Actually it is done in IMC. Not in Low Vis but yes down to CAT I limits.
A. The arriving aircraft is on final approach.
B. The arriving aircraft is radar identified. The departing aircraft has commenced its take-off roll when the arriving aircraft is not less than 2 miles from the threshold of the landing runway provided:
a. separation will increase to a minimum of 3 miles within 1 minute after takeoff;
b. the tower is equipped with a display upon which radar track data, including
aircraft ground speed, is being displayed.
c. radar procedures are established for the release of successive IFR departures; and;
d. airport controllers are trained and certified to apply the procedure;