I find George Kirby and lefty Matt Strahm to be two below-the-radar pitchers. Given the weather conditions, home plate umpire and these starters being underrated, I'm going Under. 

Kirby has the potential to be a star pitcher. He's backed by a Seattle bullpen that has the seventh-lowest ERA in the majors. 

Strahm has a 3.00 ERA and 27 strikeouts in 18 innings. The Mariners are batting only .206 against southpaw pitching. The Under has cashed the last six times the Mariners have gone against a lefty starter. 

Andy Fletcher is slated to be the home plate umpire. The Under is 36-15 (71 percent) the past three years when Fletcher has been behind the plate. 
This is a day getaway game. The weather isn't a plus for offense with the forecast being cloudy with temperatures only in the low 50's.