On most fair-weather days the surface wind is lightest around dawn and again in the evening, and strongest and gustiest in the afternoon, when the sun stirs faster air down from above. Summer adds thermals and afternoon showers; winter adds fronts, cold batteries and short days. In Altiwind, a flying window shows up as a run of green hours in the hourly timeline.
The daily wind cycle
The US National Weather Service describes a cycle driven by the sun:
- Morning: as the ground warms, bubbles of warm air rise and mix the lowest few thousand feet. The faster wind from higher up is brought down to the surface.
- Afternoon: the mixing peaks. Gusty surface winds usually start late in the morning, peak in the afternoon and die down by early evening.
- Evening and night: the ground cools, a stable layer forms near the surface and cuts it off from the air above. Surface winds drop and the gusts end.
- Predawn: low-level winds are at their most uniform.
There is a catch for drones. At night and around dawn, the calm layer can be shallow, and the NWS notes that the change to stronger wind above can happen over 100 ft (30 m) or less. That is right in the band where drones fly. Calm at the take-off spot does not mean calm at 120 m, so check the wind at altitude and not just the ground.
The cycle also gets overridden. A deep low-pressure system or a strong pressure gradient can keep it windy all day and all night.
Summer: thermals and afternoon storms
- Thermals. Strong sunshine heats the ground unevenly, and rising air makes the afternoon bumpy and gusty. If the air is moist enough, cumulus clouds form at the top of the mixed layer, a sign the air below is turbulent.
- Showers and thunderstorms. In the warm months, the NWS notes that thunderstorms are most common in the late afternoon and evening. Storms bring sudden strong gusts, heavy rain and lightning.
- Heat. Many DJI drones list 40 °C (104 °F) as their upper operating limit, and batteries and phones dislike direct sun.
- Long days. In London, daylight lasts about 16 h 38 min at the June solstice, so there is room to wait for the calm hours.
Summer windows tend to be early morning and the evening. Early morning often has the lightest wind and the best light for photos, with the caveat about wind aloft above.
Winter: fronts, fog, cold and short days
- Fronts. The Met Office explains that the jet stream is strengthened in winter, when the temperature contrast between the poles and the equator is greatest. A strong jet steers low-pressure systems and their fronts across the Atlantic towards the UK and western Europe. Windows often appear between systems, under a ridge of high pressure.
- Calm high pressure. Settled winter highs bring light winds but also fog and frost, especially after clear nights.
- Cold batteries. Below 5 °C Altiwind shows a battery warning. See flying drones in cold weather.
- Short days. In London, daylight lasts only about 7 h 50 min at the December solstice.
With weaker sunshine, the afternoon boost to surface wind is usually smaller in winter, and the passing weather systems matter more than the time of day. Midday often wins on warmth, light and cleared fog, as long as the wind allows.
Seasons at a glance
| Season | Often the best hours | Watch for |
|---|---|---|
| Summer | early morning, evening | thermals, afternoon showers and storms, heat |
| Winter | late morning to early afternoon, between fronts | fronts, fog, cold batteries, short daylight |
| Spring and autumn | either end of the day | quick changes, showers, morning fog in autumn |
These are tendencies, not rules. Your spot, the coast, hills and the day's weather pattern matter more.
Finding a window in the hourly timeline
- Pick your height. Choose 30, 60, 90 or 120 m. The window at 120 m can be shorter than at 30 m, especially at dawn and dusk.
- Scan for a run of green hours. Each hour is scored on sustained wind, estimated gusts, rain chance, temperature, visibility, Kp and daylight. The worst check decides the colour.
- Read the reason chips on amber hours. A cold-battery warning at 4 °C is a different decision from gusts at 95% of your drone's rating.
- Check daylight. Altiwind scores daytime as within your limits, civil twilight as marginal and night as outside your limits, using sun times computed on your device. For night flying, check your local rules. See twilight and night flying.
- Re-check before you leave. Forecasts update through the day, and the verified badge shows how the model has done against the nearest airport.
Altiwind shows today and the next 24 hours.
Sources
- NOAA/NWS, The Front, February 2014 ("Daily wind changes in the lower levels of the atmosphere")
- NOAA/NWS Spokane, Thunderstorms and severe weather spotting
- Met Office, What is the jet stream and how does it affect our weather?
- Met Office, Fog
- NOAA Global Monitoring Laboratory, Solar Calculator (day lengths)
FAQ
What time of day is least windy for flying a drone?
On fair-weather days, surface wind is usually lightest around dawn and in the evening, and gustiest in the afternoon. Check the wind at your flying height too, because it can stay strong above a calm surface.
Why is it calm on the ground but windy at 100 m in the morning?
Overnight cooling creates a stable layer near the ground that cuts it off from the faster air above. The change can happen within 30 m, so the drone can climb out of calm air into a much stronger wind.
Is winter or summer better for drone flying?
Each has its own windows. Summer gives long days and calm early mornings, but bumpy afternoons and storms. Winter gives calm high-pressure days between fronts, with cold batteries, fog and short daylight.
How far ahead can I plan a flying window?
Altiwind covers today and the next 24 hours, from regional models where they exist. Forecasts get less certain the further out you look, so re-check on the day.