The National Weather Service has issued a severe thunderstorm warning for Norristown and the surrounding area. Warning is in effect until 5:15pm, severe thunderstorm watch will expire at 10:00pm Sunday night.
This is issued when either a severe thunderstorm is indicated when a spotter reports a thunderstorm producing hail one inch or larger in diameter and/or winds equal or exceed 58 miles an hour; therefore, people in the affected area should seek safe shelter immediately. Severe thunderstorms can produce tornadoes with little or no advance warning. Lightning frequency is not a criteria for issuing a severe thunderstorm warning. They are usually issued for a duration of one hour. They can be issued without a Severe Thunderstorm Watch being already in effect.