With temperatures getting getting down to Angostura levels on Tuesday (because they'll be so bitter), the MBTA is warning us to watch out for possible delays, even as they get crews ready to make sure trains and switches are at the ready:
The MBTA will make every effort to operate subway trains and buses at or near regular weekday schedules, but some delays may occur. ...
The MBTA is implementing its cold-weather mitigation measures, which include storing buses and trains indoors overnight, and conducting regular checks of vehicles that remain outside. The MBTA will be cycling train sets in and out of rail yards so they are not sitting idle for extended periods of time. For trains that are not running throughout the system, MBTA teams will be opening and closing doors as well as testing brakes and propulsion systems for any moisture buildup and freezing. Signaling and track crews will be inspecting all rights-of-ways to ensure that heaters for track switches and third rail are performing as designed.
So check the T winter-weather page before you leave.