Wednesday evening forecast – Oct. 20
Mostly benign weather through the week, warming through Thursday then cooling through Saturday. Very light rain possible around San Luis Obispo County today and Friday. A storm system will bring widespread moderate to heavy rain later Sunday and Monday, with minor flooding, gusty winds, and cooler conditions. Potential for debris flows in recent burn scars, including Alisal fire burn scar. Warming and drying expected Tuesday and Wednesday.
An upper level trough, currently pushing into the coast north of Eureka, is streaming a plume of moist southwest flow over San Luis Obispo County and northward. A few showers could result through tonight over San Luis Obispo County with any amounts very light and under 0.10 inches. Otherwise, the rest of the area could see a few upper level clouds from this and nothing else.
Thursday is the warmest day of the week with highs along the coast in the 60s to 70s and inland spots into the upper 70s.
Friday another trough will pass on through bringing a chance of light rain for San Luis Obispo County. To the south, there is a better chance of low clouds and fog developing, but still not a sure thing. Gusty northwest winds will develop Friday night behind the trough. The weekend will be cooler.
We are keeping a close eye on our first significant storm of this rain season. A cold front will form south of the low off the Gulf of Alaska, and likely stall for about 24 hours somewhere over the northern half of California. This stalled plume of moisture and steady rain is now looking more likely to stay north of San Luis Obispo County, which has pulled some of their projected rain totals down a little. So while our area will see less of an Atmospheric River, a healthy cold front is still on target to move through southwest California sometime between late Sunday night and Monday Evening, first for San Luis Obispo County and last through Ventura County. Amounts between 1 and 3 inches is still the best estimate for San Luis Obispo and Santa Barbara Counties, with 0.50 to 1.50 for Ventura County. The highest totals will be over the south and southwest facing mountains and foothills. Rain rates should generally stay in the 0.25 to 0.50 inch per hour range, with isolated rates slightly higher. As such, not expecting significant debris flows outside of the fresh Alisal burn scar which could see road impacting flows. Thunderstorms are unlikely, as well as significant snow as snow levels stay above 8,000 feet. There will be some gusty southwest winds around the frontal passage, especially over the mountains. While the majority of the rain should end by late Monday Night, some showers could linger into Tuesday. Expecting warming and drying conditions otherwise Tuesday and especially Wednesday when locally breezy offshore flow may form.
