Icing Reporting: How Ice Appears in Every Weather Product

Icing reporting is spread across four products, and each one encodes it differently. That is why the same hazard can look like a word, a number, a paragraph or a coloured band depending on where you meet it.

Underneath the four encodings sits one ladder: trace, light, moderate, severe. Once you can see that ladder, the products stop looking unrelated.

The one ladder underneath

Every icing product resolves to the same four steps, and the steps are defined by what your equipment can do about the ice.

Trace is just about visible. It builds no faster than it wears off. It is not a hazard unless you sit in it for an hour or more.

Light can be a problem over an hour. The boots clear it. A change of level or heading solves it.

Moderate means even short exposure is a problem. Ice protection has to be used, and diversion or a level change is called for.

Severe means the build rate beats the equipment. Protection no longer keeps up, so an immediate change of altitude or heading is required.

PIREPs: what a pilot met

A PIREP carries icing in the /IC field, and it is the only product describing ice that actually happened.

The field takes an intensity, usually a type, and often an altitude band. A typical entry reads /IC MOD RIME 060-080: moderate rime ice between 6000 and 8000 feet.

The type words are RIME, CLR for clear, and MIXED. That matters, because clear ice is denser, bonds harder and runs back behind the protected surfaces, so a moderate clear report is worse than a moderate rime one.

NEG means the pilot found no ice. That is a real report and one of the most useful in the whole system.

AIRMET Zulu: the forecast band

Zulu is the civil forecast product for moderate icing, and it does something the others do not.

Alongside the icing warning it publishes the freezing level across the region, whether or not any ice is expected. That number is where the risk begins, so it gives you a floor and an escape target at once.

The advisory text gives an altitude band, such as moderate icing between the freezing level and 16,000 feet. That band is the planning tool: below it you are in above-zero air, above it you are out the top.

Zulu stops at moderate. It never warns of severe ice.

SIGMETs: the severe end

Severe icing is a SIGMET, not an AIRMET, and the split is the whole point.

An AIRMET says some aircraft will find this hazardous. A SIGMET says all of them will. Since severe icing is defined as beating the ice protection, no aircraft is exempt by equipment.

A SIGMET gives an area, a level band and a movement. SEV ICE (FZRA) marks severe icing from freezing rain, which is the worst airframe icing there is.

If a SIGMET covers your route at your levels, that is a routing decision rather than a comfort question.

Military TAFs: icing as a number

A military TAF is the only aerodrome forecast that carries icing directly, and it does it numerically.

The 6-group is six digits. 620105 reads as the icing group, code 2 for light rime icing in cloud, based at 1000 feet, 5000 feet thick.

One digit gives both the type and the intensity. The codes run in blocks of three: 1 to 3 light, 4 to 6 moderate, 7 to 9 severe. Inside each block the order is mixed, then rime in cloud, then clear in precipitation.

Those values come from AFMAN 15-124 Table 1.5, and our decoder reads them as the table writes them.

Reading them together

The four products answer different questions, so a briefing uses them in order.

Start with AIRMET Zulu for the freezing level and the band. That frames everything: it tells you which of your planned levels could hold ice at all.

Then check for a SIGMET. If severe icing is forecast in your band, the plan changes before anything else does.

Then read PIREPs in that block of air. They are the only current information, and a run of negative reports through the band is strong evidence the layer is clean today.

If you are using a military field, read the TAF trailer as well, since it carries its own forecast for that specific aerodrome.

Verdict on icing reporting

Learn the four-step ladder once and every product becomes readable. Trace, light, moderate, severe, defined by what the ice does to your protection rather than by how thick it looks.

Then match the product to the question. Zulu for where ice is possible. SIGMETs for where it is dangerous to everyone. PIREPs for whether it is actually there. And the military 6-group when the forecast is for a specific airfield.

Last updated August 29, 2026