The first thing to understand about mortgage rates over the past 3-4 weeks is that they haven't been moving nearly as quickly as the preceding months.  As such, "4 week highs" is a more dramatic designation than reality deserves, but it is nonetheless the reality.

Or at least it was the reality yesterday.  Today's rates were modestly lower, but again, we're dealing with a very narrow range overall and very small day to day movements.  The average borrower may not even see any change in their rate scenario since last week. 

The prospect for change is much greater tomorrow.  At the very least, the scheduled events have far more potential to cause bigger movement in either direction.  The event in question is the release of December's Consumer Price Index (CPI), a key inflation report with a consistent track record of market movement.

Economists and investors spend a significant amount of time and energy coming to a consensus on how the report is likely to come out.  As such, there's no legitimate way to predict whether the data will be good or bad for rates unless there's also a legitimate way to predict the future.

Last note: just because this report CAN cause a big reaction in rates doesn't mean it always WILL. The size of the reaction is generally proportionate to the size of the departure from the consensus.  Specifically, the most important number (Core month over month CPI) is expected to come in at 0.3%.  If it instead came in at 0.1%, that's a pretty big miss and one that would almost certainly push rates lower in a meaningful way.  Conversely, a result of 0.5% would likely send rates rapidly higher.