Thunderstorms - Photo courtesy of Johannes Plenio on Unsplash

Severe thunderstorm warnings expired in Riverside County, the National Weather Service reported Thursday, but rain and lightning strikes are expected to continue throughout the day.

Thunderstorm cells dumped heavy rain Wednesday in parts of the San Bernardino National Forest and caused roadway flooding in the San Gorgonio Pass and east of the Coachella Valley, while lightning strikes caused damage in at least one location, amid the first monsoonal activity of summer.

The storm prompted the NWS to issue a severe thunderstorm warning, but it expired at 6 p.m. Wednesday. The storm weakened below severe limits and did not pose a threat to life or property. Periods of moderate rain, lightning and gusty winds were expected to continue in the area Thursday.

According to the California Highway Patrol, one lane on Interstate 10 in the San Gorgonio Pass became impassable after a downpour shortly before 3 p.m.

Additional flooding occurred on Highway 177 in the Eagle Mountain area, just north of Desert Center, according to the CHP. Hail was also reported there.

About 3 p.m., lightning charred a utility pole in the area of Highway 74 and Lake Hemet Road in Anza, according to the Riverside County Fire Department.

It was unknown whether the strike triggered a power outage.

No fires were reported in connection with the storm cells.

Doppler radar images for the area showed intense cells rolling south to north through the wilderness at the south end of the San Bernardino National Forest, over the eastern Coachella Valley.

The cells were expected to shed some of their energy and begin dissipating at nightfall.

Meteorologists said high humidity and elevated temperatures, influenced by a fetch of moisture pushing into Southern California from Mexico, generated conditions ripe for convective-driven instability.

“By Wednesday afternoon, monsoonal moisture will be fully in place, with surface mass convergence,” according to an NWS statement. “This looks to provide the best opportunity of thunderstorms to develop. Most cells will produce .25 to .50 inches.”

Prognostication charts published by the NWS showed dueling high- and low-pressure systems over Southern California on Wednesday afternoon, with the possibility of scattered thunderstorms in most of Riverside and San Bernardino counties.

“There may be just enough moisture remaining Thursday to allow for isolated showers or thunderstorms to develop over the mountains … before dry weather returns Friday and into the upcoming weekend,” the agency stated.

In the Riverside metropolitan area, the swelter will continue for the rest of the week, with highs generally in the mid- to upper-90s and lows in the mid- to upper-60s.

Triple-digit heat will remain the norm in the Coachella Valley, with the mercury topping out between 105 and 110 degrees going into the weekend, while overnight temps won’t fall much below 80. In the Temecula Valley, peak temperatures are expected to hover in the upper 80s to low 90s, with lows falling to around 60 this week, according to the NWS.

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