Mortgage rates are dropping this morning on weaker-than-expected Retail Sales data from December. Lower rates means more bang for your home-buying buck.

Excluding motor vehicles and parts, December’s “ex-auto” sales receipts were down roughly $500 million from November. Analysts had expected receipts to grow.

The relevance of Retail Sales to home affordability isn’t obvious, but it’s definitely logical.

Retail Sales is directly related to consumer spending and consumer spending accounts for the majority of the U.S. economy. When consumer spending slows, the economy often does, too. It leads investors to seek out “safe” investments.

It’s the reason why stock markets often drop on weak economic data — stocks are among the riskiest investment classes available.

Conversely, the best place to find safety is in the market of government-backed bonds.  This world includes products like U.S. Treasuries and many of the mortgage-backed bonds that help set mortgage rates for people in Cincinnati.  Weak economic data puts mortgage bonds in demand.

For rate shopper, this is good news.  More demand for mortgage bonds causes mortgage rates to fall.  Mortgage rates are lower this morning because Wall Street is shedding some risk.

December’s Retail Sales report closes out a year of generally-weak data.  2009 marks just the second time that Retail Sales fell year-over-year since the government started tracking it 40 years ago.  The other year was 2008.

For home buyers in Hill Valley and around the country, though, today may represent an opportune time to lock a mortgage rate.  Housing data is still improving and other economic indicators are showing strength.  Soon, Wall Street will shift from a “safe” mentality and move toward risk.

When it does, mortgage rates will rise.