The National Association of Home Builders’ Improving Markets Index grew to 99 metro areas in its February iteration, the most since the index was begun in September.

To arrive at an index number, the model measures how much above a bottom each areas is in housing permits, home prices and employment.

NAHB adds and removes metro areas every month as the numbers change. The organization offered a look at the 10 metro areas that have been in the index the longest. They are Bismarck, N.D.; Casper, Wyo.; Midland, Texas; Pittsburgh; Amarillo, Texas; Fayetteville, N.C.; McAllen and Odessa, Texas; Waterloo, Iowa; and Winston-Salem, N.C.