In July 1999 the Mariners traded in the fully enclosed Kingdome for the never enclosed Safeco Field. Yes, the now T-Mobile Park does have a retractable roof, but unlike any other in MLB it serves as an umbrella for the field rather than a total enclosure. The roof’s main purpose is to prevent rain-outs and it only takes about 10 minutes to protect the playing surface from the showers that so frequently occur in Seattle. Although it’s sometimes used to keep the stadium warm on particularly cold nights, it’s left open even on the hottest days.
While the unique roof gets a lot of attention, it isn’t used very often as 85% of games are played with it left open. Perhaps the most defining feature of T-Mobile Park is the short distance that fly balls tend to carry. According to the Ballpark Pal distance model, balls hit more than 300 feet typically carry about 1.3% less than the MLB average, attributed partly to the sea-level altitude and below average temperatures in Seattle.
It seems the stadium architects anticipated relatively short carry distances as the field measures 5th smallest in MLB. It’s most comparable to
Great American Ball Park in Cincinnati as the dimensions around the perimeter are very similar. Like GABP, nearly every portion of the outfield fence is a bit closer than standard. Given the smaller dimensions, Ballpark Pal rates T-Mobile Park above average for home runs (7th) and particularly difficult for in-play hits as outfielders have much significantly less ground to cover. Overall, the venue is rated 26th for singles, 28th for doubles and triples, and 26th for total runs.
The wind blows from left-to-right 62% of the time at T-Mobile Park (vs just 16% in the other direction), but it only averages about 5 mph. Even when it's blowing hard it isn't that impactful as the venue is rated 22nd for wind receptiveness.
