I don’t understand the iphone weather forecast icon. What does the horizontal weather icon on Thursday that looks like air currents mean?

Breeze, level 3 wind.

It belongs to the fourth wind level in the Beaufort wind scale, with wind speeds of 3.4~5.4m/s and 12~19km/h. . The wind power level is determined based on the wind speed value 10 meters above the ground on flat ground. Under normal circumstances, it is expressed as 0 to 12 to 13 levels, but under special circumstances, there are wind power levels above level 13. Level 3 winds are called breezes and are characterized by swaying leaves and twigs, unfurling flags, and swaying tall grass.

Extended information:

Special symbols representing various weather phenomena, cloud shapes, sky conditions, etc. Includes weather phenomenon symbols for observation records and weather graphic symbols for media dissemination.

When a meteorological observer observes a certain weather phenomenon, the corresponding symbol should be recorded in the "Weather Phenomenon" column of the observation book on that day, except for a few phenomena, and its start and end times should also be recorded. Based on these symbols, combined with the intensity, coexistence and certain characteristics of weather phenomena, a set of symbols that can be filled in on weather maps is called map-filling symbols.

Reference: Weather symbols? Baidu Encyclopedia