We have given back some of our gains (gains in Mortgage Backed Securities aka MBS which translate to lower rates) this morning due to positive economic news and negative inflation news. The Chicago PMI, which correlates to manufacturing sector strength and the Consumer Sentiment Index, which is a measure of how consumers feel toward the present and future economic conditions, both came in higher than analysts expected. In addition the Personal Consumption Expenditures(PCE), the Fed's preferred inflation indicator was slightly higher than their comfort zone. These events have caused some selling pressure in the fixed income markets, however the effects of the inflation data are mitigated due to the prevailing sentiment that current inflation readings are "trailing indicators"; the product of high commodity prices--now that commodity prices are declining, analysts are discounting current inflation data believing the commodity drop will give way to better future inflation readings.
All in all, MBS has done an admirable job of "standing it's ground" in the face of unfriendly data. At worst, your lender may require an additional .125 discount point today, but this will vary from lender to lender based on how they priced yesterday. Some lenders might actually improve due to "playing it safe" as they priced yesterday's gains into the rate sheets.
There's always a risk of volatility on days like today (market's closing early, friday before a vacation, near month-end). The events themselves are not the reason for the volatility, but more so, the fact that there are fewer market participants. The fewer the trades, the more impact each trade has.
No one could fault you for locking today as we are at near two month highs for MBS. And certainly, with so many "up" days in a row, we'll have to see some down days soon (possibly today). As often stated, floating when you should have locked hurts you much more then locking when you should have floated. Take your own risk tolerance into account, and remember, the shorter your time horizon, the wiser it is to lock. However, if you have a week or three to wait, several market factors suggest you'd almost certainly have at least the same, if not better, rate available to you at least one day in the next 3 weeks.
If you are "playing the market," don't forget about the instant updates that come out on the Professional version of the blog linked at the top of the page. You'll likely need to peruse the MBS primer (also at the top of the page), but ultimately, you should at least be able to glean appropriate warnings about reprice risk.