# Spraying weather guides

> Practical guides to spray weather: Delta T, wind speed, spray drift, thermal inversion, humidity, rain, droplet size and drone spraying conditions.

- Canonical URL: https://pulvecast.com/guides
- Language: en
- Last updated: 2026-09-19
- Path: Home › Spraying weather guides
- Site guide for agents: https://pulvecast.com/llms.txt

Short, practical guides to the weather decisions behind every application — for boom sprayers, self-propelled sprayers and spray drones. The product label and your local regulations always come first; these guides explain the weather side of the decision.

## [Delta T for spraying: what it is and why 2 to 8 °C](https://pulvecast.com/guides/delta-t)

What Delta T is, how it is calculated from dry-bulb and wet-bulb temperature, why 2–8 °C is the spraying window and what happens below 2 and above 8.

## [Delta T chart: how to read it](https://pulvecast.com/guides/delta-t-chart)

A Delta T chart by air temperature (5–45 °C) and relative humidity (20–90 %), with the colour bands used for spraying and how to read it in the field.

## [Thermal inversion and spraying](https://pulvecast.com/guides/thermal-inversion)

What a thermal inversion is, when it forms, the signs to look for in the field, why spraying under one moves product off target and how to detect it.

## [Spray drift: causes and how to reduce it](https://pulvecast.com/guides/spray-drift)

What spray drift is, the difference between particle and vapour drift, the main causes — droplet size, wind, height, inversion — and practical ways to cut it.

## [Wind speed for spraying](https://pulvecast.com/guides/wind-speed-for-spraying)

The wind speed range commonly recommended for spraying, why dead calm is also a problem, gusts and wind direction, and how wind changes with height for drones.

## [The best time of day to spray](https://pulvecast.com/guides/best-time-to-spray)

When is the best time of day to spray? Trade-offs between early morning, midday, evening and night: dew, inversion, Delta T, heat, wind and pollinators.

## [Humidity and dew point for spraying](https://pulvecast.com/guides/humidity-and-dew-point)

How relative humidity and dew point affect spraying: evaporation when the air is dry, dilution and runoff when leaves are wet, and the humidity band to aim for.

## [Rain and spraying: rainfast periods and forecasts](https://pulvecast.com/guides/rain-and-spraying)

How rain affects spraying: rainfast periods on the label, reading precipitation probability, heavy dew, and the runoff risk to streams, ponds and water bodies.

## [Temperature and spraying](https://pulvecast.com/guides/temperature-and-spraying)

How air temperature affects spraying: evaporation, herbicide volatility and crop stress when hot; slow uptake and frost when cold; and the link with Delta T.

## [Droplet size and nozzle selection](https://pulvecast.com/guides/droplet-size-and-nozzles)

ASABE S572 droplet size classes from Very Fine to Ultra Coarse, the coverage vs drift trade-off, and how to match droplet class to wind and Delta T.

## [Weather for drone spraying](https://pulvecast.com/guides/drone-spraying-weather)

Weather for spray drones: rotor downwash, flight height and speed, wind limits vs spraying wind, wind at altitude, battery temperature, GNSS/RTK, Kp and rain.

## [Kp index, RTK and GNSS for spray drone operators](https://pulvecast.com/guides/kp-index-rtk-gnss)

What the Kp index means for spray drone pilots, how geomagnetic storms affect GNSS and RTK accuracy, which Kp values to watch and why visible satellites matter.

## [Pre-spray checklist](https://pulvecast.com/guides/pre-spray-checklist)

A practical checklist before any pesticide application: label, PPE, calibration, weather window, buffer zones, neighbours and beekeepers, equipment and records.

## Check the spray window before you go to the field

PulveCast gives a green, yellow or red verdict for every hour from Delta T, humidity, wind, gusts, drift risk and thermal inversion. Free on Android and iOS, no account needed.

- Google Play: https://play.google.com/store/apps/details?id=com.pulvecast.app
- App Store: https://apps.apple.com/app/pulvecast/id6779816829