40 km/h and 9°C: pricing the weather at Blackburn Rovers
The forecast at kick-off moves the expected goals in this match by about -12.4%. That is a real effect, it is small, and it is graded.
Why weather is worth less than people think
Every one of these effects is a few percent of a goal rate. Fitted on nine thousand matches with season dummies to absorb the fact that cold months are also different months, the temperature term is the only one that is comfortably distinguishable from nothing. A commentator's 'the conditions will suit them' is worth less than the difference between two mid-table defences.
What it does to the price
Applied to this fixture the adjusted rates are 1.30 and 1.17 against 1.30 and 1.17 unadjusted.
Weather from an hourly forecast at the ground's coordinates. Effects from a Poisson regression on 9,212 matches with season dummies; each is printed with its evidence grade on the Factor Lab.
Forecasts move, and a factor of a few percent is inside the model's own uncertainty band on most fixtures.