Rare August rainfall makes way for plummeting temps in Bay Area forecast

Remnants of moisture from former Tropical Storm Iselle brought a trace of rare rainfall to the Bay Area on Friday, paving the way for cooler temperatures throughout the week.

Read more OpenAI and Anthropic are ruining San Francisco

Roger Gass, a meteorologist for the National Weather Service’s Bay Area office, told SFGATE on Sunday that while the rain didn’t break any records, as much as five hundredths of an inch was recorded at Chews Ridge within the Los Padres National Forest, one of the highest peaks in Monterey County at over 5,000 feet. 

“August is typically our driest month of the year,” Gass said, “so it is rare but not unheard of to have rain showers and sprinkles.” 

The weather service issued a red flag warning for the Central Coast and the Santa Cruz Mountains to prepare for up to 15% chances of dry lightning, “which never materialized, thankfully,” he added. Since then, the moisture has shifted eastward, leading to sunny skies on Saturday and Sunday before the weather becomes significantly cooler. 

Gass said temperatures throughout the week are expected to be anywhere between five to 15 degrees below seasonal averages, driven by troughing — an elongated area of low pressure — off the West Coast and a marine layer that’s expected to deepen to 2,500 feet by Tuesday. Low clouds will continue to move inland throughout the coming days.

Read more Happy Face Killer’s eighth victim identified

Chances of rain could return by next week, but Gass said the weather service’s models are still in disagreement. Some suggest tropical moisture charting northward to the Bay Area, but others point to further troughing that would prevent it from moving and keep the region dry. 

“There’s fairly low confidence,” he said, “and we’re going to keep an eye on that Eastern Tropical Pacific due to active hurricane season.”