Vehicle-based temperature measurements around four operational data centers in metropolitan Phoenix found warmer air in residential areas downwind of the facilities. Traverses conducted from June 18 through October 25, 2025 measured maximum downwind warming of 2.2 °C and average downwind temperatures 0.7–0.9 °C above corresponding upwind areas. Thermal signatures were detected 100–500 m from facility perimeters. The sites included CyrusOne, Aligned, and Digital Realty facilities in Chandler and NTT PH1 in Mesa. At CyrusOne, a 169 MW colocation campus, average temperatures were 0.8 °C higher 500 m downwind on June 18 and 0.5 °C higher during a separate August traverse. Measurements at Aligned found 0.7 °C warming, Digital Realty recorded a 1.0 °C average difference and about 2 °C maximum difference, and NTT PH1 recorded a roughly 0.9 °C signal 300–500 m downwind. Air-cooled data centers convert nearly all IT electricity consumption into sensible heat. NTT PH1’s 36 MW IT load is estimated to draw about 47 MW total and reject heat comparable to roughly 40,000 households, while the 169 MW CyrusOne campus is comparable to more than 180,000 households. The researchers describe the observations as initial evidence from a limited sample and plan broader measurements and microscale modeling to assess mitigation options.