The National Weather Service has issued a severe thunderstorm watch alert for every county in Connecticut. The alert for New London, New Haven, Middlesex and Fairfield counties is effective from 3:17 to 9 p.m. Wednesday.

NWS defines a severe thunderstorm as one that produces hail with a diameter of at least one inch and/or winds that are at least 58 miles per hour. The agency encourages people to be prepared to move to a safe place if threatening weather approaches.

In a forecast discussion, NWS said the main threat will be "damaging winds, frequent lightning and heavy rain," and that localized flooding can't be ruled out but the overall duration of heavy rainfall is in question.

NWS said a watch "is used when the risk of a hazardous weather or hydrologic event has increased significantly, but its occurrence, location, and/or timing is still uncertain." This is less urgent than a warning, which was issued for Tolland County for 2:46 to 3:30 p.m.