Everyone knows the housing market is slowing; the question is how fast and how painfully.

It's not an easy question to answer, especially since, like politics, all real estate is local. Economists and journalists may talk in national numbers, but those can look very different from neighborhood statistics. Even during the housing boom, for example, some locales felt nary a nudge upward in home prices.

But we can pinpoint places that have slowed rapidly, where home prices may still even be increasing but at a dramatically different pace than before. And, surprise: They aren't necessarily areas with struggling economies, where prices have already dropped over the past year.

Ann Arbor, Mich., a city stung by thousands of auto-industry layoffs, rates as the worst performing real estate market between the second quarter of 2005 and the second quarter of 2006, according to data from the Office of Federal Housing Enterprise Oversight. Ann Arbor suffered a 1.2% decline in median home value over that span, compared with a 3.7% gain nationally.

That sounds less than promising. But a peek at some metro areas where prices have held up well over the past year -- in most cases surpassing the national average -- shows a troubling trend. There have been rapid decelerations in price growth from the go-go market of the prior few years, a tip-off that the next year is likely to bring outright reductions in home values to these boom towns.
 
"There are the chronically weak markets like Detroit, and then there are those that have been strong but where the psychology is changing," says Lehman Bros. economist Ethan Harris.

Many such markets, such as Reno, Nev., and Barnstable, Mass., on Cape Cod, are driven by seasonal, second-home buyers, often the first to head for the sidelines during a slump.

To identify some of the most dramatically slowing metro areas in the United States, we turned to data from the Office of Federal Housing Enterprise Oversight. We averaged out the annual price change for each location from 2002 through 2005. Current median prices for single-family homes were obtained from the National Association of Realtors and, in a few cases, local sources.

For instance, home price growth in Barnstable dropped to 4.9% over the past year from an annual average of 14.4% over the previous four years, a difference of 9.5%. Reno's numbers are similar, slowing to 8.8% growth this past year from 17.8% annually between 2002 and 2005.
 
"All resort markets should be dropping faster than primary markets; it's not a necessary purchase," says David Lereah, an economist with the National Association of Realtors. 

Lereah predicts that third-quarter housing numbers, due out in November, will show bigger price drops across the board.
 
Of the 22 metros where prices rose the most dramatically from 2002 to 2005, 17 of them slowed down in 2006. And that type of rapid slowdown can be just as strong a warning sign as a weak job market or a demographic shift.

Most are victims of their own success in recent years, forced into slow growth or even price declines as a way to shake out a market that's come a little too far, too fast.

Home prices in San Diego, the fastest decelerating market in 2006, are considered by mortgage insurer PMI Group as having better than a 60% chance of falling over the next two years. That's because the 18% appreciation the city averaged over the previous four years outpaced income growth, making homes unaffordable for too many people.

At some point, prices need to fall back to get the market back into balance, though a generally healthy local economy should help pad the fall and prevent any real sustained downturn.

"The faster the deceleration, the more likely a market will go negative, it shows the market is dropping fast," Harris says. Many upscale markets manage to avoid price declines for a while, he says, as homeowners reluctant to sell at a loss pull their properties off the market, hoping to ride out the storm.
 
"But that doesn't mean they won't give in," he says.

10 slowing markets

City	2002-2005 median price change	Q2 2005-Q2 2006 median price change	Difference
San Diego-Carlsbad-San Marcos, Calif.	18%	5.6%	-12.5%
Santa Barbara-Santa Maria, Calif.	18.9%	7.1%	-11.8%
Sacramento-Arden-Arcade, Calif.	17.6%	6.5%	-11.1%
Yuba City, Calif.	20.1%	10.1%	-10%
Barnstable, Mass.	14.4%	4.9%	-9.5%
Providence, R.I. - Fall River/New Bedford, Mass.	15.2%	6.1%	-9.1%
Reno-Sparks, Nev.	17.8%	8.8%	-9%
Carson City, Nev.	17.8%	8.9%	-8.9%
Boston-Quincy, Mass.	11.5%	2.9%	-8.6%
Sandusky, Ohio	4%	-4.2%	-8.2%

To see Forbes.com's slideshow of 10 slowing markets, click here.