For the first time this week, we'll get economic data in the morning that actually stands a chance to move markets.  In fact, the only 2 reports of the week (strictly speaking about "scheduled economic data") that even stand a chance of mattering are both today.  Top that off with the afternoon that hosts the last of the week's Treasury auctions with 30yr Bonds at 1pm and Thursday's a contender for the most meaningful day of the week so far.  This isn't so much about Thursday being awesome as it is about the rest of the week being uneventful.

On an MBS-specific note, keep in mind that tonight is "the roll"--our shorthand way of referring to "Notification/48-hour Day for Class A MBS"--and so prices of May coupons will be replaced by prices of June coupons after the close, making it SEEM as if MBS have suddenly dropped (when in fact we're simply shifting our field of vision to the next bucket of MBS--one that hasn't fallen off the assembly line yet.

Additional refresher on Settlement:  

Class A refers to Fannie/Freddie 30yr Fixed MBS

"48 Hour Day" refers to the day on which any account that is selling or swapping MBS this month, must exchange the "pool information" (all the vital stats of the loans comprising the pools that will fill a trade; stuff like the weighted average interest rate of the pool, average loan size, credit score, loan age, etc..), and is so named because this exchange of information is required to occur 48 hours before the actual settlement date (when it falls on a Thursday, settlement is the following Monday, however).  

Oversimplified, it's like a swap meet where buyers and sellers can inspect each others' goods, confirm the price, and take some time to make sure everything's in order before exchanging cash for goods, or simply trade goods for goods.