Our upper low is heading eastward, allowing for a nice Wednesday evening. With onshore flow, the marine layer will fill in a little better overnight in coastal areas, and could reach a few valley areas. Skies will clear slowly, but it should be mostly sunny by the afternoon, if not earlier.
On Thursday, our ridge of high pressure will flatten out, and a gradual cooldown will begin. Low temperatures will be in the 40s to low 50s. Highs will be in the mid to upper 60s, with a few interior valleys straggling in the low 70s. It will still be slightly above normal in most cases.
A large upper low will reach the eastern Pacific Ocean by Friday, with a broad trough extending southward. More mid and high-level clouds will drift across our region, in addition to a deep marine layer. Temperatures will decrease by another couple of degrees. Late Friday, there is a chance of light rain in San Luis Obispo County.
The front will move over our region on Saturday, bringing a 20 to 40 percent chance of light rain. There will be a second period of rain on Sunday. In total, preliminary models estimate at up to a quarter inch of rain for most areas, and up to a half inch for northwest SLO County. Snow levels will fall to around 4,500 feet.