By Reginald Stanley. Posted March 7, 2024, 6:21 PM.

As the low pressure system responsible for our current storm departs the region, a shortwave trough is bringing heavy thunderstorm activity to parts of the region Thursday evening.

A passing shortwave, moving from northwest to southeast, began spawning intense thunderstorm activity over portions of the San Gabriel Mountains and San Fernando Valley in Los Angeles around 3:30 PM. Widespread thunder and lightning have been reported across these areas, with additional reports of hail and torrential rain. This prompted the National Weather Service to issue Flash Flood Warnings across the affected areas in Los Angeles County (mainly in the San Fernando Valley as well as communities along Interstate 210), as well as a Severe Thunderstorm Warning near La Verne where 60 MPH gusts were observed.

As the thunderstorm cells move into San Bernardino and Riverside counties Thursday evening, the National Weather Service has issued a Flash Flood Warning for a portion of southwestern San Bernardino County, including the cities of Rancho Cucamonga, Ontario and Upland - this warning is set to expire at 6:45 PM. A Special Weather Statement was issued for a portion of western Riverside County, including the cities of Riverside, Moreno Valley, Perris, and Beaumont - set to expire at 6:15 PM. This statement warns of gusty winds up to 40 MPH, heavy rain and possible pea-sized hail. In the WeatherCurrents network, stations from Riverside (Orangecrest) to East Hemet were reporting rainfall Thursday evening.