April not only brings April Showers, but also May Sweeps which start on Thursday.
This year, the month long period will run from Thursday, April 23rd, through Wednesday, May 20th, thanks in part to an early Memorial Day holiday on Monday, May 25th.
Nielsen likes to wrap up the survey period prior to the holiday since viewing generally decreases over the long weekend with people doing other activities and watching less television - in theory and a normal economy. In fact, May 21st through May 27th is a "non reported" week by Nielsen terminology.
May sweeps will be the last analog book for the remaining stations who will finally convert to all digital on June 12th, including all those in the Cleveland market.