Flash Flood Watches Issued Across Mass.

With heavy rainfall and thunderstorms moving westward Thursday, the National Weather Service has issued flash flood watches across Massachusetts.

The watches are in effect for most of the state's counties from 4 p.m. Thursday through Friday morning, with the weather service forecasting sudden heavy downpours.

"Strong and gusty thunderstorms, vivid lightening, torrential rain, the outside chance of some hail, and I think the worst will be over probably by [Friday] morning," said meteorologist Mark Rosenthal.

"This may result in significant urban and poor-drainage flooding," the NWS said in its watch alert. "Small streams may also rise out of their banks."

The weather service adds that residents should monitor weather forecasts should flash flood warnings be issued. (A watch means that flooding is possible.)

Berkshire County is also under a tornado watch until 9 p.m. Thursday, and three western Massachusetts counties are under a severe thunderstorm watch until 11 p.m. Thursday.

Here are thunderstorm safety tips, from the Massachusetts Emergency Management Agency.