by Calculated Risk on 8/24/2010 11:30:00 AM

Earlier the NAR released the existing home sales data for July; here are a couple more graphs ...

The first graph shows the year-over-year (YoY) change in reported existing home inventory and months-of-supply. Inventory is not seasonally adjusted, so it really helps to look at the YoY change.

Click on graph for larger image in new window.

Although inventory increased from June 2010 to July 2010, inventory decreased 1.9% YoY in July. The slight year-over-year decline is probably because some sellers put their homes on the market in the Spring hoping to take advantage of the home buyer tax credit.

Note: Usually July is the peak month for inventory.

This level of inventory is especially bad news because the reported inventory is already historically very high, and the 12.5 months of supply in July is far above normal.

The months-of-supply will probably decline in August as sales rebound slightly and some sellers take their homes off the market, but I expect double digit months-of-supply for some time - and that will be a really bad sign for house prices ...

A normal housing market usually has under 6 months of supply. The following graph shows the relationship between supply and house prices (using Case-Shiller).

This graph show months of supply (through July 2010) and the annualized change in the Case-Shiller Composite 20 house price index (through May 2010).

Below 6 months of supply (blue line) house prices are typically rising (black line).

Above 6 or 7 months of supply, house prices are usually falling. This isn't perfect - it is just a guideline. Over the last year, there have been many programs aimed at supporting house prices, and house prices increased slightly even with higher than normal supply. However those programs have mostly ended.

This is a key reason why I expect house prices to fall further later this year as measured by the Case-Shiller and CoreLogic repeat sales house price indexes, although I don't expect huge declines like in 2008. My expectation is further price declines of 5% to 10% on the repeat sales indexes.

Notes: The Case-Shiller house price index for June will be reported next week (really a 3 month average of April, May and June). We really want to see prices for July - and those will not be reported until the end of September. And once again the July numbers will be a 3 month average. So it might take until the end of October to see the price declines that are already happening in the housing market.