Within the surface boundary layer, the part of the atmosphere closest to the ground, wind speeds typically increase linearly with the natural log of the height above the canopy. When 25 km/h wind speeds are reported, they are at 10 m, not the 1 m height where the boom is located. The international standard for wind speed measurement is 10 m above ground level. This is because even low-drift spray contain enough fine droplets to cause damage if they linger.

In comparison, nothing (except not spraying) can be done to reduce risk during inversion conditions. All these practices reduce drift when it’s windy. We can mix the next tank in higher water volume, forcing either a larger nozzle (larger flow rates of the same model nozzle usually produce coarser sprays) or slower travel speeds.

We can lower the boom or lower the spray pressure. If it’s windy, we have options to respond. In a calm environment, such turbulent eddies don’t exist. Wind creates mechanical turbulence which helps sprays deposit and disperse. This is not possible with calm conditions because inversion air flow may follow terrain, and as inversions dissipate, the first daily winds can be changeable and unpredictable in direction. We can assess the risk to downwind sensitive areas. In fact, wind provides several advantages over calm conditions: But the “negative-only” perspective is being re-evaluated in light of dangers associated with wind-free conditions that often occur during temperature inversions (see “Temperature”, below). Yes, droplet displacement increases with wind speed. We’re conditioned to think of wind as having a negative effect on spray drift. While they aren’t forecasts per se, visualizing wind patterns over a larger region allows a better understanding of what’s coming your way.įigure 1: Sites such as offer powerful visualizations of current and future wind conditions. These services show trends over time in a great visual interface, allowing users to anticipate changes in wind speed and direction for better planning.

Consider wind speed sites such as Windfinder, Ventusky, or Windy for added insight. At any instant, the wind speed and direction may be acceptable for our planned spray job, but we know that it will change. It’s standard practice to look a day or two ahead for wind forecasts. Here’s how can we improve our understanding of wind and its impact. Let’s have a closer look at what each weather component contributes to the decision.Įveryone knows that small droplets can drift if it’s windy, and the windier, the worse it is. More often than not, the suitability of the weather is the main factor in the decision to spray. It’s time to spray and what’s the first thing you do? Check the weather forecast, of course.

Sc dew 101