It will truly be a miracle if we can get through Wednesday without at least one MLB game being called off due to weather.  There are a few that could be impacted.  It is important to understand a sportsbook's rules pertaining to suspended and postponed games, some of which differ across the board.

Remember that forecasts are subject to change. 

General Rules Pertaining to Types of Bets

If the game is postponed before it begins and is not played within 48 hours of the original start time, all bets are voided, and your stake is refunded at most online sportsbooks.

If the game starts but is suspended and not completed within 48 hours, bets are voided unless the outcome of a specific market has already been determined at most online sportsbooks.

Impacts on Types of Bets

• Single Bets: These are voided if the game isn't completed within the 48-hour window, and your stake is returned.​
• Parlay Bets: If one leg of your parlay is voided due to a postponed game, that leg is removed, and the parlay continues with the remaining selections. The odds and potential payout are adjusted accordingly.
• Player Props: These require all listed players to be active. If a player doesn't participate, the bet is voided.

Totals

If the game goes at least 9 innings (or 8.5 if the home team is winning), the total bet is counted and will be graded accordingly based on the score at the time of suspension.

Should the game be called off prior to 8.5 innings (or 9 full innings if the visiting team is ahead), the total bet is voided at most books. It will therefore be marked as "no action" and refunded in most cases.

In the event of a game suspension that resumes the next day (or within 24 hours), the game is deemed as "unofficial" as it applies to totals bets.  Therefore, they are voided.  However, some books do treat suspensions when resumed the next day differently in regard to totals so it is important to check individual sportsbook rules.

Which Games Could Be Impacted Wednesday

From RotoGrinders:

Indians vs. Twins Game 1: Off and on rain all day again in MIN. The rain is light, and they need to play, so I think they are just going to play in the rain... but it's fairly miserable with temps in the 40s, so they may decide it's not doable. Will need to tarp-watch pregame on this one to see what they decide.

Game 2: Again, it's off and on rain all day in MIN with cold temps. This is less about weather and more about whether or not they want to subject fans and players to misery, will need to see how Game 1 goes, that should be fairly telling for Game 2.

Braves vs. Nationals: Looks like it rains most of the game, light at first, but eventually too heavy to play through. I don't know what the plan here is, but there's not really a good one that I can see (maybe try to play on time, eat a very lengthy delay, then finish late night?). Certainly some PPD risk here, especially if they announce a late start.

Rangers vs. Yankees - This game is in-between WASH and BOS, both in forecast and geographically speaking. The rain isn't as light as Boston where I'm certain they will play through... nor is it as heavy as WASH where they can't play in the rain, it's somewhere in the middle. My best guess this far out is that they play on time in some light rain, then battle through gradually increasing rain to get as much (possibly all) of the game in before it just gets too soaked. Temp in the 50s, winds in at 10mph, just gross weather for baseball all around. Oh and if they Late Start this game it's over, that's nearly a surefire "PPD incoming" sign.