How Weather Actually Impacts NFL Betting

Isolating what the forecast has in store for NFL games can help you make smarter football bets.

Of the four major American sports, the NFL has always been unique in its lone willingness to brave the weather for its games.

The NBA and NHL exclusively play indoors, and MLB will call games or use retractable roofs when the conditions become too harsh. Sure, football has its fair share of domes, but the large majority of NFL venues are entirely open to the will of Mother Nature.

That's not to knock games played in domes. Having perfectly controlled conditions to play in lends its hands to more high-scoring affairs: games in domes average almost four more points than games played outdoors. And although we know scoring has been outpacing Vegas totals for some time now, the effect is even more observable in domes. Games in domes outpace overs by more than twice as much (1.6 points on average) as outdoor games do (0.7 points).

With that in mind, it's essential to know what to look for when handicapping the outdoor elements. Missing even one key weather factor can tip a game in or out of betting consideration and lead to unrealized profits or misled losses. Whether it's wind, precipitation, or temperature, it's crucial to account for everything.

Wind

The wind is the most reliable and predictive of the weather factors as the largest sample size. The average wind speed for an NFL game is around seven miles per hour, so use that as your baseline when looking at a slate’s weather conditions.

From there, every passing metric decreases as wind speed increases, whether it’s raw production (passing yards, passing touchdowns, etc.) or efficiency (completion percentage, yards per attempt, QB rating, adjusted net yards per attempt, etc.).

The wind hits passing production more significantly than passing efficiency, but overall we should expect scoring as a whole to decrease as wind speeds increase.

One caveat is that the wind's effect on passing is much more drastic once it hits 20+ mph. The decrease going from 0-10 mph to 10-15 mph is about the same as going from 10-15 mph to 15-20 mph, but the decrease is about 1.5-2.0x as large when going from 15-20 mph to 20+ mph. That’s not to undermine wind speeds from 10-20 mph but to emphasize the importance of a game hitting 20+ mph.

Another thing to consider with wind is kicking field goals. Bettors make common mistakes when analyzing kicking data in windy conditions, and the most significant error is when looking at “mild” wind (10-15 mph).

The difference is almost negligible when looking at field goal percentage in 0-15 mph winds (~83%) vs. 15-20 mph (~80%). As a result, the common conclusion is that wind doesn’t affect field-goal kicking up to 20 mph, but that is a bit misleading.

The first thing to establish is obvious: field goal percentage is a product of field goal distance (the shorter the field goal distance, the more likely it will convert).

So the thing to note is that the average distance of field goals attempted in windier conditions (15-20 mph wind) is shorter than in favorable conditions (0-15 mph). This makes sense: a coach is much less likely to try a long field goal the windier it is.

So if field goals are made at similar rates in more windy conditions than in favorable conditions despite the field goals being of shorter distance, then the wind is a factor.

This effect, much like passing, is much worse when we reach 20+ mph winds. At 20+ mph winds, the average field goal distance drops around seven yards from the average, and the conversion rate drops around 6%. But again, we have to consider the expected rate given the lower field goal distance.

In 20+ mph winds, the much shorter average field goal distance should yield an expected make rate of nearly 89%, yet only 77% of kicks are made. To put it quite simply, that is a massive discrepancy.

Precipitation

Precipitation is a trickier weather condition to handicap. The sample sizes for precipitation are a bit hard to work with reliably because it can be challenging to isolate precipitation’s actual effect on play versus the compounding product coming from other weather effects commonly present during rain (wind) and snow (wind and temperature). 

Generally speaking, there is no difference between light rain, moderate rain, or heavy rain. 

This probably seems wrong intuitively, as it is easy to imagine players slipping around everywhere in a torrential downpour. However, it is important again to remember that we are trying to isolate precipitation from other conditions. 

Nevertheless, the presence of rain decreases passing production by around 12%.

There is, however, a difference between light snow and heavier snow. Despite what you might think, light snow alone has a very negligible effect on passing production. Compared to games played in ideal conditions, passing production only decreases by 2% in light snow.

This is a massive contrast to heavier forms of snow, in which passing production drops by 25% on average.

When it comes to field goals, both rain and snow certainly have an effect. In the presence of no precipitation, the field goal percentage is about equal with the expectation to distance (~83%). With rain, field goal percentage jumps to around 85%, but this is because (like with wind) the average distance is noticeably lower.

Despite the shorter attempts in the rain, the field goal percentage is around 2% lower than expected.

Snow, on the other hand, has a much more significant effect on field goal kicking. Field goals in snowy conditions convert at just a 76% rate, a 7% drop from the norm.

When adding the context of the much shorter attempts in snow, the 76% make rate is nearly 12% lower than the expectation of those shorter field goal attempts (88%).

Temperature

Temperature is relatively straightforward. There are typically no significant deviations in performance when looking at the temperature range of 55-85 degrees, which is generally considered "ideal" for this weather condition. Passing production dips 5% when going below the 25-55 degree range.

There is about an 8% decrease when looking at the extremes (<25 degrees or >85 degrees). 

And yes, that's it — pretty straightforward. 

Takeaways 

So here is what we should be looking for when looking at weather conditions:

It is crucial to keep in mind that although we spent this exercise isolating weather effects, you should be mindful of compounding effects (for example, rain with gusts) when looking at a slate's weather. All in all, this comprehensive look at weather's impact on NFL games should be a great tool in your arsenal moving forward.

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