UPDATE 6:07 p.m.

Trained weather spotters and California Highway Patrol officers are reporting flash flooding from a thunderstorm in Pearblossom and Ctrystalaire (southeast of Pearblossom).

Water, mud and rocks are strewn across Highway 138. The National Weather Service warns that travel across the Antelope Valley along Highway 138 may be delayed due to flooding.

UPDATE 5:45 p.m.: Flash flood warning in effect for Pearblossom until 8:15 p.m.

The National Weather Service has issued a flash flood warning for Pearblossom and Crystalaire. At 5:13 p.m. the thunderstorm was located four miles southeast of Pearblossom, with rainfall rates of one to two inches per hour. Flooding is expected along Highways 2 and 138 (flash flooding has in fact occurred along Highway 138 in Pearblossom).

The NWS advisory notes that most flood deaths occur in automobiles. It cautions: “Never drive your vehicle into areas where the water covers the roadway. Flood waters are usually deeper than they appear. Just one foot of flowing water is powerful enough to sweep vehicles off the road. When encountering flooded roads, make the smart choice: Turn Around. Don’t Drown.”

UPDATE 5:30 p.m.

The storm is headed in a southwesterly direction toward the Santa Clarita and San Fernando valleys. Flash flooding is reported in the Highway 138 construction area in Pearblossom due to heavy rainfall. Eastbound traffic lanes are under water.

Also, a boulder is blocking traffic at Fort Tejon Road and Valyermo Road.

WARNING 4:46 p.m.

The National Weather Service has issued a severe thunderstorm warning for central-eastern Los Angeles County.

“This is a dangerous storm,” according to the alert, issued Sunday at 4:46 p.m. “The severe thunderstorm will cross over the Angeles Crest Highway in the Los Angeles County mountains within the next 10 minutes.”

The storm is capable of producing nickel-sized hail, lightning strikes, and winds in excess of 60 mph, according to the advisory.

The storm was spotted seven miles north of Falling Springs, which is in the middle of the Angeles National Forest area bounded by Newhall on the west, Pearblossom on the north and Pasadena on the south.

The NWS advises residents in the area to “prepare immediately for damaging winds, destructive hail, and deadly cloud-to-ground lighting. People outside should move to shelter, preferably inside a strong building but away from windows.”

7-DAY FORECAST for Santa Clarita

Tonight (Sunday) Partly cloudy, with a low around 69. South wind 10 to 15 mph decreasing to 5 to 10 mph after midnight. Winds could gust as high as 25 mph.

Monday – A 20 percent chance of showers and thunderstorms after 11am. Mostly sunny, with a high near 94. Light southeast wind becoming south southwest 10 to 15 mph in the afternoon. Winds could gust as high as 25 mph.

Monday Night – A 20 percent chance of showers and thunderstorms before 11pm. Partly cloudy, with a low around 59. South southwest wind 10 to 15 mph becoming light south after midnight. Winds could gust as high as 25 mph.

Tuesday – Mostly sunny, with a high near 90. Light south southeast wind becoming south southwest 10 to 15 mph in the afternoon.

Tuesday Night – Mostly clear, with a low around 61. South southwest wind 5 to 15 mph.

Wednesday – Sunny, with a high near 92.

Wednesday Night – Mostly clear, with a low around 61.

Thursday – Sunny and hot, with a high near 96.

Thursday Night – Mostly clear, with a low around 63.

Friday – Sunny and hot, with a high near 97.

Friday Night – Mostly clear, with a low around 65.

Saturday – Sunny and hot, with a high near 97.

Saturday Night – Mostly clear, with a low around 63.

Sunday –  Sunny, with a high near 95.