A slightly deeper marine layer tonight will bring dense fog to Orange County’s coast and the coastal plains. The higher coastal terrain and inland to the western portions of the San Diego County valleys will also be shrouded. Fog is expected to begin forming late this evening and last through 9AM Tuesday. Visibilities will fall below 1/4 of a mile at times. Use caution when driving as visibility can diminish rapidly with little to no warning and please remember to use the low beams.