AIRMETs SIGMETs and Convective SIGMETs and the three-tier advisory system that tells you where the weather wants to ruin your flight

The three tiers of in-flight weather advisories — AIRMETs, SIGMETs, and Convective SIGMETs — tell pilots where conditions are bad enough to warrant changing a flight plan. They fill the gap between decoded METARs and terminal forecasts by answering a critical question: where, right now, is the weather doing something dangerous? Understanding what each level means and how to act on it is essential for safe cross-country planning and checkride readiness.

Many student pilots treat these advisories as background noise on a weather briefing. That’s a mistake. These products are the Aviation Weather Center telling you, in plain language, that a region of airspace has conditions significantly worse than normal. Ignoring them means risking an encounter your airplane and experience level cannot handle.

What Are AIRMETs and When Should You Worry?

AIRMET stands for Airman’s Meteorological Information. Think of these as the lowest tier of the advisory pyramid. The conditions they describe are not necessarily severe, but they are significant enough to concern all pilots and particularly hazardous to light aircraft and pilots with limited experience. That includes every student, every fresh private pilot, and most experienced pilots in small airplanes.

AIRMETs come in three types: Sierra, Tango, and Zulu.

What Does AIRMET Sierra Mean?

AIRMET Sierra covers IFR conditions and mountain obscuration. When Sierra is active, ceilings below 1,000 feet or visibility below 3 miles are expected or already occurring in a defined area.

For VFR pilots, Sierra demands immediate attention. If your route passes through a Sierra area, evaluate your options: Can you deviate around it? Is there an airport along the route where you can land and wait? Will the conditions clear before you arrive?

Mountain obscuration is the other half of Sierra — clouds and fog are hiding terrain. Flying through areas like the Appalachians or the Rockies under a Sierra advisory with mountain obscuration is not a “be careful” situation. The rocks are invisible.

What Does AIRMET Tango Mean?

AIRMET Tango covers moderate turbulence and sustained surface winds of 30 knots or more.

Moderate turbulence can change your altitude by 15 to 25 feet and cause significant airspeed fluctuations. In a Cessna 172, moderate turbulence is exhausting, degrades navigation accuracy, and makes passengers miserable.

The sustained surface wind component matters for different reasons. 30 knots sustained at the surface means gusty conditions, probable crosswinds beyond what a low-time pilot should attempt, and a landing environment that will test anyone’s skills.

What Does AIRMET Zulu Mean?

AIRMET Zulu covers moderate icing. Unless you are flying a certified known-ice airplane — which most training aircraft are not — any icing advisory is a no-go.

Your Skyhawk doesn’t have deice boots. Your Cherokee doesn’t have a heated windshield. Even a thin glaze of ice changes your wing’s camber, increases your stall speed, and adds weight in places the engineers never intended. When Zulu is active for your altitude range and geographic area, stay out.

How Long Do AIRMETs Last and What Area Do They Cover?

AIRMETs are issued for six-hour periods and can be updated as conditions change. They cover large areas, often entire states or multi-state regions. That breadth means the actual bad weather may be concentrated in a smaller pocket within the advisory area.

You won’t know the precise location from the AIRMET alone. Combine it with METARs, PIREPs, and radar to pinpoint where the worst conditions are.

What Are SIGMETs and How Are They Different from AIRMETs?

SIGMETs — Significant Meteorological Information — sit one level above AIRMETs. These describe conditions potentially hazardous to all aircraft, not just light aircraft. When a SIGMET is issued, airliners and corporate jets are paying attention too.

Non-convective SIGMETs cover:

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

Severe turbulence means altitude changes of more than 25 feet, large airspeed fluctuations, and momentary loss of aircraft control. In a training airplane, severe turbulence is an emergency.

SIGMETs are valid for four hours (volcanic ash SIGMETs extend to six hours). They are more geographically specific than AIRMETs, defining areas with coordinates and altitude ranges. When a SIGMET appears on your briefing, read every word, plot the area, and either go around, go above, go below, or don’t go.

What Are Convective SIGMETs?

Convective SIGMETs sit at the top of the pyramid. Issued by the Aviation Weather Center specifically for thunderstorm activity, these represent the most dangerous weather conditions in the advisory system. Convective weather kills general aviation pilots every year.

A Convective SIGMET is issued when any of these conditions are occurring or expected:

• Severe thunderstorms with surface winds greater than 50 knots
• Hail at the surface ¾ inch or greater
• Tornadoes
• A line of thunderstorms at least 60 miles long with storms affecting 40% or more of that line
• Embedded thunderstorms hidden inside other cloud layers
• An area of thunderstorms covering at least 40% of 3,000 square miles or more

Convective SIGMETs are only valid for two hours because thunderstorms change rapidly. A cell that didn’t exist an hour ago can be producing hail and 60-knot downdrafts now. The short validity period means these products are constantly refreshed during active convective weather.

How Should You Apply These Advisories to a Cross-Country Flight?

Consider a practical scenario: a 200-mile cross-country on a summer afternoon. Your briefing shows an AIRMET Tango for moderate turbulence below 8,000 feet across the first half of the route and a Convective SIGMET for a line of thunderstorms moving across the second half.

The AIRMET Tango is workable. Options include flying at a higher altitude if terrain allows, departing in the cooler morning before convective mixing builds turbulence, or accepting the bumps and briefing passengers accordingly.

The Convective SIGMET is a different situation entirely. Thunderstorms contain severe turbulence, hail, lightning, wind shear, and microbursts. The rule of thumb: stay at least 20 miles from any thunderstorm. If convective activity is widespread enough to trigger a Convective SIGMET, you are not threading the needle between cells. You are delaying, rerouting significantly, or canceling.

How Do Weather Advisories Factor into the Checkride?

The Airman Certification Standards for the Private Pilot certificate include a task on weather information. You must demonstrate that you can obtain, read, and apply weather products to flight planning. That includes identifying adverse conditions from AIRMETs, SIGMETs, and Convective SIGMETs and making go/no-go decisions based on what they tell you.

Examiners are looking for the kind of decision-making that connects a weather advisory to a concrete action — not just recognizing the product, but explaining what you would do about it.

How to Remember the Advisory Hierarchy

• AIRMETs — hazardous to all pilots, especially light aircraft and less experienced pilots
• SIGMETs — hazardous to all aircraft, period
• Convective SIGMETs — the atmosphere is at its most violent

Each level up the pyramid means greater hazard intensity and fewer options.

What Is a Center Weather Advisory (CWA)?

A CWA is issued by Air Route Traffic Control Centers for conditions affecting their airspace right now. CWAs are more localized and more immediate than SIGMETs, filling the gap when conditions deteriorate faster than national products can keep up. If you’re receiving flight following and a controller mentions a CWA, pay close attention.

Where to Find These Products

All in-flight weather advisories are available at aviationweather.gov. They are also included in standard weather briefings through Flight Service (1-800-WX-BRIEF) and online briefing tools. Detailed guidance on interpreting these products can be found in the FAA’s Advisory Circular AC 00-45, Aviation Weather Services.

Key Takeaways

• AIRMETs (Sierra, Tango, Zulu) warn of IFR conditions, moderate turbulence, and moderate icing — hazards that are especially dangerous to light aircraft and low-time pilots
• SIGMETs describe severe icing, severe/extreme turbulence, volcanic ash, and sandstorms that threaten all aircraft regardless of size
• Convective SIGMETs are the highest tier, issued for the most dangerous thunderstorm activity including tornadoes, large hail, and embedded storms
• Never rely on a single advisory product — combine AIRMETs and SIGMETs with METARs, PIREPs, and radar to build the full picture
• The 20-mile rule for thunderstorms is a minimum, and widespread convective activity justifies delaying or canceling a flight entirely