by Calculated Risk on 3/04/2013 09:53:00 AM

There has always been a clear seasonal pattern for house prices, but the seasonal differences have been more pronounced in recent years.

Even in normal times house prices tend to be stronger in the spring and early summer than in the fall and winter. Recently there has been 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 had a larger negative impact on prices in the fall and winter.

However, house prices - not seasonally adjusted (NSA) - have been pretty strong over the last few months - at the start of the normally weak months.

Click on graph for larger image.

This graph shows the month-to-month change in the CoreLogic and NSA Case-Shiller Composite 20 index since 2001 (both Case-Shiller and CoreLogic through December).   The seasonal pattern was smaller back in the early '00s, and increased since the bubble burst.

The CoreLogic index was positive in both the November and December reports (CoreLogic is a 3 month weighted average, with the most recent month weighted the most).

Case-Shiller NSA turned negative month-to-month in the October report (also a three month average, but not weighted), but was only slightly negative in November and turned positive in the December report.   This shows that the "off-season" for prices has been pretty strong this year.

The second graph shows the seasonal factors for the Case-Shiller composite 20 index. The factors started to change near the peak of the bubble, and really increased during the bust.

Note: I was one of several people to question this change in the seasonal factor - and this led to S&P Case-Shiller reporting the NSA numbers.

It appears the seasonal factor has stopped increasing, and I expect that over the next several years - as the percent of distressed sales decline - the seasonal factors will slowly move back towards the previous levels.