Here is the latest forecast from the National Weather Service:
Today: A slight chance of showers before 11am, then a chance of showers and thunderstorms between 11am and 2pm, then showers likely and possibly a thunderstorm after 2pm. Mostly cloudy, with a high near 89. Southwest wind around 8 mph. Chance of precipitation is 70%. New rainfall amounts between a quarter and half of an inch possible.
Tonight: Showers and thunderstorms likely before 11pm, then a slight chance of showers between 11pm and 2am. Mostly cloudy, then gradually becoming mostly clear, with a low around 69. Northwest wind 5 to 7 mph. Chance of precipitation is 60%. New precipitation amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.
According to the Washington Post, MLB is working on a contingency plan to account for the rain:
“It would be dependent on a lot of factors — the forecast being the main one,” Pat Courtney, baseball’s chief communications officer, said Sunday. He said the league would be in close contact with both Fox Sports, its broadcast partner, and the MLB Players Association over any weather-related decisions.
The first priority would be to start on time Tuesday night, even if rain later in the evening forced a shortened game — as occurred in 1952 in Philadelphia. In 1961, the second of two All-Star Games held that summer ended in a 1-1 tie when the game was called for rain after the ninth inning. They remain the only rain-shortened All-Star Games.
Although MLB controls the decision whether and when to start the game Tuesday night, a move to Wednesday would require coordination with the players’ union, owing to the travel plans of the players. The season’s second half used to start on the Thursday after the All-Star Game but now begins on the Friday after the game.
If rain delays the start of Tuesday night’s game, every effort would still be made to get the game in, but there would be a point, probably sometime before 11 p.m., when the league would no longer want to start it. At that point, the focus could shift to Wednesday.