AIM ¶ 7-1-26 — Thunderstorm Hazards
AIM 7-1-26 explains thunderstorm hazards: turbulence, hail, lightning, and radar echo separation rules every pilot must know for checkride prep.
AIM 7-1-26 outlines the many hazards inside and around thunderstorms: turbulence, hail, rain, snow, lightning, sustained updrafts/downdrafts, and icing. Key takeaways for pilots:
- Visual appearance is not reliable — you cannot judge turbulence or hail severity by looking at the cloud.
- Avoidance distances: stay at least 20 miles from severe thunderstorms; 10 miles from less severe ones. Updrafts and downdrafts extend well beyond the visible cloud.
- Radar shows precipitation, not turbulence. Higher reflectivity correlates with more turbulence and liquid water.
- Never fly between strong or very strong echoes separated by 20–30 miles or less — that gap cannot be considered turbulence-free.
- Beneath the storm: strong outflow winds and severe turbulence are likely, especially when low-level humidity is low (surface to 15,000 ft).
- Lightning risk is highest between −5°C and +5°C, and strikes can occur in clear air near a storm.
- METAR has no "severe" descriptor, but 50 kt winds or ¾-inch hail in the report indicates a severe thunderstorm.
- Radar precipitation intensities are reported as light, moderate, heavy, and extreme.
Operationally: give thunderstorms a wide berth — going around, not through, is the only safe option.
Five FAA-written-style questions. Instant explanations, every answer cites its source — no account needed.
What is the direct cause of all wind?
Q1What minimum distance should you maintain from a severe thunderstorm, and why?
Q2Can radar — airborne or ground-based — be used to detect turbulence inside a thunderstorm?
Q3At what temperature range is the probability of a lightning strike to your aircraft greatest?
The hazards in every thunderstorm — and how far they reach
Every thunderstorm contains turbulence, hail, rain, lightning, icing, and severe up/downdrafts, and AIM ¶7-1-26 (reviewed 2026-06-30) warns there is no useful correlation between a storm’s external appearance and the severity of the turbulence or hail inside it. That is why the FAA gives distances, not looks: avoid a severe storm by 20 miles. The tables below turn the regulation into the numbers a DPE expects you to recite.
What is present in every thunderstorm
| Hazard | What AIM ¶7-1-26 says | Checkride takeaway |
|---|---|---|
| Turbulence | Present throughout; little variation with altitude. Do not minimize turbulence beneath the storm. | Severe turbulence up to 20 miles from a severe storm — you cannot fly "around the edge." |
| Hail | Can be carried well outside the visible cloud in the updraft/anvil. | ¾-inch hail is one of the two severe-thunderstorm criteria. |
| Lightning | Can strike an aircraft flying in the clear near a thunderstorm. | Strikes are most likely between −5 °C and +5 °C. |
| Updrafts & downdrafts | Sustained vertical currents that extend far beyond the visible storm cloud. | The visible cloud is only part of the turbulent system. |
| Icing | Supercooled water makes structural icing a hazard inside the cell. | Pair with the −5 °C/+5 °C lightning band when briefing the climb. |
| Low-level outflow / wind shear | Strong out-flowing winds and severe turbulence beneath the storm, worst when humidity is low from the surface to 15,000 ft. | The gust front can reach the runway before the rain does. |
The numbers AIM ¶7-1-26 gives you
| Rule of thumb | Value | What the AIM actually says |
|---|---|---|
| Avoid a severe thunderstorm by | 20 miles | Severe turbulence can be expected up to 20 miles from severe thunderstorms. |
| Avoid a less-severe storm by | 10 miles | The expected turbulence radius decreases to about 10 miles in less severe storms. |
| Radar echoes 20–30 miles apart | No safe path | No flight path through strong or very strong echoes separated by 20–30 miles or less may be considered free of severe turbulence. |
| Lightning-strike temperature band | −5 °C to +5 °C | Strike probability is greatest where outside air temperature is between −5 °C and +5 °C. |
| Severe-thunderstorm criteria | 50 kt or ¾ in hail | METAR has no "severe" descriptor, but 50-knot surface winds or ¾-inch hail meet the threshold. |
| Weather radar detects | Precipitation only | Radar reflects moderate-to-heavy precipitation — it does not detect turbulence directly. |
“The radar looked clear between the cells” is the wrong answer. AIM ¶7-1-26 is explicit: no flight path through strong or very strong radar echoes separated by 20–30 miles or less may be considered free of severe turbulence — and radar shows precipitation, not turbulence, so a clear gap is not a safe gap.
Thunderstorm hazard FAQ
How far should you avoid a thunderstorm?
Per AIM ¶7-1-26, expect severe turbulence up to 20 miles from a severe thunderstorm, decreasing to about 10 miles in less severe storms. Hail and lightning can extend even farther because the updrafts and downdrafts reach well beyond the visible cloud.
What hazards are present in every thunderstorm?
AIM ¶7-1-26 lists turbulence, hail, rain, snow, lightning, sustained updrafts and downdrafts, and icing as all present in thunderstorms. There is no useful correlation between a storm’s external appearance and the severity of the turbulence or hail inside it.
Does weather radar detect turbulence in a thunderstorm?
No. AIM ¶7-1-26 states that airborne or ground-based weather radar normally reflects areas of moderate-to-heavy precipitation, not turbulence. Frequency and severity of turbulence generally increase with radar reflectivity, but radar cannot show the turbulence itself.
At what temperature are lightning strikes to aircraft most likely?
AIM ¶7-1-26 says the probability of an aircraft lightning strike is greatest at altitudes where the outside air temperature is between −5 °C and +5 °C, and lightning can strike an aircraft flying in the clear in the vicinity of a thunderstorm.
What defines a severe thunderstorm?
A thunderstorm is "severe" when it produces 50-knot (or greater) surface winds or hail at least ¾ inch in diameter. METAR reports have no severe descriptor, but AIM ¶7-1-26 notes those criteria let you recognize one from the reported wind and hail values.