Current MBS Price and Day Over Day Change:

FN 5.5 30YR MBS = 101-21  .... +1-06 (36 ticks)

This is off quite a bit from the highs of the morning which were over 102, but is a very nominal 38% retracement.  Lenders that priced between 9:00 and 9:30 might reprice for the worse if they priced in gains aggressively, but that is unlikely.  We will either encounter overhead resistance around the 100-22 to 100-26 level and come back down, in which case, locking makes sense, or we may break through and continue to rally above 102.

Either way, try to gauge how much your rates changed from yesterday to today.  If you are getting a majority of the gains priced in, that's when looking at locking makes more sense.