For homeowner and home buyers, one of the biggest rate-shopping difficulties is trying to respond to a market in flux.

On any given day, pricing is up and down, depending on the hour, and different lenders are coming in and out of competition.  The best priced bank in the morning, therefore, may not be the best priced bank in the afternoon.

And, choices get more complicated when you haven't settled on a particular loan product.  This is because mortgage rates change at a non-uniform pace across the product list.

For example, just because rates on 30-year fixed rate mortgages go up by a quarter-percent, it doesn't mean that rates on all loan products went up a quarter-percent.  Some may have increased by an eighth-percent.

Some may even have fallen.

It's why shopping for a mortgage rate and a mortgage product at the same time is like multi-variate calculus.

Except harder.

Consider the 15-year fixed rate mortgage as compared to its 30-year cousin.  At the beginning of the year, the interest rate differential was negligible.  Now, it's pronounced.

• December 2008: 0.250 percent difference in mortgage rate
• October 2009: 0.570 percent difference in mortgage rate

In December, there wasn't much reason to opt for the 15-year fixed over the 30-year.  Today, though, the 15-year fixed rate mortgage is a no-brainer for homeowner that don't mind its aggressive amortization schedule.   By Groundhog Day, though, who knows.

The same is true for 5-year ARMs.

Just 5 months ago, the 5-year ARM was priced worse than the 30-year fixed.  Today, it's about a half-percent better. If you happened to be holding onto to your Springtime Strategy, you'd end up in the wrong loan.

Therefore, homeowners planning for a new mortgage in 2010 would do well to leave their future mortgage strategy flexible. Until it's time to actually lock in a rate, don't etch the plan in stone.

Market dynamics tell us --  the math that works today probably won't work tomorrow.

For assistance with a rate locking strategy or comparing rates on loan products, call . I'll look at your situation and can make recommendations.

Dan Green is an active loan officer. Email or call 513-443-2020. Dan is on Twitter at @mortgagereports.