AIRMETs and SIGMETs are weather advisories issued by the FAA and National Weather Service to warn pilots about hazardous conditions. They are not the same thing and the Part 107 exam will test whether you know the difference. The good news is once someone explains the logic behind them, they are pretty easy to keep straight.
The One-Sentence Version
An AIRMET is a weather advisory for conditions that are hazardous mainly to smaller or less-capable aircraft. A SIGMET is a weather advisory for conditions that are hazardous to all aircraft, including large commercial jets. SIGMETs are the more serious of the two.
Both are issued for a specific geographic area and a specific time window. Both are issued by the Aviation Weather Center. The difference is severity and who they apply to.
What Is an AIRMET?
AIRMET stands for Airmen's Meteorological Information. AIRMETs come in three types, each identified by a letter and a nickname:
| Type | Nickname | What It Covers |
|---|---|---|
| AIRMET Sierra | Sierra = IFR | Instrument Flight Rules conditions — ceilings below 1,000 feet and/or visibility below 3 miles affecting more than 50% of an area. Also includes mountain obscurement. |
| AIRMET Tango | Tango = Turbulence | Moderate turbulence, sustained surface winds of 30 knots or more, or low-level wind shear. |
| AIRMET Zulu | Zulu = Icing | Moderate icing and freezing levels. |
AIRMETs are valid for up to 6 hours, or up to 12 hours for mountain obscurement and icing. They are issued every 6 hours as a routine part of the weather briefing cycle, with updates issued between cycles if conditions change.
What Is a SIGMET?
SIGMET stands for Significant Meteorological Information. SIGMETs cover weather that is severe enough to be hazardous to all aircraft, not just smaller ones. There are two categories:
| Type | What It Covers | Valid For |
|---|---|---|
| Convective SIGMET | Severe thunderstorms, embedded thunderstorms, lines of thunderstorms, areas of widespread thunderstorm activity. Issued for the contiguous US only. | Up to 2 hours |
| Non-convective SIGMET | Severe or extreme turbulence not associated with thunderstorms, severe icing not associated with thunderstorms, widespread dust storms or sandstorms lowering visibility below 3 miles, volcanic ash. | Up to 4 hours (6 hours for volcanic ash or tropical cyclones) |
A Convective SIGMET is issued any time there are severe thunderstorms with surface winds over 50 knots, hail at the surface over 3/4 inch in diameter, or tornadoes. If you see a Convective SIGMET for your area, you are not flying.
Side-by-Side Comparison
| Feature | AIRMET | SIGMET |
|---|---|---|
| Severity | Moderate — hazardous mainly to smaller aircraft | Severe — hazardous to all aircraft |
| Issued how often | Every 6 hours, plus updates | As needed when conditions develop |
| Types | Sierra (IFR), Tango (turbulence), Zulu (icing) | Convective, Non-convective |
| Valid period | Up to 6 hours (12 for some) | Up to 2–4 hours depending on type |
| Coverage area | Large geographic regions | Specific area where hazard exists |
| Go/no-go implication | Evaluate carefully, may still be flyable | Treat as a strong no-go signal |
What Do These Mean for Drone Pilots?
Drones operate at low altitude — under 400 feet AGL — so some of the conditions in these advisories are less relevant than they are for manned aircraft. Severe icing at 15,000 feet does not affect a drone flying at 200 feet. But several conditions do matter directly:
- AIRMET Sierra is the most directly relevant to drone operations. If ceilings are below 1,000 feet and visibility is below 3 miles, you may not be able to legally or safely fly. Check the actual METAR to see current conditions at your location.
- AIRMET Tango for surface winds over 30 knots matters. Most consumer drones have maximum wind resistance well below that. High winds at the surface affect drone stability and control directly.
- Convective SIGMETs mean thunderstorms are nearby or developing. Even if the storm is not directly overhead, fast-moving weather associated with convective activity can arrive quickly and unexpectedly.
The practical takeaway: AIRMETs and SIGMETs are part of a complete pre-flight weather check. You check the METAR for current conditions, the TAF for what is forecast, and any AIRMETs or SIGMETs for broader hazards in the area.
Where to Find Them
Current AIRMETs and SIGMETs are available at the Aviation Weather Center. You can view them as text advisories or as overlays on a map, which makes it easier to see if your flight area is inside an active advisory.
What the Exam Tests
The Part 107 exam is not going to ask you to decode a full AIRMET text. What it tests is whether you know the types and what they cover. The most common exam questions:
- What does AIRMET Sierra describe? (IFR conditions and mountain obscurement)
- What does AIRMET Tango describe? (Moderate turbulence and strong surface winds)
- What does AIRMET Zulu describe? (Moderate icing)
- What is the difference between an AIRMET and a SIGMET? (Severity — SIGMETs are more serious and apply to all aircraft)
- What does a Convective SIGMET indicate? (Severe thunderstorm activity)
Know those five and you will handle every AIRMET and SIGMET question the exam throws at you.
Weather is one of the biggest topics on the Part 107 exam
FAA 107 Prep covers AIRMETs, SIGMETs, METARs, TAFs, and every other weather topic with practice questions and plain English explanations.