First-ever Tornado Warning issued for San Francisco as strong atmospheric river hits California
San Francisco experienced its first-ever Tornado Warning on Saturday morning, December 14, 2024, as a strong atmospheric river swept through the region with heavy rain and strong winds.
Satellite image of strong atmospheric river impacting California on December 14, 2024. Credit: NOAA/GOES-West, RAMMB/CIRA, The Watchers
San Francisco experienced its first-ever Tornado Warning on Saturday morning as a strong atmospheric river (AR) brought heavy rain and strong winds to the region.
The National Weather Service (NWS) issued the warning for northern San Mateo County and parts of downtown San Francisco shortly before 05:51 local time (LT). According to the NWS, a cyclonic signature on the radar displayed sufficient rotation to justify the warning.
The warning ended at 06:07 LT as the storm moved northeast of downtown San Francisco. The warning for the remainder of the area expired at 06:20 LT. A special alert for a potential waterspout over San Francisco Bay near the Bay Bridge expired 10 minutes after the tornado warning.
Although the strongest part of the storm system has passed, isolated severe thunderstorms remain possible in parts of the Bay Area through the morning, according to the NWS.
According to the Center of Western Weather and Water Extremes (CW3E), this AR was expected to make landfall with moderate to strong AR conditions and re-intensify briefly south of the Bay Area.
The NWS Weather Prediction Center (WPC) has issued a slight risk (≥ 15%; level 2 of 4) excessive rainfall outlook (ERO) over the Northern California Coast Ranges, including the Russian River watershed. A
marginal risk (≥ 5%; level 1 of 4) ERO has been issued for the Sacramento Valley and Northern Sierra Nevada foothills.
Twelve stream gages in California are forecast to rise above the action/monitor stage, and two stream gages are forecast to rise above the minor flood stage. The California–Nevada River Forecast Center is showing a 59% probability that the Russian River at Hopland will exceed the minor flood stage.
Compared to the November AR event, snow levels are expected to be lower during this storm. At least 30 to 90 cm (1 – 3 feet) of snow are forecast in the higher terrain of the Klamath Mountains, Southern Cascades, and Northern and Central Sierra Nevada.
Winter Storm Warnings have been issued for these areas, with major-to-extreme winter storm impacts expected.
References:
1 Quick Look at Atmospheric River Impacting California – CW3E – December 13, 2024
2 Tornado warning shocks San Francisco residents during intense storm – CBS – December 14, 2024
Rishav is a skilled researcher specializing in extreme and severe weather reporting. He combines exceptional research capabilities with scientific precision to deliver clear, data-driven articles. Known for uncovering critical information, Rishav ensures his work is accurate, insightful, and impactful. His passion for both science and literature fuels his dedication to producing high-quality news articles. You can reach him at rishav(at)watchers(.)news.
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