Home prices in 20 U.S. cities surged in December, with low mortgage rates fueling the housing market.

The S&P CoreLogic Case-Shiller index of property values climbed 10.1% from a year earlier, beating the median estimate of 9.9% in a Bloomberg survey of economists. It followed a 9.2% gain in November and was the biggest jump since 2014.

Phoenix, San Diego and Seattle posted the biggest gains in prices, according to a press release on Tuesday. Nationally, the Case-Shiller index jumped 10.4% in December, also the biggest surge since 2014.

Historically low mortgage rates have fueled a pandemic housing rally, with a scant inventory of homes to buy helping to boost prices.

The Space Needle stands past a “For Sale” sign displayed in front of a house in Seattle, Washington.

Mike Kane/Photographer: Mike Kane/Bloomber

December was the fourth straight month that prices gained the most since 2014. The rally started in July and picked up steam in the final months of 2020, with Americans looking to take advantage of low borrowing costs to buy suburban homes.

“These data are consistent with the view that Covid has encouraged potential buyers to move from urban apartments to suburban homes,” said Craig Lazzara, global head of index investment strategy at S&P Dow Jones Indices.

Prices gained 14.4% in Phoenix, leading all cities for the 19th straight. In the West, the overall gain was 10.8%.

But the price growth is likely to slow this year, according to CoreLogic Deputy Chief Economist Selma Hepp.

“Acceleration in price growth is largely driven by record-low mortgage rates and the severe undersupply of for-sale home — two factors that may take a turn this year and relieve some of the price pressure,” she said. “But, demand from millennials and existing owners, who may have been on the sidelines throughout the pandemic, is likely to persist.”