How Weather Affects Your Flight: Delays, Turbulence, and More

How Weather Disrupts Airport Operations

Weather is the single largest cause of flight delays worldwide, accounting for approximately 70% of all air traffic delays in the United States according to the FAA. Unlike mechanical delays or staffing issues, weather-related disruptions can simultaneously affect hundreds of flights across an entire region, creating cascading effects that ripple through the network for 12–24 hours after the weather itself has cleared. A single major thunderstorm complex over Chicago — a critical hub — can delay or cancel hundreds of flights and affect passengers who never go near Illinois.

The impact of weather on aviation operates through several distinct mechanisms. Reduced visibility limits the types of approaches aircraft can fly and slows the overall throughput rate of busy airports. Low ceilings (cloud base height) prevent visual approaches, forcing all aircraft onto instrument approaches that require greater spacing. Strong crosswinds may make a runway unusable or require reduced weight limits for takeoff. And some weather phenomena — thunderstorms, severe turbulence, icing — create direct safety hazards that require active avoidance.

Weather forecasting for aviation is a specialized discipline conducted by national meteorological services and private aviation weather providers. In the US, the Aviation Weather Center (AWC) issues SIGMETs (Significant Meteorological information) for hazards like severe turbulence, volcanic ash, and tropical cyclones, along with AIRMETs (Airmen's Meteorological Information) for moderate icing, turbulence, and mountain obscuration. These products are consumed by dispatchers and pilots during pre-flight planning to route around significant weather systems.

Thunderstorms: Aviation's Most Dangerous Weather

Thunderstorms are the weather phenomenon pilots and dispatchers fear most. A mature cumulonimbus cloud — the thunderstorm cell — can reach heights of 60,000 feet (18,300 meters), far above any commercial aircraft's ceiling. Within and near thunderstorms, all four of aviation's primary weather hazards coexist: severe turbulence from the violent up and downdrafts (which can exceed 6,000 feet per minute), lightning that can temporarily blind pilots and occasionally damage aircraft systems, hail that can dent leading edges and destroy engines, and windshear that can cause immediate and catastrophic loss of airspeed on approach.

Wind shear — a sudden change in wind speed or direction over a short distance — is particularly dangerous during the approach and landing phase. Microbursts, which are concentrated downdrafts that spread outward when they hit the ground, can cause an aircraft on approach to experience a sudden headwind (increasing lift) followed immediately by a tailwind (decreasing lift) as it flies through the burst. This sequence, happening in seconds, can cause a rapid loss of airspeed and altitude. Several catastrophic accidents in the 1970s and 1980s were caused by microburst wind shear, leading to the development of Terminal Doppler Weather Radar systems now installed at airports in thunderstorm-prone regions and Predictive Wind Shear systems on aircraft.

Airlines routinely deviate around thunderstorm cells by 20–50 nautical miles on each side, adding significant flight time and fuel consumption. On some summer days over the US Midwest or Southeast Asia, massive thunderstorm complexes can block multiple preferred routes simultaneously, forcing aircraft onto significant detours or causing ground stops. Transatlantic flights departing from North America in summer regularly reroute north via Canada or south near Bermuda to avoid convective weather over the primary routing.

Ice and Winter Weather Operations

Aircraft icing is a serious aerodynamic hazard. Ice accumulation on wings changes their profile, reduces lift, increases drag, and adds weight — all simultaneously. Even a thin layer of ice roughness on the leading edge, comparable in thickness to coarse sandpaper, can reduce lift by 30% and increase drag by 40%. In severe icing conditions, ice can accumulate at rates of 1–2 centimeters per minute. All commercial aircraft certified for flight into known icing conditions carry de-icing and anti-icing systems: heated leading edges (engine bleed air or electrically heated mats), pitot heat (keeping the airspeed sensor clear), and windshield heat.

Ground icing is managed through deicing procedures before departure. Deicing fluid — typically Type I, a hot orange-colored glycol mixture — removes existing ice and snow from aircraft surfaces. When precipitation is ongoing, a second treatment of longer-lasting Type IV anti-icing fluid (a thickened green formula) is applied. Type IV fluid provides protection for 30–45 minutes in moderate snowfall, establishing a "holdover time" window within which the aircraft must depart. If the aircraft misses its holdover time — delayed in the queue past the fluid's effectiveness — it must return for another treatment, potentially adding significant delay.

Ground operations in winter require extensive additional procedures. Runways are treated with sand, chemicals (sodium acetate, potassium acetate, or calcium magnesium acetate — chosen for environmental reasons over traditional salt), and plowing to maintain acceptable friction coefficients. Taxiways and aprons are similarly maintained. At airports like Oslo Gardermoen (OSL) or Minneapolis-Saint Paul (MSP) that handle hundreds of winter operations daily, these ground operations become an entire industry, employing fleets of specialized vehicles and demanding precise coordination to keep runways open continuously.

Low Visibility Operations

Fog, low cloud, and heavy precipitation can reduce visibility to near zero, forcing airports to conduct Category II or Category III instrument landing system (ILS) operations — special procedures allowing aircraft to approach and land in conditions where the runway may not be visible until very short final approach or even touchdown. A standard ILS Category I approach requires 550 meters Runway Visual Range (RVR) and a 200-foot decision height. Category III C allows fully automated landings with essentially zero visibility and zero decision height, though very few airports and aircraft are certified to this level.

Low visibility operations come with significant capacity penalties. Standard approach separations of 3 nautical miles increase to 4–5 miles in low visibility because controllers cannot rely on aircraft visual separation and must build in additional buffer for precision. Intersecting runway operations are suspended. The capacity of major hub airports can fall by 40–50% in Category III conditions, creating delays even without any cancellations. London Heathrow's two-runway airport can normally handle 87 movements per hour; in Cat III fog conditions, it may be limited to 50–55.

Winter operations at airports are managed by Airport Meteorological Offices (AMOs) or contracted weather service providers who monitor conditions continuously and update ATIS information in real time. When freezing fog is forecast, airports pre-position deicing equipment, brief additional ground crews, and coordinate with ATC to develop contingency plans. Some airports have invested in computerized weather monitoring systems that track temperature, dew point, and precipitation intensity at multiple points on the airport surface, providing advance warning of developing icing conditions before aircraft are affected.

Turbulence: Causes, Types, and Safety

Turbulence is the irregular motion of air that causes aircraft to shake, bounce, or lurch. While disturbing to passengers, the vast majority of turbulence encountered in commercial aviation is moderate at most and poses no structural risk to well-maintained aircraft. Airlines use PIREPs (Pilot Reports) — real-time reports from flight crews describing turbulence intensity, altitude, and location — alongside forecast products to route aircraft around the worst areas. Modern aircraft are also equipped with weather radar that detects precipitation associated with convective turbulence, allowing pilots to visually navigate around storm cells.

Clear Air Turbulence (CAT) is the most unpredictable form. It occurs at cruise altitude in cloud-free air, often near the jet stream boundaries where air masses of sharply different speeds interact. Because there is no visible cloud or precipitation to detect with weather radar, CAT provides no advance warning. Moderate to severe CAT has caused serious injuries to unbelted passengers and crew — it is the leading cause of non-fatal injuries in commercial aviation. The standard recommendation to keep seatbelts loosely fastened whenever seated remains the most effective protection against unexpected turbulence.

Seasonal weather patterns significantly affect flight operations. The Northern Hemisphere summer brings thunderstorm season across North America, Europe, and Asia, adding delay risk to routes crossing mid-continental weather. Winter brings icing conditions and reduced visibility in northern climates. The monsoon season in South and Southeast Asia (June–September) disrupts operations across a massive geographic region. Airline schedulers build seasonal buffers into schedules and dispatchers file alternate routes and fuel reserves to manage the statistically higher probability of weather disruptions during peak weather seasons.