significant rain. The southern edge of a storm that hits the Pacific Northwest can bring sprinkles to the North Bay from Saturday night through Sunday morning, but the likelihood is slim.

“That was an issue all year,” said Rowe. “Your umbrellas to the northwest have been used well in storm after storm and we are at the end of those storms.”

Amy Graff is a digital editor at SFGATE. Email her: araff@sfgate.com.

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