Unemployment rose in nearly all large U.S. cities in January compared to the previous month, mostly because of seasonal changes such as the layoff of temporary retail employees hired for the holidays.

The Labor Department says the unemployment rate rose in 351 metro areas, fell in only 16, and was unchanged in 5. That's worse than December, when the rate fell in 207 areas and increased in 122.

Other seasonal trends, such as the layoff of construction workers due to winter weather, also contributed to the widespread increase.

Nationwide, the unemployment rate dropped to 9 percent in January from 9.4 percent the previous month. It ticked down to 8.9 percent in February.

But the national data is seasonally adjusted, while the metro data isn't, which makes it more volatile.