Metro Phoenix sees first 100-degree day of year Sunday marked the Valleyâ€™s first 100-degree day of the year and the century mark is likely to be reached again today, the National Weather Service says. :heat: The highs through the rest of the week are expected to be in the 90s. Sundayâ€™s official high at Sky Harbor Airport was 100. On average, the first 100-degree day strikes May 2. Last year, it arrived April 21. This weekâ€™s high temperatures are expected to be mitigated by a low-pressure system that will brush Arizona by Tuesday. That should bring in a breeze Wednesday through Friday, according to Valerie Meyers, a meteorologist with the Weather Service.