AIRMET Sierra, Tango, and Zulu, the Three Preflight Weather Warnings Most Student Pilots Rush Past, and the G-AIRMET Transition That Changed the Briefing in Twenty Twenty-Two

AIRMETs - Sierra, Tango, and Zulu - are weather advisories issued specifically for smaller aircraft, warning of IFR conditions, turbulence, and icing respectively. Many student pilots treat them as a checkbox item in the briefing. They deserve far more attention than that. Understanding what each type means, and using the graphical G-AIRMET product introduced in November 2022, can be the difference between a manageable flight and a serious decision made without complete information.

How Do AIRMETs Fit Into the Aviation Weather Advisory System?

Aviation weather advisories are issued in a hierarchy based on severity and aircraft type.

SIGMETs (Significant Meteorological Information) sit at the top. They cover hazardous weather affecting all aircraft - severe turbulence, severe icing, volcanic ash, widespread dust or sandstorms reducing visibility below 3 statute miles, and tropical cyclones. When a SIGMET is active, it applies regardless of what you’re flying.

Convective SIGMETs are issued specifically for thunderstorm activity: embedded thunderstorms, lines of storms, or areas of thunderstorm coverage exceeding 3,000 square miles. They’re issued as needed, any time of day, and are valid for no more than two hours.

AIRMETs (Airmen’s Meteorological Information) are one level below SIGMETs in severity. They’re aimed at smaller aircraft - single-engine trainers, light twins, and VFR pilots who need to know that significant weather conditions are widespread and real, not isolated to one airport.

What Does AIRMET Sierra Mean?

Sierra covers IFR conditions and mountain obscuration.

An AIRMET Sierra is issued when ceilings below 1,000 feet AGL, visibility below 3 statute miles, or both are affecting or expected to affect at least 50 percent of the described area. That 50 percent threshold is important: a Sierra doesn’t get issued because one airport in a region has gone IFR. It means the IFR conditions are widespread.

If Sierra is plotted on your route, looking for a clear corridor through it is not a realistic strategy. The advisory describes a region where most of the airspace already meets the criteria.

Mountain obscuration works differently. It doesn’t require a specific ceiling or visibility number. It’s issued when mountains, ridges, or significant terrain are obscured by clouds, precipitation, or fog to a degree that makes VFR flight hazardous. A Sierra for mountain obscuration on your route isn’t a “check it again before departure” situation - it’s a serious alternate-route planning situation.

What Does AIRMET Tango Cover?

Tango covers turbulence, strong surface winds, and low-level wind shear. There are three distinct conditions that trigger a Tango advisory, and all three matter.

Moderate turbulence at or below 18,000 feet MSL, not associated with thunderstorms. This includes mountain wave turbulence, clear air turbulence from jet stream interactions, and frontal turbulence. It won’t damage a light aircraft’s airframe, but it will be fatiguing, uncomfortable, and dangerous if passengers or unsecured items aren’t properly prepared.

Sustained surface winds of 30 knots or more. This surprises students who think of Tango as a high-altitude product. A Tango advisory for surface winds is relevant from cruise altitude all the way to the runway. 30 knots sustained is enough to push a trainer around on final approach and cause weathervaning on rollout.

Non-convective low-level wind shear at or below 2,000 feet AGL. Wind shear in the approach and departure environment can turn a stabilized approach unstable in seconds. The Tango advisory won’t give you exact shear values, but if one is active in your area with low-level wind shear listed as the cause, consult a weather briefer or Flight Service before departing.

What Does AIRMET Zulu Warn About?

Zulu covers moderate icing at or below 18,000 feet MSL, and always includes current and forecast freezing level information.

Moderate icing in the AIRMET sense does not mean light, inconvenient ice. It means ice accumulating at a rate that requires deice or anti-ice equipment to work hard to keep up. For a training aircraft with no ice protection - which describes most aircraft flown during primary training - moderate icing is a no-go condition, full stop.

The freezing level information in a Zulu advisory is useful even when icing isn’t your primary concern. It tells you where moisture in the atmosphere starts behaving differently, informs performance calculations at altitude, and reveals whether clouds near the top of your climb are likely to be above or below freezing. Read that line regardless of whether an icing hazard is active.

What Changed with the G-AIRMET in November 2022?

Before November 2022, AIRMETs were issued primarily as text products. Briefers read them verbally, and the written form consisted of paragraphs of coded location descriptors, VOR radials, and lat/lon coordinates defining the affected polygon. They were valid for six-hour periods, issued four times daily.

The graphical G-AIRMET (G for Graphical) began as a supplement to text AIRMETs, developed by the Aviation Weather Center to make geographic coverage visually intuitive. In November 2022, the Aviation Weather Center officially retired the legacy text AIRMET format. The G-AIRMET is now the official product.

Two practical upgrades came with the transition.

Forecast resolution. The G-AIRMET is still issued four times daily, but each issuance provides forecast snapshots at 0, 3, 6, 9, and 12 hours. Instead of a single six-hour block where you assume worst-case conditions throughout, you get five snapshots across a twelve-hour lookahead. A Sierra covering your destination at issuance time might be forecast to lift before your planned arrival. A Tango clear of your route now might be forecast to migrate onto it during your cruise phase.

EFB integration. Because it’s graphical, the G-AIRMET integrates directly with electronic flight bag apps like ForeFlight and Garmin Pilot. Active advisories overlay directly on your moving map, making it immediately visible whether your route intersects a Sierra or Zulu polygon. That spatial clarity was not achievable with the old text format.

How Should You Actually Use AIRMETs in Your Preflight Briefing?

The wrong approach: note that an AIRMET exists somewhere, confirm it’s not directly on your route, and move on.

The right approach: open the G-AIRMET map on aviationweather.gov or in your EFB, trace your route against all active advisories, and check the forecast snapshots for both your planned departure time and your planned arrival time.

A practical example: you’re flying a Cessna 172 on a 200-mile cross-country in the Midwest, departing around 11:00 AM local, cruising at 7,500 feet MSL.

Your briefing shows a Tango advisory for moderate turbulence between 6,000 and 12,000 feet MSL covering the central part of the state - your route. You’re inside that altitude band. Now you dig deeper: what do the three-hour snapshots show? Is the turbulence forecast to persist or weaken? Is the source frontal lift, a temperature inversion, or mountain wave? Could you fly at 4,000 feet to stay below it?

Your briefing also shows no active Zulu for moderate icing, but the freezing level is at 8,000 feet MSL. At your planned 7,500, you’re close. If you deviate up to 9,000 for terrain or traffic and encounter cloud, you could be above freezing in moist air. That’s not a no-go, but it’s a factor you’re now aware of and can account for.

That’s how AIRMETs inform a decision - not as documentation that you looked at them, but as data that shapes how you fly.

Pay attention to altitude ranges. A Tango advisory for turbulence between 8,000 and 14,000 feet MSL isn’t relevant if you’re cruising at 4,500. But if you were planning to climb higher for a favorable wind, you now have a specific reason to stay low.

What’s the Difference Between an AIRMET and a SIGMET for Icing?

This distinction comes up consistently on checkride orals.

AIRMET Zulu covers moderate icing. Moderate icing means the rate of accumulation may create a problem if flight is prolonged, and deice or anti-ice equipment reduces or controls the hazard.

A SIGMET for icing covers severe icing. Severe icing means the rate of accumulation is such that deice or anti-ice equipment fails to reduce or eliminate the hazard.

For a training aircraft with no ice protection, both are off-limits. But knowing the distinction demonstrates an understanding of the system - not just the vocabulary - which is exactly what a practical test examiner is looking for.

One more detail to have cold: AIRMETs are valid for six hours from issuance. The G-AIRMET provides forecast snapshots every three hours within each issuance’s twelve-hour outlook, but the advisory itself is a six-hour product. If asked on an oral how long an AIRMET is valid, the answer is six hours.

Key Takeaways

• Sierra = IFR conditions (ceilings below 1,000 feet and/or visibility below 3 SM affecting 50%+ of the area) and mountain obscuration
• Tango = moderate turbulence (non-convective, at or below 18,000 feet MSL), sustained surface winds of 30 knots or more, and non-convective low-level wind shear at or below 2,000 feet AGL
• Zulu = moderate icing at or below 18,000 feet MSL, always paired with current and forecast freezing level data
• In November 2022, the Aviation Weather Center retired legacy text AIRMETs; the G-AIRMET is now the official product, offering five forecast snapshots per issuance across a 12-hour lookahead
• AIRMETs are valid for six hours from issuance; check the graphical product at aviationweather.gov or in your EFB and match active advisories against your route and planned cruise altitude, not just your departure airport