Last night was Class A Settlement for MBS--aka "the roll."  If the roll causes any confusion (pretty normal), try thinking of it like an assembly line.  Every box on the assembly line is like every month of the year.  As the boxes roll down the line, MBS sellers fill the boxes with loans, and eventually the box at the front of the line runs out of room.  When this happens,  any remaining loans required to fill the box (whatever the seller committed to the buyer) are put in the box and the box is closed.  It falls off the line and secondary market participants shift their focus to the next box that's about to run out of conveyor belt space and the cycle repeats.

"MBS Prices" almost anywhere you find them, will be referring to the "lead box" on that assembly line--the first box in line to be sent out the door.  The prices assigned to the subsequent boxes on the assembly line are incrementally lower each time you move further down the line (October is cheaper than September is cheaper than August, because buyers will pay more for identical MBS today vs a month from today, all other things being equal).  When the lead box falls off the line, "MBS Prices" are now referring to the new lead box, which is simply the next box in line.  That box was priced roughly .375 lower for months, so "MBS Prices" look as if they've dropped .375 immediately because they've switched their representative box from the one falling off the line to the new 'lead box.'

If none of that made sense, I spent a night in the desert with a generator, laptop, and powerpoint to bring you the following crude, peyote-induced animation of this assembly line metaphor that I tend to lean on when it comes time to talk about the roll.   (prices and gaps between delivery months are totally arbitrary):

Nothing about today's calendar is any more interesting than the roll or last minute homemade powerpoint animations.  That said, Wholesale Inventories reports at 10am.  It's not a market mover and anything that actually steps up as a market mover today will likely not have been on the schedule or otherwise expected.  Here's a look at the real-world effects of the roll.  That sharp move down at the end is simply the shift of our collective gaze toward the next box on the assembly line.