Mortgage rates have been on a tear recently, moving sideways with reckless abandon.  Since the middle of February, the "effective rate" (based on actual rate sheet offerings and upfront costs) has held inside a narrow range of 4.52% and 4.58%.  This lies in stark contrast to the persistent move higher during the first month and a half of 2018 which saw the same effective rate rise from roughly 4.0% into the 4.5% range. 

When rates are as flat as they are on the approach to a key market event like this Wednesday's Fed announcement.  We often see a break in that narrow range after the key event.  For now, there's no reason to believe Wednesday WON'T be such a day this time around.  Even if Wednesday turns out to be a dud in terms of its impact on rates, it's always safest to plan for the risk (or opportunity) of a sharper move in rates for better or worse.