Cooler conditions with showers and thunderstorm chances today. Breezy northerly winds will follow Monday into Tuesday. Additional mountain shower chances midweek.
Discussion
Latest radar scans show showers along the northwestern California coastline. Weather stations across interior northern California are currently reporting that temperature observations are trending approximately 2 to 10 degrees cooler than this time yesterday morning, valid at 230 AM PDT.
Cooler temperature are expected today. Daytime highs are expected to reach the 60s to mid 70s for the Valley, upper 50s to around 70 for the foothills, and mid 40s to mid 60s for the mountains. These temperatures will be trending below normal for mid to late October climatology.
A weather system will bring scattered shower and thunderstorm chances to the area today. Precipitation will first arrive along the Coastal Range and the west side of the Valley this morning and spread inland through the day. Storm total precipitation amounts of 0.05″ to 0.75″ in the Valley, and 0.20″ to 0.80″ in the foothills and mountains are forecast.
The National Blend of Models (NBM) suggests generally a 15 to 35 percent probability of thunderstorm development this afternoon for much of the Sacramento Valley, and Sierra foothills/mountains. Model soundings suggest CAPE values of 100 to 500 J/kg this afternoon, and anomalous CAPE is highlighted on the Extreme Forecast Index (EFI) for today. Potential impacts with any thunderstorms that develop include dangerous lightning, gusty winds, small hail, and brief heavy rain.
Rain rates are expected to remain below debris flow criteria, however there could be brief heavy rain with any thunderstorms that develop near the August Complex, Caldor West, Mosquito and Dixie West burn scars this afternoon and evening.
Drivers who encounter rain or slick roads should slow down, use wipers/headlights, and drive with caution.
After the passage of this system, breezy north to east flow will develop behind it. Wind gusts around 20 to 25 mph, locally up to 30 mph, will be possible on Monday, with the strongest winds out of the north direction along the western portion of the Sacramento Valley. No fire weather concerns are expected.
Gusty winds may create difficult driving conditions for high profile vehicles, and cause loose objects such as decorations to blow around. Wind speeds look to taper off later Monday night into Tuesday.
Temperatures will also be trending slightly warmer on Monday and Tuesday, compared to today. A continued influence of troughing may allow for the potential for additional shower chances late Tuesday into Wednesday, with the best chances over the mountains, although confidence in maintaining this pattern is still low to medium for this timeframe.
Extended Discussion (Thursday through Sunday)
Clusters and ensembles have come into better agreement with broad trough pattern over Northern CA in the extended as energy drops down from the north. This will bring cool temperatures and periods of unsettled conditions, especially over the mountains. At this point, dry conditions look to prevail on Thursday.
By late week, the NBM advertises a 15-30% chance of precipitation over the mountains and the northern Sacramento Valley. Although blended guidance still shows some spread, high temperatures appear to remain below normal throughout the extended period with Valley highs in the mid 60s to low 70s. Stay tuned for updates.