Forecasts, Observations and Weather Hazard Decisions

Weather is an operating limit

A remote pilot does not read weather to sound clever. The point is to decide whether the aircraft, crew and site still have enough margin to complete the task and recover safely.

For small RPA, the important weather question is practical: what will the wind, visibility, cloud, rain, temperature and local air movement do to control, endurance, VLOS, separation and workload?

• Go when the forecast, site observations, aircraft limits and crew plan all agree.
• Modify when the work can be reduced, delayed, repositioned or shortened without hiding the risk.
• No-go when control margin, visual line of sight, recovery margin or separation is doubtful.

Build the weather picture in layers

Start broad, then narrow. Use the synoptic situation and forecast products to understand the trend, aviation weather products for the operating area when they are available, and site observations to confirm what is actually happening at launch height.

Airservices NAIPS processes meteorological and NOTAM information for pilot briefings, while the Bureau provides aviation forecasts, observations and warning products. For drone work, those sources should sit beside the operator's own site checks and aircraft limits.

• Trend: is the weather improving, steady or deteriorating?
• Wind: mean wind, gusts, direction shifts and terrain or building effects.
• Visibility: haze, dust, smoke, rain, fog, low cloud and slant visibility.
• Hazards: thunderstorms, fronts, showers, strong thermals, windshear or turbulence.

Translate forecast language into decisions

Forecasts and observations usually describe wind, visibility, cloud, weather and pressure in compact aviation language. The study skill is to translate those details into plain operational meaning before the aircraft leaves the ground.

A TAF or weather briefing might point to a later change, but the job may be planned for the hour before that change arrives. That is not a free pass. If the operation has little reserve, a forecast change near the work window should push the pilot toward a shorter job, earlier landing or delay.

A coded weather report is decoded one group at a time. METAR (actual observation) example from the lesson: METAR YBBN 150530Z 18012KT 9999 FEW030 SCT050 25/18 Q1015 RMK RF00.0/000.0. It reads: Brisbane Airport, 15th at 0530 UTC, wind from 180 degrees at 12 knots, visibility 10 km or more, few cloud (1 to 2 oktas) at 3,000 ft and scattered cloud (3 to 4 oktas) at 5,000 ft above aerodrome level, temperature 25 degrees C, dew point 18 degrees C, QNH 1015 hPa, no rainfall. TAF (forecast) example from the lesson: TAF YMML 150500Z 1506/1606 21014KT 9999 FEW040 SCT100. It reads: Melbourne Airport, issued 15th at 0500 UTC, valid 15th 0600 UTC to 16th 0600 UTC, wind from 210 degrees at 14 knots, visibility 10 km or more, few cloud at 4,000 ft and scattered cloud at 10,000 ft. Each cloud group fills a sky dome divided into eight oktas, with a key: FEW 1 to 2, SCT 3 to 4, BKN 5 to 7, OVC 8 oktas.

• Wind direction and speed tell you launch orientation, drift risk and return-home energy demand.
• Visibility and cloud tell you whether VLOS, obstacle clearance and traffic awareness remain credible.
• Weather groups such as rain, thunderstorms, mist, dust or smoke should be treated as task constraints.
• Changes and temporary conditions matter because drone jobs often operate on small weather margins.

Read the Reading METAR, TAF and NOTAMs transcript

Fog and low cloud can close the site quickly

When temperature and dew point sit close together, the air is near saturation. Fog, mist, low cloud or condensation can form with little warning, especially around dawn, after rain, in low-lying country or near water.

The hazard is not only that the aircraft becomes harder to see. Low visibility also reduces contrast, masks wires and masts, hides terrain cues and makes it harder to judge distance and attitude.

Dawn, side view. A pilot stands on higher ground by the launch pad. The drone takes off and flies out over low ground toward a mast with wires. A gauge shows temperature T falling toward the dew point Td until the spread is small. Fog forms in the low ground along the flight path, hiding the mast and wires and swallowing the drone, while the launch area still looks clear. The line of sight to the drone turns red. As the fog lifts the drone returns and lands. With a wide spread selected, no fog forms. Schematic: no temperatures or distances are shown.

• Be cautious when the temperature-dew point spread is small.
• Look along the actual flight path, not just across the launch area.
• Treat improving visibility as something to confirm, not something to assume.

Inversions can trap haze, smoke and low-level wind

A temperature inversion places warmer air above cooler air near the surface. That stable lid can trap smoke, dust, haze, fog and pollution close to the ground instead of letting it mix upward.

For remote pilots, the practical effect is a visibility and judgement problem. A site may look acceptable nearby while the flight path disappears into a shallow layer of haze, smoke or reduced contrast.

Valley cross-section with a pilot on a ridge and a drone flying low over the valley. A small inset graph shows temperature against height. Normal: temperature falls with height, and smoke from a fire on the valley floor rises and mixes away upward. Inversion: the graph shows warmer air above cooler air near the surface, forming a lid. The smoke rises only to the lid, then spreads sideways and a haze layer builds in the valley. The pilot's surroundings on the ridge stay clear, but the drone's flight path disappears into the haze and the line of sight turns red. Schematic; no temperatures or heights are shown.

• Smoke and haze can reduce contrast before they fully block the view.
• Valleys, basins and sheltered low ground can hold poor visibility longer than exposed ridges.
• If smoke haze is forecast or visible, check current warnings and local authority information before operating.

Thunderstorm outflow and microburst risk are stop-work hazards

Thunderstorms are not just rain clouds. The Bureau describes key storm parts including updrafts, downdrafts and outflow. Cool air flowing away from a downdraft can spread quickly along the ground, often marked by a shelf cloud, dust, sudden wind shift or sharp temperature change.

A microburst or strong downdraft can produce a sudden burst of damaging wind near the surface. For a small RPA, that can overwhelm control margin, blow the aircraft downwind, reduce endurance and make recovery unpredictable.

A 13 second loop in side view, schematic and not to scale. A thunderstorm cloud sits on the right with rain falling beneath it. A crew on the left has a drone hovering near a windsock that hangs limp in calm air. Down arrows inside the rain shaft show the downdraft. At the ground the cold air spreads out, and a dust-laden gust front labelled outflow races left towards the crew, well ahead of the rain, which barely moves. With "Keeps flying" selected, the outflow reaches the drone while it is still in the air: the windsock snaps round, the drone tilts hard and is blown downwind away from the storm and towards the ground, labelled blown downwind. With "Lands early" selected, the pilot sees the gust front coming, the drone lands on its pad before the outflow arrives and is ticked as landed. The still frame shows the outflow hitting the drone that kept flying, with the rain still far away.

• Watch for towering cumulus, cumulonimbus, shelf cloud, virga, dust walls and rapid darkening cloud.
• Treat lightning, thunder, gust fronts, hail, heavy rain and sudden wind shifts as no-go signals.
• Do not wait for rain to reach the launch point before recovering the aircraft.

Read the Weather hazards transcript

Make the decision explicit

A professional weather decision should be traceable. The pilot should be able to say what was checked, what was observed on site, what limit or trigger would stop the job, and when the next weather review will occur.

This is study guidance, not legal advice. Always verify current CASA, Bureau and Airservices information, follow the operator's procedures, and apply the aircraft manufacturer's environmental limits.

• Record the weather sources checked and the time of the check.
• Brief the crew on weather triggers: gusts, visibility, cloud, rain, storm development or smoke.
• Set a review point during the job, especially when the forecast trend is changing.
• Land early when the weather picture starts moving toward the limit.

Practice Questions