A SNOWTAM is the message that tells you what state a runway is actually in when the weather has been at it: how much snow, slush or ice is on the surface, and how good the braking is likely to be. It looks like a wall of codes, but it follows a fixed format built around one idea, the runway split into thirds, each with a condition code.
This is general educational information, not operational, legal, or regulatory advice. Rules differ by authority and change over time. Always verify against current official sources and follow your operator's approved procedures.
What a SNOWTAM is
A SNOWTAM is a special-series NOTAM that reports the surface condition of an aerodrome's movement area when it is affected by snow, ice, slush, standing water, frost or similar contaminants. It is issued in a standardised format, set out in the PANS-AIM (Doc 10066) under the parent ICAO Annex 15 aeronautical-information standards, so a SNOWTAM from one country reads the same way as one from another. Because it is a NOTAM, it sits within the same briefing system as the rest of the NOTAMs you read before a flight, but it carries a specific, weather-driven payload about the surface.
The runway condition code and the thirds
Since the worldwide adoption of the Global Reporting Format (GRF), the heart of a SNOWTAM is the runway condition code (RWYCC), and the key thing to know is that the runway is divided into three thirds, each reported separately. The codes run from 6 down to 0:
- 6 is a dry runway, the best braking;
- the middle values describe progressively more contaminated surfaces with poorer braking;
- 0 is the worst, where braking is essentially nil.
So a runway reported as 5/5/3 means good conditions on the first two thirds and a poorer surface on the last third, read in the direction of the lower runway designator. Our guide to the global reporting format for runway conditions explains how those codes are assessed and what each means for braking and for the crosswind you should accept; this guide is about reading the SNOWTAM that delivers them.
The runway condition section
The runway condition part of a SNOWTAM, group by group, identifies:
- the aerodrome by its location indicator, and the date and time the assessment was made;
- the runway designator, which in a SNOWTAM is always given as the lower number of the pair, so a runway used as 09/27 is reported as
09whichever way the traffic is landing; - the three runway condition codes, one per third;
- the percentage coverage of contaminant on each third;
- the depth of contaminant where relevant;
- the type of contaminant, such as dry snow, wet snow, slush, compacted snow or ice.
Read together, these tell you not just a single number but a picture: how much of each third is covered, how deep, with what, and the resulting condition code. That detail is what feeds an aircraft's landing and take-off performance assessment, which is why the report is so structured.
The situational-awareness section
After the runway condition section comes a situational-awareness section, which carries the wider picture: the state of taxiways and aprons, drifting snow, reduced runway width, snowbanks, or any other hazard on the movement area. It is plain-language and free-format compared with the coded runway section, but it matters, because a runway can read well while a taxiway or apron is treacherous, and drifting snow can change the runway itself between assessments. Reading the situational-awareness section stops you from fixating on the runway codes and missing a hazard on the way to or from it.
How it reaches you, and why the time matters
A SNOWTAM arrives through the AIS and NOTAM system as part of your briefing, and like any surface report it has a shelf life. The condition described is the condition at the assessment time; fresh snow, a thaw, or treatment of the surface can change it quickly, so a new assessment supersedes the old. The assessment time is therefore one of the first things to read and one of the last things to forget: an hour-old SNOWTAM in active snowfall is describing a runway that may no longer exist in that state.
What the contaminant types mean
The condition code summarises the surface, but the type of contaminant the SNOWTAM names is what produced it. The type and the depth are read together against the ICAO runway condition assessment matrix (RCAM) in Annex 14, Volume I, and the ranking it produces is not the intuitive one:
- Frost, a wet surface with no more than 3 mm of water, and dry snow, wet snow or slush no more than 3 mm deep all sit at code 5. Dry snow and wet snow are graded together at a given depth, so wet snow is never treated as worse than dry snow; what moves the code is the depth, not how wet it feels underfoot.
- Compacted snow is code 4 when the outside air temperature is at or below minus 15 degrees C, and code 3 when it is warmer, because cold packed snow gives better braking than packed snow near thawing. Dry or wet snow more than 3 mm deep is also code 3.
- Slush or standing water more than 3 mm deep is code 2, so it is graded worse than compacted snow, and it brings its own hazards of drag and spray on take-off and aquaplaning at speed.
- Ice is code 1. Wet ice, water on top of compacted snow, and dry or wet snow lying on top of ice are code 0, the bottom of the scale.
That is why the SNOWTAM reports the type, the depth and the coverage for each third rather than a bare number: the same depth of two contaminants can give two different codes, the same contaminant at two depths can too, and the type feeds the aircraft's performance assessment directly.
When a SNOWTAM is issued and cancelled
A SNOWTAM is issued when the surface condition changes significantly and is re-issued as conditions change again, so a sequence of them traces the runway through a snow event. It is cancelled when the contaminant is cleared and the runway returns to a normal state, or it lapses after its validity. The practical consequence is that you read the latest SNOWTAM, check its assessment time against the current weather, and treat an older one as superseded. In active snowfall, the gap between when the runway was assessed and when you will land is the number that matters most, because the surface you touch down on is the one at your landing time, not the one in the report.
A worked example
You pull the SNOWTAM for your destination. It identifies the aerodrome and the assessment time, which you note is recent. The runway designator reads 09, the lower number of the 09/27 pair, which is how a SNOWTAM always reports it, and it is from the 09 threshold that the thirds are counted. For that runway it gives condition codes 5/5/3: good on the first two thirds and poorer on the last, so the degraded third is the one down at the 27 end. The contaminant section shows the first two thirds with a thin coverage and the last third reporting compacted snow over a high percentage of its area, which is why its code dropped to 3.
Where that third sits in your landing is the point of reading the designator carefully. If you land on 09 the 3 is your rollout third, at the end where you want the brakes to work. If the wind puts you on 27 the same third is the first one you touch down on, which is a different proposition entirely, and nothing in the report reorders itself to tell you so. You take the code to the global reporting format to understand what a 3 means for your braking and for the crosswind you should accept. Then you read the situational-awareness section, which warns of a snowbank beside the runway and drifting snow on a taxiway, both of which you factor into your taxi plan. Last, you re-check the assessment time against the current weather: snow is still falling, so you treat the report as a snapshot that may worsen and plan accordingly. The block of codes has become a clear picture of a runway that is mostly good but degraded at the 27 end, with hazards beside it and a forecast that could change it.
Common pitfalls
- Reading one code for the whole runway. The report gives three codes, one per third; the worst third often matters most.
- Ignoring the contaminant type and coverage. The code summarises, but the type and percentage tell you why, and feed performance.
- Skipping the situational-awareness section. Taxiways, aprons, snowbanks and drifting snow can be worse than the runway.
- Forgetting the assessment time. Surface conditions change fast; an old SNOWTAM in active weather may no longer be true.
- Reading the thirds in the wrong direction. They run from the lower runway designator, which is the one the SNOWTAM reports, so if you land on the higher-numbered end the three codes are listed back to front relative to your landing roll.
- Ranking the contaminants by intuition. The matrix, not instinct, sets the code: wet snow is never graded worse than dry snow at the same depth, and compacted snow scores better than more than 3 mm of slush.
In Pilot EFB
Pilot EFB is a study and planning companion that keeps your NOTAMs, including SNOWTAMs, and the rest of a briefing in one offline-first place, so a briefing you have already pulled stays readable away from a signal. It helps you read and study the format, but it does not assess the runway, compute your performance, or replace the official report, and pulling a fresh SNOWTAM needs a connection. Pilot EFB is not a certified Electronic Flight Bag, so treat it as a study and planning aid and brief from your official source of record.