The Weather Project · Delta-T & application planning
Spray weather and Delta-T forecasts
Identify periods worth checking for spray operations. View evaporative conditions alongside model wind, then confirm the actual conditions and product-label requirements at the site.
Understand the product
What is Delta-T?
Delta-T is air temperature minus wet-bulb temperature, expressed in degrees Celsius. It describes evaporative conditions: larger differences indicate greater evaporative demand. It is one part of spray planning alongside wind, humidity, droplet choice and the chemical label.
What do the spray categories mean?
The example screening configuration uses outer wind limits of 3–20 km/h and Delta-T limits of 2–10°C. Within those limits, caution begins at wind of 15 km/h or Delta-T of 8°C. The map labels preferred, caution and do not spray refer to those configured weather checks; they are not universal chemical-label limits. Read the legend on the current map.
How to use the viewer
Open the Agricultural Weather Explorer, choose your region and select Delta-T or Spray-condition guidance. Step through the valid times to identify a potential window. Check nearby wind-gust forecasts as well as mean wind, then measure conditions at the application site.
What the map cannot establish
The wind input is modelled at 10 m and can differ from conditions at boom height. This screening map does not detect temperature inversions or assess mandatory buffers, sensitive downwind areas, equipment settings or all label restrictions. A preferred category does not establish that an application is suitable.
See what the maps look like
Examples illustrate the format and legend. They are not a live forecast briefing; use the forecast viewer for the latest available run and valid time. Select an image to open it at full size.
From the map to your site
Open the forecast viewer, choose your region and product, then read the model run and local valid date. Compare related maps over matching periods and check local observations before making a time-sensitive decision. Longer-range forecasts are best used for planning and reassessed as the date approaches.
Common questions
Can I plan a spray window from Delta-T alone?
No. Use it alongside wind direction and speed, gusts, local inversion checks, the chemical label and on-site observations.
Where are the two products?
In the agricultural viewer, select Delta-T for the continuous temperature-difference map or Spray-condition guidance for the combined screening categories.
Independent model guidance from The Weather Project. Check the map’s method, coverage and valid period. Regional guidance complements local measurements and crop-specific advice.