Hail Storm - April 16, 2018

A spring storm system swept through the Bay Area bringing wild weather that included: copious amounts of small hail, gusty wind, higher elevation snow and scattered thunderstorms.

A cold upper level low pressure system originating off the British Columbia Coast moved southward and ultimately pivoted across California. As the colder air aloft moved over the Bay Area it helped to destabilize the atmosphere. Below is one computer model depicting the passing cold air aloft and increased instability at the surface. (See NAM forecast animation ). The model forecast was ultimately verified by the Oakland balloon sounding, which showed a CAPE 402 J/kg. Showers developed on April 15, but increased in coverage and intensity on April 16, as the cold core moved overhead. See the regional radar loop below showing widely scattered showers and thunderstorms passing through the much of Northern California. One of the more notable storm cells popped up in San Francisco Bay and tracked eastward into the Oakland Hills area. See the local radar loop below showing the storm cell passing into the Oakland Hills area. Given the low freezing levels near 4,000 feet it's not too much of a surprise that a developed cell like this one could produce ample hail. Numerous reports from the media and on social media indicated that this hail covered the ground making driving dangerous. The NWS office in Monterey received hail reports through out the entire day ranging from pea size to dime size. To alert the general public and agency partners Significant Weather Advisories were issued to highlight stronger storm cells. (see example below)Lots of hail pictures are posted below. Snow was also reported in the Santa Cruz Mountains and the East Bay Hills. The Ham Cam on Mount Hamilton showed a Winter Wonderland at the Lick Observatory.