Not simply because MBS are currently at the same price levels as Friday afternoon do we say that their week begins tomorrow.  In fact, Friday's levels aren't really a factor in that statement.  It's really been the entire past two days of sideways action around long term pivot points as well as 10yr yields asymptotic approach to their epic 2.10 pivot during the same time, that combine to give the impression that bond markets are heavily anticipating tomorrow's FOMC festivities ("festivities" = first ever forecast release, announcement, and press conference).  Nothing ground-breaking has occurred in terms of levels for either side of the market yesterday or today, and the absence of economic data simply exacerbates the sideways drive.  Here's the most recent alert from MBS Live to bring you up to speed on the day:

The earlier round of selling leading up to and away from the Fed's twist buying took production MBS to the edge of 101-19, which is both a long and short term pivot point. Since then, they've mostly drifted sideways and slightly higher, easing some earlier reprice risk. But keep in mind that the range remains narrow and we're not very far from levels that would reintroduce reprice risk. MBS and Treasuries are both sort of drifting aimlessly sideways, in what seems like perpetual "wait-and-see" mode ahead of tomorrow's FOMC announcement, forecasts, 5yr auction, and perhaps even tonight's State of The Union (it's somewhat conceivable that a government initiative could be announced that would have an effect on MBS. That's a stretch though).

regarding 101-19 as a pivot point, here's some more context:

I dressed up the TSY chart a bit more, with my take on the big-picture sideways themes that pertain to 2.10.  Yes yes yes... We didn't quite get there yesterday, only 2.094, but in the longer term, as we've previously discussed, we're not always going to land perfectly on pivot points.  So "2.10" can be tought of as "2.10 or thereabouts," say, plus or minus a few bps.  With that in mind, the following chart is basically saying that 2.10 was first suggested as an important pivot point at the very beginning of the rally.  There was the initial pull back and most of the month of October that pivoted back above the line, but other than that, it's most been uncrossed.  In late September/early October, we saw 2 instances of 1.82 acting as a major pivot point at the outer limits.  Recent Dec/Jan lows roughly revisited those levels, making for a nice big sideways trend with lots of ceiling and floor bounces around the midpoints (1.93-1.98, affectionately referred to as "1.95").

In short, 10's have been casually and uneventfully playing around below 2.10, and have returned to the edge of that playground for further instructions.  Either they'll get to keep playing, or be asked to come inside, and MBS will likely take their directional cues tomorrow from whatever Treasuries do with the 2.10 level UNLESS there is something MBS-specific from the Fed, in which case, performances could vary (in fact, we'd rather get away from trying to predict what will happen tomorrow and simply leave it at this: things are sideways... They've backed up to longer term technical levels, and tomorrow seems like the focal point.  Such focal points more often than not, result in a more pronounced break in one direction or another, but there are plenty of examples of them turning out to be "duds" as well.  So we're with the markets on this one: watching and waiting.