453.1750 with PL 167.9 in New Haven is linked with 155.9550 (DPL 143) and 853.4125 (DPL 445). The linked repeaters were intended to be use as inter-agency interoperability system for New Haven and the town immediately surrounding it as part of the "Urban Area Security Initiative (UASI)". Just about everything I have heard on it is New Haven PD surveillance ops. I did hear some testing from New Haven FD some time back. Based on the test traffic, 853.4125 was Ch. 3 in the NHFD radios with talkaround on Ch. 6.
Most of the parade related activity will be on 460.150 but I would certainly listen to Yale PD and the regular New Haven PD channels. While it's possible that they would use the UASI channels, it's unlikely. Doesn't hurt to have them in the scan list though.
Make sure you check and see if the parade is still being held tomorrow. There might be a chance that it will be canceled, despite the rain or shine policy. Check the local news sites after 8am in case it is canceled.
Keep it programed in, for the most part its not used but any special event detail utilizes it Yale games, Yale events, fireworks etc... other towns use it but it has over the years unofficially taken over by NHPD.