A thunderstorm in California. Photo via OnScene.TV.

Thunderstorms were building in the mountains around Idyllwild and parts of the Coachella Valley Thursday as monsoonal moisture drifted through the region.

The National Weather Service issued a Flash Flood Watch due to the instability. The watch is in effect from 2 p.m. into the overnight hours and encompasses the Anza Valley, Coachella, Idyllwild-Pine Cove, Palm Springs, the San Gorgonio Pass and surrounding locations.

As of 1:30 p.m., radar images showed bands of convective activity south of Anza and northwest of Desert Hot Springs. Most of the rain appeared to be along mountain slopes and ridges.

Precipitation amounts were not expected to be significant, but heavy downpours in short periods of time could trigger flash floods, according to the Weather Service.

The agency said that a “giant blob of air mass” emanating from a trough of low pressure stalled at the Arizona state line was churning up scattered storms.

“It looks pretty ominous on radar and satellite, but they should weaken,” according to an NWS statement.

Prognostication charts published by the Weather Service indicated that thunderstorms may linger into the weekend, but they will be concentrated in mountainous regions and the High Desert on Friday.

Another fetch of monsoonal moisture is forecast to arrive Sunday afternoon, generating convective instability into Tuesday. However, any potential rainfall will be east of the San Bernardino Mountains early next week, according to the charts.

High temperatures in the Coachella Valley were expected to exceed 100 degrees Thursday and Friday, with 105 possible through the weekend. Lows will generally hover in the mid-80s. In the Idyllwild-Pine Cove area, the highs will top out in the low 80s Thursday to Sunday, with lows in the upper 60s. In the San Gorgonio Pass, the mercury will push into the mid-90s Thursday to Sunday, with lows in the low 70s.

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