Mortgage rates held steady again today, keeping them in line with the lowest levels in more than 3 weeks.  They've also been uncommonly calm so far this week, which certainly isn't a bad thing when we're at 3-week lows.  The calm trend began showing cracks at the end of the day in terms of underlying bond markets (movement in bonds ultimately dictates movement in mortgage rates).

Bonds began to weaken in the afternoon.  "Weakness" in bonds corresponds to higher rates.  To put the move in context, bonds are still in better territory than they were on any day last week.  In other words, the weakness is quite modest for now. 

The risk is that it signifies some sort of shift because of bond trading behavior over the past 2 days.  To oversimplify a complex phenomenon, bonds (the ones we watch to get a bead on mortgage rate movement) hit the same roadblocks for 2 days in a row, and are in the early stages of moving back in a less friendly direction.  It could be a false alarm, but until they've reestablished a positive trend (i.e. making progress toward new rate lows), it makes more sense to play it safe in terms of locking vs floating.