Ref FAR 121.617

If your departure airport is below your landing minimums at that airport (not limited to Cat I, may use CAT II or Cat III minimums if aircraft and airport are both so equipped), you must file a takeoff alternate.

The takeoff alternate must be within 1 hour flight time for a two engine aircraft, or two hours for a three or more engine aircraft, with one engine inoperative.

The takeoff alternate must meet normal alternate weather minimums.

Note: Since alternate weather minimums are significantly higher than normal landing minimums, there very well could be closer airports with legal landing minimums that would not meet weather minimums for a takeoff alternate

Joe