HOW DOES WEATHER
AFFECT FLIGHTS?

What weather matters, and when

Weather affects every phase of flight differently. A pilot's preflight briefing covers each phase in sequence — ground operations, departure, en-route, arrival. The weather that matters at each stage is completely different.

• 🚌Ground operations: wind speed and direction for pushback and taxi, precipitation (rain or snow affecting ramp safety), visibility for ground movement, thunderstorm proximity triggering ramp closures.
• ✈Departure: surface wind and crosswind component against runway heading, low-level wind shear in the climb corridor (0–3,000ft), departing visibility minimums, CAPE and thunderstorm risk in the departure sector.
• 🌐En-route: jet stream position and intensity, clear air turbulence regions, thunderstorm cells and deviation requirements, icing levels, significant weather charts (SIGMETs).
• 🛬Arrival: destination visibility and cloud base against approach minima, crosswind on landing runway, wind shear on final approach, alternate airport weather if destination is marginal.

Weather types and their effects

The pre-flight weather briefing

Every commercial flight is preceded by a formal weather briefing reviewed by the dispatcher (responsible for flight planning) and the captain. The core documents are:

METAR — surface observation

A coded hourly observation of actual conditions at the airport: wind speed and direction, visibility, cloud layers, temperature and dew point, altimeter setting. Updated every hour, with special observations (SPECI) issued when conditions change significantly between hourly reports. The METAR tells you what conditions are right now.

TAF — terminal aerodrome forecast

A 24–30 hour forecast of expected conditions at the airport. Issued four times daily by national met services. The TAF is what the dispatcher uses to assess whether the destination will be acceptable on arrival, and to determine whether a fuel alternate is required. If the TAF shows conditions below landing minima at the estimated arrival time, the flight may not depart.

SIGMET — significant meteorological information

Urgent warnings issued when severe turbulence, severe icing, volcanic ash, or tropical cyclones are present or expected. SIGMETs are issued in real time and expire within 4–6 hours. Pilots receiving a SIGMET for their route will deviate around the affected area or request a different altitude.

Upper winds and temperature forecast

Grid-based forecasts of wind and temperature at multiple flight levels (typically FL050 to FL450 in 5,000ft steps). Used for fuel planning, route optimisation, and jet stream positioning. This is the data that tells a dispatcher whether to route north or south of the jet stream on a transatlantic crossing.

When weather causes a diversion

A diversion happens when the destination becomes unsuitable after departure — either because conditions deteriorate below approach minima, or because the aircraft is holding and burning fuel while waiting for conditions to improve. Every flight carries enough fuel to reach at least one designated alternate airport, selected before departure based on its forecast weather.

The most common diversion weather is fog below CAT I minima at airports without CAT III autoland capability. London City, Edinburgh, and many regional airports regularly divert traffic to better-equipped alternates during autumn fog events. Heathrow, Frankfurt and Charles de Gaulle have CAT III autoland and rarely divert for visibility alone.

Thunderstorms cause diversions less often than fog — aircraft can usually hold or slow down until a fast-moving cell passes. A slow-moving or stationary convective system over the destination is more likely to force a diversion than a typical summer storm.

Weather and flight cancellations

True weather cancellations — where the flight cannot operate at all — are less common than people think. Airlines strongly prefer delays over cancellations because cancellations trigger passenger care obligations and rebooking costs. A flight is typically cancelled for weather when the delay would exceed crew duty hour limits, when weather is forecast to persist for the entire operational window, or when the aircraft cannot be positioned due to upstream weather.

The most cancellation-prone weather events are winter blizzards (where airports physically cannot operate for extended periods), severe convective events that ground entire hub airports, and fog events that persist through the entire morning banking window at capacity-constrained airports.

Frequently asked questions

Can a flight be cancelled due to weather at another airport?

Yes — and this is one of the most frustrating passenger experiences. Your aircraft may be stranded at another airport due to weather, making it unavailable for your flight. Or a crew member may have timed out after a weather delay on their previous sector. Operationally, the weather event that cancelled your flight may have happened 500 miles away and four hours earlier.

How much wind is too much for a flight?

It depends on the direction relative to the runway. Headwinds of almost any speed are fine — they actually help with takeoff and landing performance. Crosswinds are the limiting factor. Most commercial aircraft have demonstrated crosswind limits of 35–38 knots, though airlines often set more conservative operational limits. Tailwinds above about 15 knots on landing are also a concern, as they increase the landing distance required.

Does lightning affect flights?

Lightning strikes on aircraft are more common than most passengers know — a typical commercial aircraft is struck by lightning once or twice per year on average. Modern aircraft are designed to conduct the strike safely around the airframe. What lightning does affect is ground operations — ramp workers must cease outdoor activities when lightning is within a certain distance, causing delays to boarding, baggage loading and pushback.

Is flying in rain dangerous?

Rain alone is not dangerous to a modern commercial aircraft. Heavy rain can temporarily reduce engine performance slightly and affects braking distances on wet runways, both of which are accounted for in performance calculations. The risk associated with precipitation comes from what often accompanies it — thunderstorms, hail, wind shear, or icing at altitude — rather than the rain itself.