After a slight but steady rise in recent weeks, mortgage rates turned downward this week, dramatically boosting the volume of refinancings, according to Freddie Mac's (FRE) Primary Mortgage Market Survey released Thursday. 30-year fixed-rate mortgages averaged 5.16 percent with an average 0.7 point, dropping below last week's 5.26 percent average. Last year at this time, the 30-year fixed-rate mortgage average sat significantly higher at 5.72 percent. “Interest rates for 30-year fixed-rate mortgages are almost 1.5 percentage points below 2008’s peak set on July 24, 2008, offering many homeowners an incentive to refinance,” said Frank Nothaft, Freddie Mac vice president and chief economist.  “This would translate into a monthly payment savings of around $188 on a $200,000 mortgage." 15-year fixed rate mortgages dropped as well,  averaging a mere 4.81 percent this week, down even farther than last week's 4.92 percent average, and well below the year ago reading of 5.25 percent. Five-year Treasury-indexed ARMs were no exception, falling from 5.26 percent last week to 5.23 percent this week. The average on One-year Treasury-indexed ARMs was the lone climber, averaging 4.94 percent, up from last week when it averaged 4.92 percent. But the overall drop in mortgage rates sent refis surging, just as it has in recent months. “The Bureau of Economic Analysis estimated that the weighted average mortgage rate of loans outstanding was about 6.2 percent in the fourth quarter of 2008," Nothaft said. "As a result, the share of refinancing among the total number of conventional mortgage applications has exceeded 50 percent for the past 11 weeks and averaged 80 percent over this period, according to the Mortgage Bankers Association.” In similar findings, Bankrate.com's weekly mortgage rate survey reported the 30-year fixed-rate benchmark fell 36 basis points to 5.34 percent, while the 15-year fixed-rate benchmark fell 28 basis points to 5.03 percent. Bankrate's analysis said the drop in rates occurred Tuesday afternoon, soon after Treasury Secretary Tim Giethner unveiled an overview of the new financial rescue plan. "Investors apparently wanted to hear specifics," said Bankrate's Holden Lewis. "When Geithner didn't provide specifics, investors sold stocks and bought bonds. Yields went down, and so did mortgage rates." Write to Kelly Curran at kelly.curran@housingwire.com. Disclosure: The author held no relevant investment positions when this story was published. Indirect holdings may exist via mutual fund investments. HW reporters and writers follow a strict disclosure policy, the first in the mortgage trade.