What It Tells You
The spray window is the run of forecast hours in which a spray will land and stay where it is put. Delta-T is the gap between air temperature and wet-bulb temperature. Too low and droplets persist and drift in still air. Too high and they evaporate in flight. An hour is suitable when delta-T is between 2 and 8, the wind is between 3 and 19 km/h and less than 1 mm of rain is close. The card shows up to five windows over the next 48 hours. The windows are computed by the Spray Window model. The same model gives the frost risk for the next three nights.How It Works
Every three hours the model reads the field’s cached hourly forecast. It evaluates each of the next 48 hours against the delta-T, wind and rain bands and joins contiguous suitable hours into windows. A suitable current hour with a window ahead raises an advisory once in 24 hours.
Green bands mark the suitable hours over the next 48, the frost cuts one short, and the sprayer waits.