The series comes from the 'Current Population Survey (Household Survey)'
The source code is: LNS13008397
Source: US. Bureau of Labor Statistics
Release: Employment Situation
US. Bureau of Labor Statistics, Of Total Unemployed, Percent Unemployed Less than 5 Weeks [LNS13008397], retrieved from FRED, Federal Reserve Bank of St. Louis https://research.stlouisfed.org/fred2/series/LNS13008397/, July 30, 2015.
FRED BlogTracking the duration of unemployment