The Pending Home Sales Index moved higher in March as home sales were spurred by low mortgage rates and an expiring tax credit.

A “pending home” is a property that is under contract to sell, but not yet closed.

March marks the second straight month in which the Pending Home Sales Index improved after a series of weak showings this past winter.

March showed a 5 percent increase over the month, but the Pending Home Sales Index is still off its October 2009′s peak. October 2009 is a comparable period to March 2010 in that it marked the 1-month deadline before the home buyer tax credit’s initial expiration date. The credit was later extended to April 2010, of course.

That said, March’s surge in sales is being felt on the street.

Home buyers no doubt noticed the change in activity. Around the country, anecdotally, multiple offer situations were more common last month and “right-priced” homes tended to go under contract quickly.

The increase in March’s Pending Home Sales is diminishing the nation’s home supply which, in turn, should cause prices to rise in most markets.

Today’s buyers should consider making an offer sooner rather than later. Looking at the data, it appears the best time to have found a “deal” on a home may have been in February.

For the first time this year, Fannie Mae announced significant updates to its mortgage underwriting guidelines.

The changes include newer, harsher ARM qualification standards, the elimination of a once-popular loan product, and tighter rules for interest only mortgages.

Fannie Mae made its official announcement April 30, 2010. The changes will roll out to home buyers and homeowners over the next 12 weeks.

The first guideline change is tied to ARMs of 5 years or less.

Mortgage applicants must now qualify based on a mortgage rate 2% higher than their note rate. For example, if your mortgage rate is 5 percent, for qualification purposes, your rate would be 7 percent.

The elevated qualification payment will disqualify borrowers whose debt-to-income levels are borderline.

The second change is Fannie Mae’s elimination of the standard 7-year balloon mortgage. Balloon mortgages were popular early last decade. Lately, few borrowers have chosen them, though. Mostly because rates have been relative high as compared to a comparable 7-year ARM.

And, lastly, Fannie Mae is changing its interest only mortgages guidelines.

Effective June 19, 2010, Fannie Mae interest only mortgages must meet the following criteria:

1. The home must be a 1-unit property
2. The home must be a primary residence, or vacation home
3. The borrower’s FICO must be 720 or higher
4. The mortgage must be a purchase, or rate-and-term refinance. No “cash out” allowed.

Furthermore, borrowers using interest only mortgages must show two full years of mortgage payments “in the bank” at the time of closing.

Earlier this year, Fannie Mae-sister Freddie Mac announced that as of September 2010, it will stop offering interest only loans altogether.

Between Fannie Mae, Freddie Mac, the FHA, and other government-supported entities, the U.S. government now backs 96.5% of the U.S. mortgage market. So long as mortgage default rates are high, expect approvals for all borrower types to continue to toughen.

Mortgage markets improved last week on tame inflation data, a benign statement from the Federal Reserve, and ongoing credit problems in Greece.

The factors combined to drop conforming mortgage rates to their lowest levels in 6 weeks.

It’s an unexpected development considering that mortgage rates were supposed to rise post March 31, 2010. That was the day the Fed’s support for mortgage markets ended.

Since then, however, a month-long string of devastating economic and meteorological events within the Eurozone sparked a global flight-to-quality that benefited “safe” assets such as mortgage bonds.

May 2010 may not be so kind.

The week starts with news that Greece reached a $147 billion bailout agreement with the IMF Sunday. This is a plus for the Eurozone and mortgage market negative. Rates should rise on the bailout.

Also on Monday, the government releases Personal Consumptions and Expenditures data.

PCE is the Fed’s preferred inflation gauge and it’s expected to show an annual read of 1.3 percent. Anything higher and rates should rise.

Then, for the rest of the week, employment data takes center stage.

• Wednesday : ADP releases its private sector employment data
• Thursday : The government releases initial jobless claims
• Friday : The government releases April’s job report

Jobs are key to the U.S. economic recovery, tied to consumer spending, consumer confidence, and mortgage delinquencies. If job growth is better than expected, mortgage rates should rise. If job growth is worse, rates should fall.

There’s no “best day” to lock this week so keep an eye on the market. However, if rates rise as quickly in May as they fell in April, you won’t have much time to act.

Earlier this week, Standard & Poors released its February Case-Shiller Index, a home price tracker for select metropolitan areas.

Overwhelmingly, home values fell in the 20 markets tracked by the Case-Shiller. Only San Diego showed a modest increase. The other 19 markets averaged a 1.23 percent decline between January and February.

However, that’s not the story you read in the most papers. Instead, headlines read that home values were up in the United States, citing annualized data.

Unfortunately for active home buyers and sellers, year-over-year data isn’t all that helpful when making a real estate decisions. It’s the month-to-month data that matters. Month-to-month changes in home prices are what defines a housing market. Month-to-month is what sets the tone for contracts and negotiations on a purchase.

The rosier, annualized data published this past week just doesn’t capture the reality of what was the February 2010 market. And even then, the data is somewhat useless because it’s from February and May will be upon us next week.

Case-Shiller is on a 2-month lag — hardly reflective of the “right now” of real estate.

When you’re looking for real estate data that actionable, consider using sources that are more “real-time”. A real estate agent may be the right place to start. Because for all the data that Case-Shiller and the other housing indices collect, it can never be as relevant to your individual needs as a well-executed, timely market analysis.