Some of the most damaging and deadly fires in California history have been caused by PG&E power lines, including several fires this season.
Red flag warnings have been hoisted for parts of the Bay Area, along with a large region to the north and east, including Redding and Chico, because of northeasterly winds that could gust up to 60 mph in some locations, along with very dry air.
The offshore winds are the result of a storm system moving into the Southwest United States, which is bringing beneficial rains and mountain snows to Southern California, Arizona and New Mexico but only brief showers and even a thunderstorm to parts of Northern California. It did not produce the substantial rains needed to end the region’s fire season.
“As offshore really takes hold through the day the airmass will continue to dry. Gusty offshore flow and dry conditions will keep critical fire weather conditions in place over the North and East Bay higher terrain,” stated the National Weather Service forecast office in San Francisco in a forecast discussion posted on its website. As of early this morning, winds were already gusting above 50 mph in higher terrain north of San Francisco, the NWS said.
The critical fire weather conditions in Northern California will last into the early part of Thursday, the NWS predicted. “Stay tuned — fire season is definitely not over yet until the region receives widespread wetting rainfall.”
California saw an onslaught of severe fire weather conditions in October, with an unusually high number of offshore wind events in Northern California, along with 10 days of offshore Santa Ana winds in Southern California, six of which were rated as moderate to strong, which was above average for the month.
The October wind events and late start to the rainy season in Northern California have dried out vegetation, with an index that measures how hot a fire will burn showing extraordinarily high levels — above the 97th percentile, in parts of the region. This includes the San Francisco Bay area and Sacramento Valley.
Offshore wind events are more numerous during the fall and winter months, but because of winter rains, the fire risk in December through the end of the rainy season tends to be minimal. However, in a trend that some studies show is in part related to human-caused climate change, the typical fire season may be shifting and expanding, with a later start to the rainy season becoming more common.
Climate change is also influencing California wildfire seasons by making the dry season hotter, which dries out vegetation faster and more significantly.