Get ready, Las Vegas. The year’s first 100-degree heat wave is fast approaching, just in time for Mother’s Day weekend. Expect highs in the upper 90s for Friday and Saturday but there’s a 50 percent chance the valley will reach the century mark on Sunday, which is Mother’s Day, said Sam Meltzer of the National Weather Service. If the valley fails to hit 100 that day, it most certainly will reach that number Monday and Tuesday, with forecast highs of 104 and 103, which may break daily heat records, Meltzer said. How hot it gets this weekend depends on “the position of the high pressure system” over the Southwest, he explained. There’s a possibility that a heat advisory/warning could be issued, he said. On Thursday, Harry Reid International Airport hit 92 degrees at 3:59 p.m., about 10 degrees short of the daily record. It was the second time Reid has reached 90 this month (it saw 91 on May 3). The average early May temperature is 85 degrees. The last time Reid recorded a 100-degree temperature was Sept. 7.…