Precip chance: Chance of rain at game time
Temp (F): Temperature in degrees Fahrenheit
ADI: Air Density Index - formula combining altitude, air pressure, humidity & temperature
Wind: Wind speed and direction
WxRHB: How the weather impacts right-handed batters projections for this slate
WxLHB: How the weather impacts left-handed batters projections for this slate
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Why care about MLB DFS Weather?
In NBA and NHL DFS, we never have to worry about the weather (except for leaks in the roof, we’re not pointing fingers, New Orleans). In football, there are rare cases where heavy winds and precipitation can alter the outcome of a game. But for MLB DFS weather is an important part of your daily fantasy baseball strategy and research for every single slate.
Not only do we have to worry about rainouts -- in which games are postponed and you receive 0s in your lineup for any players from that game -- but other atmospheric conditions can have dramatic effects on fantasy scoring. Here are the factors you should be taking into account for your daily fantasy baseball strategy:
Temperature: Simply put, hotter temperatures = higher scoring for MLB teams and your fantasy teams. Research shows that there’s an average .037 ISO difference in 90-plus degree weather versus sub-40 degree weather. Below 60 degrees, teams averaged around 4.2 runs per game. When the temperature is 80-plus? That number jumps to more than 4.7 runs per game. This is especially important at the beginning and end of the season when there are massive weather differences between northern and southern ballparks. With all else equal, roster batters in warmer temps and pitchers in colder temps.
Air Density: Without getting too scientific, measuring the air density determines how “easy” it is for a ball to travel through the air. The thinner the atmosphere, the lower the air density, the farther balls will travel. We like to use the Neeley Scale discussed here. Coors Field is known for its high scoring games, mostly because of the low air density at a mile above sea level.
For MLB games, the Air Density Index from the link above will range between 40 and 70 usually, with a lower number being better for hitters. It can be tricky or tedious to find accurate air density data on a daily basis, but we conveniently incorporate it into our weather factor in the Occupy Model.
Wind Speed & Direction: Wind can suppress (or aid) fly balls in leaving the park depending on speed and direction. If wind is blowing in hard from left field, it will be much tougher for a right-handed power hitter to clear the fence. Kevin Roth of Rotogrinders does a great job of discussing wind effects for each slate -- he’s a near-must follow on Twitter.
Rain: In lower-risk contests, we should look to avoid games that have a high percentage of precipitation. This is obvious, as we want to avoid having 0s in our lineup if a game is postponed. But in higher-risk contests, it can be beneficial to roster hitters from rainy games for two reasons:
One, we’ll get lower ownership. DFSers will be scared of postponed possibilities, so we’ll get a break on ownership rates.
Two, hitters actually perform better in the rain. Jonathan Bales has research that shows teams score more runs and batters have a higher on-base percentage in games with precipitation.
If you do use players in games with rain, just be sure that the other three weather factors above are favorable.