How should pilots avoid and fly around thunderstorms?

Pilots should avoid thunderstorms rather than try to penetrate, overfly or pass beneath them. They plan with forecasts and radar, deviate early—at least 20 nautical miles from severe or intense cells—and give the downwind anvil extra room. If a safe route closes, the correct choices are to turn back, divert, hold clear or land.

In Aviation & Real-World Flying, avoidance—not aircraft strength—is the main defence against convective weather. The aircraft flight manual, operator procedures and applicable regulations always take precedence, but no routine technique makes deliberate thunderstorm penetration safe.

How far should an aircraft stay from a thunderstorm?

Keep at least 20 nautical miles from the nearest edge of a thunderstorm identified as severe or producing an intense radar return. Many operators use 20 NM as their baseline for all significant cells because storm strength and position can change faster than the available weather picture.

Twenty nautical miles is not a protective wall. Use a larger margin for rapidly building storms, strong winds aloft, night or instrument conditions, uncertain radar coverage and extensive anvils. Measure from the cell's edge, not its centre—a mistake we see repeatedly in simulated weather flying.

How do pilots plan a thunderstorm deviation?

A safe deviation starts before take-off and preserves an escape route throughout the flight. Pilots should treat convective forecasts as strategic information and onboard radar as one part of a continuously updated tactical picture.

1. Build the broad weather picture. Review forecasts, convective advisories, radar and satellite imagery, pilot reports, METARs and TAFs. Our guide to decoding thunderstorm signs in a METAR explains indicators such as TS, TSRA, VCTS, CB and TCU.
2. Identify alternatives early. Mark airports, turn-back points and routes around the weather. Pilots must also brief terrain, airspace and route constraints so that a weather diversion does not create a different hazard.
3. Carry enough fuel for a real diversion. A token allowance is inadequate when a line is moving, several aircraft are requesting deviations or an alternate may also be affected.
4. Ask ATC before the cell becomes close. Request a deviation direction and distance while several options remain. If a clearance or vector is unsafe, say unable and propose another course.
5. Keep checking the escape route. Watch cell growth and movement, fuel, terrain, daylight and the route behind the aircraft. Turn away while the exit is still obvious rather than waiting for the planned track to become blocked.

ATC can provide weather information and coordinate route changes, but a controller's vector is not a guarantee of thunderstorm clearance. The pilot in command remains responsible for deciding whether the route is safe.

Which side of a thunderstorm should pilots fly around?

The broad upwind side is generally preferable, provided it offers increasing separation and does not conflict with terrain or airspace. The downwind side deserves extra clearance because wind can carry hail, lightning and anvil precipitation far beyond the main rain shaft.

Do not cross directly ahead of a moving cell simply because the present position looks clear; the storm may reach the crossing point first. If neither side provides a stable route with a clear retreat, turn back or divert rather than squeeze between returns.

Why can weather radar show a false gap?

Weather radar displays reflected precipitation energy, not a simple map of safe and unsafe air. Heavy precipitation can attenuate the beam, leaving a dark area or apparent corridor behind a powerful return even though the radar cannot see through it.

Pilots scan different ranges and tilt settings, compare successive images and avoid treating weak colours as proof of weak turbulence. Hail and severe turbulence may exist outside the strongest return, while some hazardous convection can produce less radar energy than expected.

Datalink radar is for strategic planning, not close-range cell threading. Collection, processing and transmission introduce delay, so the weather can be older than the displayed reception age suggests. Airborne radar, lightning information, visual cues, forecasts and ATC reports are complementary; none should be trusted alone.

Can an aircraft fly over or underneath a thunderstorm?

Flying over or underneath a thunderstorm is not a normal avoidance technique. Passing below exposes the aircraft to severe turbulence, hail, lightning, heavy rain, downdraughts, gust fronts and microbursts even when the ground remains visible.

Overflight is also unreliable because convective tops grow quickly and often exceed the aircraft's practical ceiling. It is acceptable only when the top is positively known, the aircraft can maintain the required vertical margin and approved procedures permit it; lateral avoidance is normally the safer choice.

What changes near take-off and landing?

Pilots should delay departure, discontinue an approach or go around when a cell, gust front or windshear hazard is crossing the flight path. A storm several miles from the runway can still produce a dangerous wind shift or microburst over the airport.

ATIS provides useful airport weather, runway and operational information; our explanation of how pilots use ATIS updates covers what the broadcast contains. It is not a complete convective briefing, and conditions may change between broadcasts. Tower reports, onboard predictive windshear alerts and the operator's windshear limits must also be observed.

What should a pilot do after entering a thunderstorm?

An inadvertent thunderstorm encounter requires the aircraft's published turbulence or windshear procedure, not improvised control inputs. Exact actions differ by type, so pilots should follow the flight manual, checklist and operator guidance.

1. Use the published speed and configuration. Set the specified turbulence-penetration speed or power without abrupt changes. Do not guess a generic speed from another aircraft.
2. Control attitude smoothly. Avoid large control movements and accept reasonable altitude and airspeed excursions rather than aggressively chasing both. Autopilot recommendations vary by aircraft and must come from the approved procedure.
3. Work towards the safest exit. Use known storm geometry and radar without making a steep, high-load turn deep inside the cell. A turn away before entry is far safer than attempting a hurried reversal after penetration.
4. Tell ATC and secure the occupants. Report the encounter, request an immediate deviation and use emergency authority if required. Cabin crew and passengers should be seated and restrained.
5. Follow any windshear escape guidance. A windshear warning is a separate, time-critical event; fly the aircraft's published escape manoeuvre rather than the normal turbulence technique.

How should flight-simulator pilots practise storm avoidance?

Use a simulator to practise early decisions, radar interpretation, ATC deviations, fuel consequences and diversions—not to prove that an aircraft can survive a cell. Weather engines and aircraft radar implementations vary, and some models lack realistic attenuation, hail, turbulence or microbursts.

For the Microsoft simulator, our guide to practising radar tilt and return interpretation in MSFS 2024 explains the useful cockpit workflow. Apply real-world separation margins even when the simulated aeroplane can pass through a storm without convincing damage or loss of control.