The atmospheric river is causing hazardous driving conditions in Berkeley, CA, particularly on steep and winding roads and major highways like I-80. The heavy rain and coastal fog are reducing visibility and increasing the likelihood of hydroplaning, posing risks to commuters and residents. While the city itself may not experience severe winter weather, those traveling to higher elevations, such as the Sierra Nevada, should be prepared for potentially snowy conditions. Drivers should remain vigilant and adjust their driving habits to ensure safety.