The huge trunk and branches fell across both northbound lanes of the Saw Mill River Parkway late Sunday night.
Traffic was blocked for hours.
One southbound lane was closed as well.
No one was hurt, but drivers had a long wait while police redirected traffic and crews chopped up the tree.
In Connecticut, heavy rains are expected for a second straight day.
Flash flood watches are posted for southern Connecticut on Monday. A flood advisory has been issued for the northwestern part of the state, and a flood watch is up for the rest of Connecticut.
Anywhere from 2 to 11 inches of rain has fallen in the region since the weekend. Another 1 to 2 inches is expected Monday, with higher amounts possible in some areas.
Milford authorities say flooding made some roads impassable and water has flowed into businesses at the Westfield Connecticut Post Mall. Flooding problems are also reported in Naugatuck, Derby and Ansonia.
Route 34 in Derby was closed, and flooding was causing problems on Route 8 in Naugatuck.