This fall has seen a ridiculously persistent ridge of high pressure — which has driven the majority of the Gulf of Alaska storms north of the Central Coast over the past six years — give way to a trough of low pressure along the West Coast. This condition has allowed a plume of subtropical moisture, or an atmospheric river, that stretched past the Hawaiian Islands to bring abundant rainfall to San Luis Obispo County during the first half of December. In fact, above-average rainfall has fallen throughout the Central Coast since October.