After an hour delay to the start of last night's game, and a forecast that saw more storms move in later in the evening, last night's Sporting KC game against the Colorado Rapids was postponed to a later date.
MLS rules on game postponements state that games that are delayed have to be restarted before 12am local time and must finish before 1am. With the fact that the game hadn't started and more storms moving into the area, there was no way the team would have been able to kick off before 11:15pm or so to get the full game plus stoppage time in before the 1am deadline.
League rules also state that the game should be replayed today, 5/17. That though was ruled out as an option last night because of Sporting KC's upcoming schedule. The team already has a league game scheduled for Wednesday at home against New England and a game next Saturday scheduled against Seattle so Peter Vermes was probably very adamant about not playing the game today.
The game is actually the third postponement due to weather in KC's history, the second at home. Back in 1998 a game between the Wizards and DC United at Arrowhead on June 20th was canceled in the 53rd minute and was made up in full over two months later on August 26th. KC also had a game against the Chicago Fire in the US Open Cup on August 2nd of 2006 delayed for two weeks until the 14th after thunderstorms postponed the game.
As for the potential make up game, KC and Colorado have two weekends where both teams are off, June 13-14 and September 5-6. If the two teams can't agree to play on either of those dates, the likely date will be some time in the middle of the week.