The sales outlook looks brighter for the holiday season, the National Retail Federation said Tuesday.

The NRF, the world's largest retail trade organization, raised its growth forecast Tuesday for the Christmas season to 6 percent from its September forecast of 5 percent.

"When we had made the forecast, Katrina had just hit," said Rosalind Wells, economist for the Washington-based trade group. "Everything looked pretty gloomy." But she said since then, she has seen strong economic indicators.

Wells cited stronger-than-expected retail sales in October and falling gasoline prices as the catalysts for upgrading the holiday forecast.

"We have so much momentum going into the holiday season, so much more than we anticipated," she noted.

NRF's move marks the first time that the association has officially upgraded its forcast during the holiday season. Total retail sales for last year's November-December period rose 6.7 percent, compared to the previous year. The figure excludes sales at automotive dealers, gas stations and restaurants.

Meanwhile, Michael P. Niemira, chief economist at the International Council of Shopping Centers, noted that he is sticking with his growth forecast for a 3 percent to 3.5 percent rise in sales at stores open at least a year for the November-December period. Same-store sales are considered the best indicator of a retailer's health.