The market for residential real estate last month mirrors the frustrating unpredictability of spring weather in the Puget Sound region. Data from the Northwest Multiple Listing Service for Western Washington shows that while listings for both single family homes and condos on Mercer Island were down a bit and the number of sales pending was flat, prices for the completed sales of single family homes rose more than 10 percent.

Meanwhile, the number of sales and prices lagged for Island condominiums.

The median closed sales price for Island single family homes that sold this past month was $878,000, up over 11 percent over a year ago. But the market for condos here remains slow. Last month there were just three completed condo sales, up one from a year ago. The median sale price for the three sold was $317,000. The median price for the two that sold in May 2009 was $430,000.

There was a total of 202 single family homes and condos listed for sale on the Island last month, down 10 percent from May 2009. In May 2010, 157 of the Island’s residential listings were single family homes, down from 190 a year ago. The number of sales pending for the month, for both homes and condos whose sales were in process but not completed, or closed, was 31, about the same as last May, when 33 units were in the process of selling. The 24 sales that were completed or closed last month were double the number a year ago, when just a dozen homes and condos sold.

At present there are 67 single family homes offered for sale on Mercer Island, priced at less than $1 million. Forty-six are priced between $1 million and $2 million, and 35 homes are priced between $2 million and $5 million.

There are six single family properties listed for sale above $5 million. One is a $32 million waterfront mansion off Boulevard Place. Another mega-home with waterfront and moorage along S.E. 22nd Street at the northwest corner of the Island is priced at $23.8 million, its price reduced from $28 million. Both are on lots of over one acre and have more than 13,000 square feet of living space. The Lytle house on Roanoke Way, previously listed for $40 million, is at auction with a $12 minimum bid required. An auction conducted earlier this spring, with the minimum bid set at $15 million did not yield a qualified buyer according to media reports.

As of June 7, there were 50 condominiums offered for sale on the Island. The most inexpensive is a 715-square-foot, one-bedroom condominium listed for $143,000.

At the other end of the pricing scale is a 3,400-square-foot, three-bedroom, three and one-half bath condo with a view, priced at $1.19 million.