The improvements came on the heels of today's FOMC Announcement (Federal Open Market Committee or simply "The Fed") which surprised some market participants with it's inclusion of new verbiage describing how long the Fed anticipated that it would keep its "Fed Funds Rate" at so-called "exceptionally low levels." Until today, this verbiage read "through mid-2013," but is now changed to "through late-2014." Markets weren't necessarily expecting the inclusion of the word "late," and although mortgage rates would have likely improved with a simple mention of 2014, the "late" part added fuel to that fire.
While this indeed breaks the sideways trend at higher rates over the past 2 days, it's up to the rest of the week to solidify the rebound. In essence, markets will have an opportunity to respond to the eternal question: "is that your final answer." While the data through the end of the week doesn't possess the gravity of today's FOMC announcement, it could be enough to nudge the Best-Execution rate back to 4.0% depending on how it's received. In that sense, the risk posed by one singular event today is replaced by the risk posed by a group of events tomorrow and Friday. 3.875% is just barely back in the picture today, but it's too soon to say whether or not the past two days at 4.0% were the exception to a long-term trend, or the beginning of a new one.