AIRMETs, SIGMETs, and Convective SIGMETs — the in-flight weather advisories that tell you where not to fly

AIRMETs, SIGMETs, and Convective SIGMETs are the three levels of in-flight weather advisories that tell pilots where hazardous conditions exist. They form a hierarchy from least to most severe: AIRMETs warn light aircraft and less experienced pilots, SIGMETs warn all aircraft, and Convective SIGMETs flag dangerous thunderstorm activity. Understanding how to read and act on these advisories is essential for making sharp go/no-go decisions.

What Are the Three Levels of In-Flight Weather Advisories?

When you pull a standard weather briefing — whether through 1800wxbrief.gov, ForeFlight, or Flight Service — you’ll encounter three tiers of advisories:

• AIRMETs (least severe) — hazardous to small aircraft and less experienced pilots
• SIGMETs (moderate) — hazardous to all aircraft
• Convective SIGMETs (most severe) — issued specifically for dangerous thunderstorm activity

The distinction isn’t just about severity. It’s about audience. An AIRMET says small aircraft and less experienced pilots should watch out. A SIGMET says everyone needs to watch out — even airline dispatchers start rerouting flights.

What Are the Three Types of AIRMETs?

AIRMET stands for Airmen’s Meteorological Information. If you’re a student pilot, freshly minted private pilot, or low-time instrument pilot, AIRMETs are talking directly to you. Each type gets a phonetic identifier.

AIRMET Sierra covers IFR conditions and mountain obscuration. Ceilings below 1,000 feet, visibility below 3 miles, or mountains hidden by clouds and fog. For VFR pilots, Sierra covering your route is a major yellow flag. Dig into the TAFs and METARs along your route and check whether the timing overlaps your flight.

AIRMET Tango covers turbulence — moderate turbulence, sustained surface winds of 30 knots or greater, or low-level wind shear. Moderate turbulence in formal aviation weather terms means difficulty maintaining altitude and airspeed, unsecured objects moving around the cabin, and passengers gripping armrests. In a Cessna 172, that’s genuinely uncomfortable and potentially dangerous.

AIRMET Zulu covers moderate icing and freezing levels. If you’re flying a typical training aircraft without known-ice equipment — which is nearly all of them — AIRMET Zulu at your planned altitudes is essentially a no-go for flight into clouds. Full stop.

AIRMETs are valid for six hours and cover areas of at least 3,000 square miles, often half a state or more. That broad coverage means the hazard may not exist everywhere within the area, which is exactly why you cross-reference with TAFs and METARs for your specific airports.

How Should I Use an AIRMET in Flight Planning?

Consider a cross-country from Austin, Texas to Oklahoma City. Your briefing shows AIRMET Tango covering central Texas and southern Oklahoma for moderate turbulence below 8,000 feet. Your planned altitude is 4,500.

This doesn’t automatically mean cancel. It means investigate. Check winds aloft at 3,000, 6,000, and 9,000 feet. If winds at 3,000 are from the south at 15 knots and winds at 6,000 are from the west at 35 knots, that wind shear will bounce you around. Your options: climb higher, depart earlier before daytime heating, or postpone. The AIRMET starts the conversation. You finish it.

What Triggers a SIGMET?

SIGMET stands for Significant Meteorological Information and is issued for weather hazardous to all aircraft, not just small ones. Triggers include:

• Severe icing not associated with thunderstorms
• Severe or extreme turbulence not associated with thunderstorms
• Volcanic ash
• Dust storms or sandstorms lowering visibility below 3 miles

SIGMETs are valid for four hours (volcanic ash SIGMETs can extend longer) and cover even larger areas than AIRMETs. A SIGMET for severe turbulence means even large jets are getting tossed around. In a Piper Cherokee, that’s a hard no.

What Is a Convective SIGMET and Why Is It the Most Serious?

Convective SIGMETs are issued specifically for thunderstorms by the Aviation Weather Center in Kansas City. They’re triggered when any of these conditions exist:

• A line of thunderstorms at least 60 miles long
• Active thunderstorms covering at least 40% of an area of 3,000 square miles or more
• Embedded thunderstorms
• Severe thunderstorms with surface winds exceeding 50 knots, surface hail ¾ inch or greater, or tornadoes

These are valid for only two hours but get reissued frequently as storms move and evolve. The rule for general aviation pilots is unambiguous: you do not fly through convective activity, under it, or near it. A Convective SIGMET should immediately shift your thinking from planning the flight to planning the alternative — go earlier, go later, go around, or stay on the ground.

Demonstrating that you understand a Convective SIGMET and chose not to fly because of one is exactly the aeronautical decision-making the FAA wants to see.

How Do I Read Weather Advisories in a Briefing?

Weather advisories appear as both text and graphical overlays on platforms like 1800wxbrief.gov and electronic flight bag apps. Use both.

The text version provides specifics: advisory type, affected area (using VOR references and state boundaries), valid time, hazard type, and expected conditions. For example: AIRMET Tango Update 2, valid 1600Z–2200Z, moderate turbulence below 12,000 feet over portions of southern Colorado and northern New Mexico.

The graphical version shows the advisory on a map so you can immediately see whether your route passes through it. The graphic gives you the big picture; the text gives you the details.

Who Issues These Advisories and How Often?

All three advisory types are issued by the Aviation Weather Center, part of the National Weather Service. The update cycles differ:

Center Weather Advisories (CWAs) are a related but separate product issued by individual Air Route Traffic Control Centers. CWAs are shorter-term, more localized advisories — valid for up to two hours — that fill gaps between the larger products. They don’t replace SIGMETs or AIRMETs.

What’s a Good Decision-Making Framework for Weather Advisories?

During preflight weather briefing, work through advisories in this order:

First, check for Convective SIGMETs along your route and at your destination during your planned time of flight. If present, start thinking about alternatives immediately.

Second, check for SIGMETs. Severe icing, severe turbulence, and volcanic ash are all potential show-stoppers for general aviation.

Third, check AIRMETs — Sierra, Tango, Zulu. These are yellow flags that may or may not be deal-breakers depending on your experience, equipment, and personal minimums. Cross-reference with TAFs, METARs, PIREPs, and winds aloft.

Fourth, check the outlook. If you’re planning a four-hour cross-country and the outlook calls for conditions that would trigger a SIGMET during your return leg, factor that in now — not when you’re 200 miles from home watching the sky darken.

Weather advisories aren’t pass-fail. A 2,000-hour instrument pilot in a well-equipped Bonanza might look at AIRMET Tango and decide to manage it. A 60-hour private pilot in a 152 should think much harder about the same advisory. Both assessments can be correct — they reflect different pilots with different capabilities.

Key Takeaways

• AIRMETs (Sierra, Tango, Zulu) warn of IFR conditions, turbulence, and icing — primarily a concern for light aircraft and less experienced pilots, valid for 6 hours
• SIGMETs warn of severe conditions hazardous to all aircraft, valid for 4 hours — treat these as potential show-stoppers
• Convective SIGMETs flag dangerous thunderstorm activity, valid for 2 hours — general aviation pilots should not attempt to fly through, under, or near these storms
• Always cross-reference advisories with TAFs, METARs, PIREPs, and winds aloft for specific details along your route
• Reassess weather throughout your flight — advisories can expand or shift after departure, and filing PIREPs when you encounter significant weather makes the system better for everyone