NEW YORK ( TheStreet) -- Home sales may be rising, but falling inventory poses challenges for buyers.

"We saw a drop in December inventory, the first decline in 16 months," Lawrence Yun, chief economist with the National Association of Realtors, said Friday in an interview with TheStreet. "Throughout 2014, we saw modest increases in inventory, but now we only have a 4.4-month of supply and that is beginning to re-accelerate prices."