If you're headed over the hill to San Diego, be aware of nasty weather.

The National Weather Service has issued a Winter Weather Advisory for the mountains between the Imperial Valley and San Diego. The forecast calls for rain, fog, snow and winds through late Thursday night. Several inches of snow has fallen at Mt. Laguna with snow levels expected to drop to about 4,500. The forecast shows that another weather system will move into the region Friday and that will bring drier air.