Thunderstorms and possible hail jolt parts of LA County as flash flood warning is issued

Thunderstorms jolted parts of northern L.A. County from an otherwise sunny day Thursday, with claps of thunder, lightning, brief showers and even the possibility of hail.

The National Weather Service earlier warned that showers would develop over the mountains and drift south over the valleys, bringing with them the chance of small hail, lightning and "localized heavy rain," which could cause minor debris flows or flash flooding in some areas.

Then in the afternoon, a flash flood warning was issued for the San Fernando Valley through 6 p.m. after more significant thunderstorms developed over the region. Such warnings are issued when a flash flood is coming or in progress, according to the NWS.

Keep in mind that flash floods are sudden and violent floods that can start within minutes. Weather experts advise that if you’re in an area that’s likely to flood, you should head uphill quickly.

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For the avid weather follower, NWS announcements follow a specific format to convey flash flood information. Here’s what it includes:

• Hazard type: The specific type of event.
• Source information: How the weather event was determined (e.g. radar, emergency managers, gauges).
• Impact potential: The risks that could happen. For example, a flash flood could be life-threatening and widespread.
• Tags: How extreme the damage could be, how it was identified and any other events connected to the flood (e.g. rainfall or dam issues).

What to expect next

Gusts of wind in some areas could also hit 50 mph.

The chance of showers was expected to extend into tonight. Rain totals for most areas should range between 0.5 and 0.75 inches of rain. There's a very low chance of minor or shallow debris flows over recent burn areas, according to the National Weather Service.

Snow levels are expected to stay above 4,000 feet, with the possibility of up to 1 inch of snow in the Tejon Pass.