The first significant storm of winter will drop heavy rain across much of San Diego County from roughly 9 p.m. to midnight Thursday and produce showers Friday, temporarily easing the threat of wildfires but doing comparatively little to lift precipitation to seasonal levels, the National Weather Service said.
The region will be hit by the brunt of an atmospheric river — a column of moisture out of the west that will flow into north coastal San Diego County before spreading to the backcountry and then sliding into downtown San Diego.
Much of the region is already wet from the showers and drizzle that have fallen since late Tuesday. About 3 inches of precipitation had drenched Palomar Mountain through noon Thursday. But forecasters said the incoming system is not likely to cause the San Diego River to rapidly rise and overflow its banks.
However, Thursday night’s finale could become heavy enough in some areas to cause flash flooding, especially in the Palomar Mountain area, which could get as much as 4 inches of rain. And sporadic lightning could occur in the backcountry.
Either way, seasonal rainfall totals will remain way below normal, and forecasters say next week will be dry and sunny.
San Diego International Airport generally averages 5.76 inches of precipitation from Oct. 1 through Feb. 13 — but this season, it had gotten only 0.86 inches through noon Thursday. The incoming storm could add 0.75 inches, but the city would still have a large deficit.
Ramona also is faring poorly. It averages 8.24 inches of rain during that period but had only recorded 1.77 inches through noon Thursday. The figure could rise about 1 inch overnight.
Forecasters say the the small amount of rain the county got this week and about a week ago is producing green shoots of vegetation in the backcountry. But those could quickly wither if long-term conditions remain fairly dry.
