The Bay Area is under a slight risk of flash flooding today as heavy rainfall from an approaching West Coast cyclone is anticipated. There is a 15% chance of excessive rainfall, which could be intensified by local atmospheric instability. Residents are urged to stay alert, particularly in urban areas known for flooding, and to avoid unnecessary travel. The danger extends into the nearby upslope regions of the Sierra Nevada, where heavier rainfall may increase runoff and create dangerous conditions. It is essential to take preparedness measures to ensure safety.