Most cancelled drone flights are not cancelled by a rule. They are cancelled by weather — or they should have been. A small multirotor lives entirely inside the lowest hundred metres of the atmosphere, which is exactly where wind gusts, turbulence, fog, and icing do their work, and a pilot who can read a weather briefing makes the go/no-go call before leaving the house instead of discovering it mid-flight. It is also the part of drone theory the A2 exam leans on hardest: meteorology is the first of its three themes.
The good news is that a useful drone weather briefing takes about five minutes and rests on a handful of readable facts. Here is what actually matters.
Gusts decide, not the average wind
Every consumer drone has a rated wind resistance — for small multirotors typically somewhere around 10–12 m/s, and the exact figure is in the manufacturer's specification, not in folklore. The mistake is to compare that figure against the average wind in the forecast. The number that loads the airframe is the gust: a short burst of stronger wind that arrives faster than the flight controller would like, exactly when you are close to an obstacle or holding position for a shot.
Aviation weather reports make the distinction explicit. A wind entry of 27012G22KT reads: wind from 270° (west), mean speed 12 knots, gusting to 22 knots. Aviation wind comes in knots, and the conversion is worth memorising: 1 knot ≈ 0.514 m/s. So 22 knots of gust is about 11.3 m/s — already at the ceiling of a typical small drone's rating, even though the 12-knot average (6.2 m/s) looks harmless. A 25-knot gust is about 12.9 m/s, past the limit of a drone rated at 12. The planning rule is simple: compare the gust figure against the rated limit, and keep a margin. Flying in gusty air near the rated ceiling risks control problems and, at worst, losing the aircraft downwind.
The wind you cannot see from the ground
A surface observation describes the wind at roughly head height at an aerodrome. Your drone does not fly there. At 80–120 m above ground the wind is usually stronger than at the surface — often noticeably so over open terrain and near the coast — because surface friction slows the lowest layer of air. The safe planning assumption is that the wind at operating height exceeds the reported surface wind, and that calm at the launch point proves nothing about conditions at 100 m.
Terrain adds its own hazards. Buildings, tree lines, and hills produce mechanical turbulence — rotors and eddies on their downwind side. Streets between tall buildings funnel and accelerate wind (the urban canyon effect), and rooftops shed vortices exactly where an inspection flight wants to hover. Separately, a drone that suddenly gains or loses speed and altitude with no control input has usually crossed a wind shear layer — a rapid change of wind speed or direction over a short distance, which in strong cases can destabilise a small UAS entirely. If the aircraft starts flying like that, the correct response is not to fight it for the shot; it is to bring the aircraft back.
METAR and TAF: five minutes of aviation-grade weather
The tools pilots of crewed aircraft use are free, public, and short enough to read while your batteries warm up.
A METAR is a routine aerodrome observation, issued typically every 30 or 60 minutes. It is a snapshot of what the weather is: wind with gusts, visibility, cloud, temperature. One code worth knowing on sight is CAVOK ("ceiling and visibility OK") — visibility 10 km or more, no cloud below 1,500 m or the minimum sector altitude, and no significant weather. For a drone pilot, CAVOK is as good as the report gets.
A TAF is the forecast: an aviation-grade prediction for an aerodrome covering the next 24–30 hours, issued four times a day at 0000, 0600, 1200, and 1800 UTC. Two of its codes carry most of the meaning. BECMG 1022/1024 29018KT means conditions become the new value during that window and then stay — a lasting change. TEMPO 1012/1014 29018G28KT means temporary fluctuations during that window — gusts to 28 knots arriving in episodes.
The TAF is what turns weather checking from a snapshot into a plan, because a drone flight happens over time. The classic exam scenario is also the classic real one: the mission is set for 11:00, the current METAR is inside limits, but the TAF carries a TEMPO between 10:00 and 12:00 with gusts above the aircraft's rating. The correct call is to move the flight out of the TEMPO window or postpone — the observation says "fine now," the forecast says "not during your window," and the forecast is the one talking about your flight.
In Latvia, METAR and TAF are published for aerodromes such as Rīga (EVRA), and any aviation-weather site or app will retrieve them by ICAO code. Wind-model apps such as Windy or UAV Forecast are useful for the picture between aerodromes — but a general consumer weather app is not an aviation-grade source, and the forecast you check should be for the operating area, not just your launch point.
Temperature works against you at both ends
Heat first. Warm air is less dense, and propellers make lift by working against the air they have. On a hot day the same drone needs higher RPM to hold the same hover, draws more current, drains the battery faster, and has less margin for payload and wind. This is density altitude: the aircraft performs as if it were flying higher than it is. On a 35 °C afternoon the effect is real even at Latvian elevations.
Cold is mostly a battery story — capacity drops sharply and voltage can sag under load, which is how a winter flight ends in an abrupt forced landing. The habits that manage it (warm the pack before take-off, hover to load it gently, expect shorter flights) are covered in the battery-care guide.
The cold trap that is easy to miss is icing on the propellers. It needs two things at once: temperature near or below 0 °C and visible moisture — cloud, mist, freezing drizzle. Clear, dry air at −5 °C will not ice a propeller; damp air at +2 °C over a cool autumn lake just after sunrise can. Ice changes the blade's shape, lift falls, and a small drone has no de-icing system. If the forecast pairs near-zero temperatures with fog, drizzle, or low cloud, that combination is the check that matters.
Clouds that end the flight day
One cloud type gets its own rule. A cumulonimbus (Cb) — the towering thunderstorm cloud, coded CB in METAR cloud groups — produces lightning, violent gusts, and severe turbulence that reach well beyond the cloud itself. The separation rule is 10 km from any active Cb. A cell visible 8 km away is not "still far"; it is already inside the distance at which its outflow can arrive before the rain does. The correct action with footage still on the wish list is to land now.
The afternoon warning sign is watching cumulus clouds grow into towers after a morning of strong sunshine. That signals active thermal convection: sudden turbulence, strong up- and downdrafts, and the possibility that one of those towers matures into a Cb. Rapidly growing clouds are a signal to end the flight, not to hurry it.
The quieter phenomenon is the temperature inversion — warm air sitting on top of cold, common in Latvia on autumn and winter mornings. An inversion traps moist air near the surface, cutting visibility and often producing fog, and the inversion layer acts as a lid under which turbulence concentrates. Morning haze that refuses to lift is an inversion telling you the atmosphere has not opened for business yet.
Visibility is a VLOS requirement, not a comfort
Open-category flying is built on VLOS: the remote pilot must be able to keep the aircraft in unaided sight and judge its position, attitude, and direction continuously. That makes visibility a regulatory input, not a preference. As a practical planning minimum, about 3 km of visibility is where a meaningful VLOS operation starts — below that, you can lose the ability to judge the aircraft's orientation even at short range. METAR reports visibility directly (10 km is the maximum it reports), so the number is one glance away. And on clear days, remember the low sun: a drone downwind of a winter sunset is a black dot in your eyes exactly when you need to read its heading. The VLOS rules and the observer role have their own guide.
The go/no-go call in six questions
Before committing to a flight, the briefing reduces to this:
- Gusts — is the gust figure (not the mean) inside the aircraft's rated wind resistance, with margin?
- Wind aloft — assuming stronger wind at operating height than at the surface, does the plan still hold?
- Trend — does the TAF keep conditions inside limits for the whole window, or is there a TEMPO/BECMG against you?
- Temperature — hot enough for density-altitude margins, or cold and damp enough for battery sag and icing?
- Convection and fog — any Cb within 10 km, towers growing, or an inversion sitting on the morning?
- Visibility — enough to hold genuine VLOS at your planned range, sun position included?
Six honest answers, and the decision usually makes itself. The pre-flight checklist starts with exactly this block — weather is the first gate, before the drone and before the pilot.
Why this is on the exam
For A1/A3, weather appears as an operational duty: the pre-flight assessment must confirm that conditions fit the aircraft and preserve VLOS. The A2 certificate goes further — meteorology is the first of its three exam themes, alongside UAS flight performance and ground-risk mitigation, and the exam (30 questions, 30 minutes, 75 % to pass at CAA Latvia) expects you to decode wind groups, weigh METAR against TAF, and reason about turbulence, density altitude, and icing. That is a skill you can drill: the A2 meteorology mock exam targets this theme question by question, and the A2 certificate guide covers the rest of the path.
Weather is the one variable in drone flying that no checklist can override — it can only be read early and respected. Put the six-question briefing in front of every flight, drill the theme with the A2 meteorology mock exam and the practice sets, and the go/no-go call stops being a feeling and becomes a habit — made at the kitchen table, five minutes into the coffee, exactly where it belongs.
