The unusually steamy weather that has afflicted San Diego County this week will be for at least one more day, and thunderstorms could drench the inland valleys on Wednesday, National Weather Service forecasters say.
Streams of warm, wet air from the east have created local moisture levels never seen this early in July. Phil Gonsalves, a forecaster for the weather service, said the precipitable water level, which is a measure of the amount of water vapor in the air, was higher than has ever been recorded in San Diego on July 10.
Although most of that moisture is high in the atmosphere, the humidity levels at the surface are still very high for San Diego.
“That’s why it’s been so uncomfortable,” Gonsalves said. “For us, it’s rare, which is why it’s so nice to live in San Diego.”
High temperatures should be near 80 at the coast through Friday, while the inland valleys hit the high 80s and low 90s. The desert should be in the low 100s, and the mountains should be in the mid 70s.
Some spots in North County got a good soaking on Tuesday morning. Vista recorded 0.19 of an inch of rain, and Oceanside had 0.08. Temecula, in Riverside County, had 0.20. Lightning strikes were also detected about 40 miles off the coast.
On Monday night, thunderstorms over the desert to the east of the county collapsed, sending the remaining clouds over San Diego County. Those clouds helped shield the region and keep the overnight temperatures high. Gonsalves said the clouds should stick around most of Tuesday, and that should also keep the afternoon temperatures down a few degrees.
Gonsalves said that if more thunderstorms form on Tuesday, they should be over the mountains and desert later in the afternoon, and areas west of the mountains should remain dry. That’s the normal summer pattern, and if storms do drift west of the mountains, they are usually weakened.
Wednesday could be a different story. Moisture levels should remain very high, and there’s a 20 to 30 percent chance that storms will develop over the inland valleys, Gonsalves said. If the storms do form there, most likely in the afternoon, heavy rainfall rates could create the possibility of localized flooding, he said.
After Wednesday, thunderstorms should be confined to the mountains and desert, Gonsalves said. The weather service expects limited thunderstorm activity Friday and Saturday, but another influx of moisture early next week could fire up another round of storms over the mountains an desert.