The HPI is a weighted, repeat-sales index, meaning that it measures averageprice changes in repeat sales or refinancings on the same properties. This
information is obtained by reviewing repeat mortgage transactions on single-family properties whose mortgages have been purchased or securitized by Fannie Mae or Freddie Mac since January 1975. The HPI is updated each quarter as additional mortgages are purchased or securitized by Fannie Mae and Freddie Mac. The new mortgage acquisitions are used to identify repeat transactions for the most recent quarter and for each quarter since the first quarter of 1975.
It should be made clear that these data are from house purchases using conventional, conforming loans up to the limit of $417,000 - so they do not capture the 'expensive' house market which is a bit more volatile.
This second picture are the same data but expressed as percentage change from the previous quarter.
It does appear that Bend and Medford are more dramatic than other Oregon cities both in the heating up and the cooling off.