WP - Dry Season At Mt. Shasta 3 Weeks Longer Than In 1979; In San Francisco, 2 Weeks Longer

[hatrack]

EDIT

Modern research suggests that California’s wet season isn’t necessarily drying out, but it is becoming more compressed. Atmospheric scientists point to a tendency for winter rains to arrive later and later, rather than ramping up around mid-fall, with fewer heavy rain events during the fall fringe season. The biggest events are most concentrated in December and January, precipitation more compactly squeezing into the heart of the wet season.

To evaluate changes in the wet season, we probed the average first and last dates of heavy rainfall, or calendar days with a half-inch or more of precipitation bookending the wet season. We also looked at the number of days with a half-inch or more of rainfall during the cool/wet season, as well as the amount of rain to come down each fall.

What we found

We first discovered that the dry season is getting longer — especially in Northern California. Northern California traditionally has a more pronounced wet vs. dry season because it is in a better position to intercept winter storms that dive southeast surfing the jet stream. We defined the wet season as the window between a winter’s first and last rainstorm with a half-inch or more in a calendar day.

Our findings showed that at Mount Shasta in Northern California, the dry season has grown 22 days just since 1979. In Redding, the dry season is a bit shorter but sticks around later — during the peak of wildfire season. San Francisco saw its dry season expand by 14 days, while Sacramento has to wait more than three weeks longer for the wet season to arrive. Farther south, such places as Bakersfield saw a growth of its dry season, but it was a toss-up in San Diego and Fresno. That’s unsurprising, since the transitions between dry and wet seasons are more blurred in Southern California. What matters is that the autumn wet season is arriving later in San Diego and Fresno, heightening wildfire risk.

EDIT

https://www.washingtonpost.com/weather/2021/05/02/california-wildfire-season-growing/

[CentralMass]

1. We have had a very det spring in Oregon. It doesn't bode well for the fire season.