Does Rain Affect NFL Over/Unders?
Rain moves NFL totals more than wind does, and the market under-prices it. Since 2015, outdoor games with rain or snow at kickoff landed 3.4 points under the closing total on average, and the under hit 64% of the time (152 games).
The numbers
| Conditions | Games | Vs closing total | Under hit |
|---|---|---|---|
| Dry | 2959 | +0.5 | 50% |
| Rain or snow | 152 | -3.4 | 64% |
| Rain or snow + wind 10+ mph | 64 | -5.3 | 75% |
How Gridline uses it
Adding a rain-or-snow flag to Gridline's totals model (Vegas total plus adjustments) raised its 2+ point leans from 56.5% to 58.5% in walk-forward testing on 2018 to 2025, and its 1.5+ point leans from 54.4% to 55.1%. Rain is worth about 2.8 points off the total in that model, more with wind.
Caveats: history uses the weather actually reported at kickoff, while bets are placed on forecasts, so real results will be weaker; and about 150 rain games is a small sample. Snow alone has barely moved totals (25 games).
More research
Projections are research, not betting advice. Sports betting is not legal in every state. If gambling stops being fun, call or text 1-800-GAMBLER.