by Calculated Risk on 11/25/2012 10:32:00 AM

This is just a reminder: The Not Seasonally Adjusted (NSA) monthly Case-Shiller house price indexes will show month-to-month declines soon, probably starting with the October report to be released in late December. The CoreLogic index has already started to decline on a month-to-month basis. This is not a sign of impending doom - or another collapse in house prices - it is just the normal seasonal pattern.

Even in normal times house prices tend to be stronger in the spring and early summer, than in the fall and winter. Currently there is a stronger than normal seasonal pattern because conventional sales are following the normal pattern (more sales in the spring and summer), but distressed sales (foreclosures and short sales) happen all year. So distressed sales have a larger negative impact on prices in the fall and winter.

In the coming months, the key will be to watch the year-over-year change in house prices and to compare to the NSA lows in early 2012. As an example, the September CoreLogic report showed a 0.3% month-to-month decline in September from August, but prices were up 5.0% year-over-year. That was the largest year-over-year increase since 2006.

I think house prices have already bottomed, and that prices will be up close to 5% year-over-year when prices reach the usual seasonal bottom in early 2013.

Click on graph for larger image.

Note: The Case-Shiller September report will be released this coming Tuesday. For this graph, I used Zillow's forecast for September.

This graph shows the month-to-month change in the CoreLogic and NSA Case-Shiller Composite 20 index over the last several years. The CoreLogic index turned negative in the September report (CoreLogic is 3 month weighted average, with the most recent month weighted the most). Case-Shiller NSA will probably turn negative month-to-month in the October report (also a three month average, but not weighted).