You may hear talk of "big changes" to the forecast after Thanksgiving. It will get colder, yes. However, the change in airmass does not appear to be lengthy in duration although the colder shot will be noticeable for many.
In the days leading up to Thanksgiving, the temperature tend will moderate slowly. We could hit 60 on one or two days next week in the city and points south, with Thanksgiving one of the best potential candidates for that...but even if that doesn't happen it will be a few degrees milder over the coming days. Computer modeling suggests a cold front slices through the region on Black Friday, bringing an end to the mildness that will be in control over the next several afternoons and giving the latter half of Thanksgiving weekend a chilled ending.
Temperatures on Saturday and Sunday probably don't get out of the 40's for highs. It won't be terrible...it won't be arctic cold. It will be below average and remind us we're quickly sliding into the coldest weeks of the year. However, the shot of chill will be quick in duration in all likelihood as a stronger storm system begins to organize in the West for the beginning of the week after Thanksgiving, which will travel east for the middle and latter half of that week. As of now, that bigger storm looks like rain but it does look like a storm that will reinforce a below average temperature regime from November over the East for the beginning of December.