Much of Northern California is in for another lightning scare this week, amid a summer of unusually frequent brushes with tropical moisture that creates the potential for lightning.
There is a higher likelihood of dry lightning late Thursday into Friday morning than in the previous lightning scares this summer, as meteorologist Daniel Swain of Weather West explains. The conditions are ripe for the kind of atmospheric instability that creates lightning, and there is only a slight chance of moisture, with less than a tenth of an inch of rain possible in some places.
"The models had looked pretty ho-hum regarding this week’s potential event until yesterday, but today’s runs are trending in a direction of substantially increased risk," Swain wrote on Tuesday. "In fact, today’s latest couple of model cycles are starting to depict what appears to be the classic set-up for an autumn lightning event in northern California."
And on Wednesday, Swain confirmed on Twitter that the model continues to show this strong potential for lightning.
"My thoughts from yesterday haven't changed much--in fact, confidence in some level of dry lightning has increased," he says, adding that the highest potential will be north of I-80. He adds that the lightning risk for the North Bay will be highest Thursday afternoon and evening, and the risk will shift more to the East Bay on Friday morning.
A Fire Weather Watch has officially been called for the North Bay from Thursday through 11 1.m. Friday.
Odds for elevated convection, and possible dry thunderstorms, appear to be increasing across central & northern CA for Thu into Fri period. Weak trough offshore will combine with subtropical moisture streaming northward to provide some risk of dry lightning. Attn: #CAfire #CAwx pic.twitter.com/8a1hvj1QbJ— Daniel Swain (@Weather_West) September 7, 2021
My thoughts from yesterday haven't changed much--in fact, confidence in some level of dry lightning has increased. Most activity will be from about I-80 northward, but some lightning is also possible across portions of Bay Area and western slopes of Central Sierra. #CAwx #CAfire https://t.co/7NivBbH6uE— Daniel Swain (@Weather_West) September 8, 2021
Swain still cautions that this could end up being just another scare, like the last two in July and August, but he says there is more likelihood for this lightning event to materialize.
"There is always 'bust potential' with dry lightning events in CA, and the two possible events earlier this summer did just that: they largely failed to materialize," Swain writes. "But this one has somewhat lower 'bust potential' than the earlier two, as in this case the weak low pressure system and mesoscale lift will provide a clearer focal point for triggering some elevated convection compared to the unstable but forcing-less non-events earlier this year."
And, he adds, conditions are pointing to "a dry environment favoring strong downdraft winds with any thunderstorms that develop — things could get dicey indeed on existing firelines."
The last thing anyone needs a repeat of the lightning event that happened on August 17 and 18 last year, which sparked wildfire complexes that scorched thousands of square miles across three zones of the Bay Area, destroying homes, killing people, and choking the region with smoke for well over a month.
As Jeff Lorber, a National Weather Service meteorologist, tells the Chronicle today, "Any lightning strikes pose significant hazards to our area because of very dry fuels, especially with the recent heat that we’ve been having and the very dry air mass that’s settled into place."
Photo: Leon Contreras