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Abstract. Facility design on mechanically ventilated barns for dairy cattle continues to evolve as facility size increases to house more and larger groups of dairy cows. While there are many evaluations of the physio-environmental interactions of cows during the summer, there has been little discussion on the winter conditions for adult dairy cows in larger facilities. Meanwhile, winter ventilation recommendations have not changed in the last 25 years and continue to use volume-based recommendations (four air changes per hour). To elucidate temperature and humidity variations in a larger facility, this study aims to catalog the temperature and humidity distribution in a mechanically ventilated wide-tunnel barn during the winter months. A tunnel ventilated, located in South Dakota, was selected for this study. The barn is 144 m wide and 249.3 m long with 5.18 m sidewalls and an 8.1 m ridge. The study barn consists of a 22 stall rows organized into five sections of which four have two head-to-head pens and the last section (west side) has two three-row pens. The barn is a negative pressure mechanically ventilated tunnel barn equipped with chimneys at the ridge every 4.42 m and sidewall exhaust fans. Twenty-seven sensors were distributed lengthwise and widthwise of the barn and installed roughly 2.4 m. above the stall floor. Sensors, sampling every 10 minutes from January 13th to March 28th, were distributed across the barn to evaluate length and widthwise temperature and humidity gradients. Results show that the wide-tunnel barn design adequately shifted the temperature gradient from end to end of the barn into a flow from the ridge to the sidewalls. While the assumption of homogeneous temperature and humidity within the barn may hold in higher temperatures, it is not an accurate assumption for winter ventilation where differences of up to 17°C exist within the barn.