Insights · Spray conditions
Spray conditions by the hour: Delta T, wind and rain
AgronomyNote reads the forecast for where you are and marks every hour against the limits spray labels are written around. You see whether conditions are inside them now, and when the next window opens if they are not.
The limits each hour is read against
Each hour is optimal, marginal or outside, and the card names the quantity that decided it. A marginal hour is drawn as a lesser window, so the two are never mistaken for each other.
| Optimal | Marginal | Outside | |
|---|---|---|---|
| Delta T | 3 to 8 | 2 to 3, or 8 to 10 | Under 2, or over 10 |
| Wind | 3 to 15 km/h | 15 to 20 km/h | Under 3, or over 20 km/h |
| Gusts | — | 15 km/h or more, and over 33% above the steady wind | Never on their own |
| Rain | Under 0.5 mm in the hour | — | 0.5 mm or more in the hour |
Every number is a published one. The wind limits are the 3 to 20 km/h restraint written onto many labels. The Delta T bands sit inside the Bureau of Meteorology’s chart as GRDC reproduces it, which prefers 2 to 8 and calls under 2 unsuitable: there the air is near saturation, droplets stop evaporating and stay airborne, and that is also when inversions form.
What you see
The next three days hour by hour, and the rest of the week as a count of hours inside the limits, without times: a window named five days out would be a number to plan around that is going to move.
Each window says how long it runs and what is limiting it, such as wind 15 to 18 from 9am, with a note when rain follows it, a frost comes before it or the heat passes 30°.
Night hours are judged by the same numbers as day hours, and the card says when an hour is at night: surface inversions form on most nights in cropping country, and a forecast cannot see one.
What it will not tell you
- Which window is best, or when to go. Ranking windows is a recommendation by another name, and AgronomyNote knows nothing about the product, the nozzle, the neighbours or what you can see from the boom.
- Whether there is an inversion. That takes a check on site.
- Anything that overrides the label. The label always prevails.
Questions agronomists ask
Where does the spray conditions forecast come from?
From the Open-Meteo forecast for where you are (weather data by Open-Meteo.com, CC BY 4.0). AgronomyNote works out Delta T from its temperature and humidity for every hour, and reads wind, gusts and rain beside it.
Is the spray conditions card spray advice?
No. AgronomyNote reports which hours of the forecast sit inside published limits. It never says which window is best or that you should spray, and the product label always prevails.
How is Delta T worked out?
From the forecast temperature and relative humidity, with the same formula as the free Delta T calculator, so the two always agree.
Does it show spray conditions at night?
Yes. A night hour is judged by the same Delta T, wind and rain limits as a day hour, and marked as night, because a forecast cannot see the inversions that form on most nights.
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