Low pressure spinning off coast of California was the culprit on Monday.
Fresno spiked 110 degrees on Monday, the hottest day of the year. It broke a 121-year-old record and surprised a lot of folks who had seen forecasts of about 100.
What happened? It was sunnier than expected in the morning, and the San Joaquin Valley got a wind-blown taste of the southwest desert. Then the lightning and thunder show started in the evening.
The culprit was low pressure spinning in a counterclockwise direction in the Pacific Ocean, said meteorologist Paul Iniguez of the National Weather Service in Hanford.
“The counterclockwise spin brought a flow of air up from the desert,” he said. “It was hotter in the Valley than many desert locations. In eastern Kern County desert, the temperatures were in the 90s.”
Meteorologists call this kind of low pressure a “cutoff low,” because it is separated from the jet stream — the high elevation blast of wind coming across the Pacific eastward into the West Coast.
Without the jet stream to move it along, the low could sit in one place and spin winds into California.
The high temperature in Fresno was reported at 109, but it actually climbed to 110 after 5 p.m., Iniguez said.
The flow of air coming from the east continued into the evening and thunderstorms began to appear. There were power outages and fires. In Kern County, there were 1,600 lightning strikes, Iniguez said.
“There were probably more people who saw lightning than people who saw rain,” Iniguez said. “I wouldn’t call this weather unusual in August, but it’s not typical.”
Probably the most unique story so far: a giant sequoia that caught fire in June 2012 and continued right through the winter. It’s amazing because Sierra winters can be brutally cold and wet at 7,000 feet where this tree lives.
The San Joaquin Valley’s notorious dirty air has been worse on other years, but it has exceeded the federal ozone standard 10 of the last 11 days.
Yosemite Falls, which usually begins dwindling in early July, is almost dry. If you look around other Sierra web cams, you’ll see a very dry watershed.
Pine Flat Reservoir in Fresno County is down to 30% of capacity. San Luis Reservoir in western Merced County is at 20%. With most of July and all of August still ahead, farmers and small towns may get the worst of this summer.
Meteorologist Steve Johnson, a private consultant in the Fresno area, posted a list of California records set on warm Wednesday this week.
It was topped by Fresno’s 85 degrees, which broke the 2007 record for the day by one degree. Burbank broke its record by eight degrees.
From reading the list, it looks like 2007 was pretty warm, too. But there are also some very old records that were broken. The Riverside record was more than a century old.
Here’s the list, which includes the place, the new record and the old record:
Fresno, 85° (84° set in 2007), South Lake Tahoe, 69° (64° set in 2007), Burbank, 93° (85° set in 1951), Sandberg, 77° (76° set in 2007), Woodland Hills, 94° (92° set in 2007), Ramona, 86° (84° set in 2007), Riverside, 95° (90° set in 1902), Thermal, 97° (96° set in 1997), Alpine, 84° (81° set in 1994), El Cajon, 86° (81° set in 2004), Elsinore, 92° (88° set in 1926), Escondido, 87° (86° set in 1951).
If warm weather continues, the snowpack in the Sierra Nevada will come rolling down a little sooner than usual. The snowpack is about 60% of average right now — better than last year when it was about 45% as spring began in late March.