During the day on May 29th, a warm front lifted northward across western Massachusetts. Although the day began cloudy, some breaks of sun started to occur by early afternoon. At the same time, a potent upper level disturbance over Ontario started to approach the region and a strong jet streak was located just to the north. With a moist southerly flow moving into the region at the surface, it became rather humid as well.
With all these ingredients coming together, thunderstorms developed across upstate New York by mid afternoon and began to spread eastward. The thunderstorms reached Berkshire County by the evening hours. Many of the thunderstorms organized into a strong squall line, producing wind damage. These thunderstorms produced a significant amount of lightning, as well, which in combination with the wind damage, led to some power outages across the area.
With the region already rather saturated from repeated thunderstorms over the past week, the additional heavy rainfall that occurred caused flash flooding in some areas. This caused roads to be closed due to being impassable by flowing water. Portions of Williamstown were hit quite hard, as at least eight roads were damaged due to flooding. Two homes were without road access as a result of the flooding.
Thunderstorms pushed east of the area by around midnight, ending the threat of severe weather.