Thunderstorms in METAR and TAF
Updated: 2026-09-27 · First published: 2026-09-27 · About this site
A thunderstorm is the only weather phenomenon that carries every aviation hazard at once — severe turbulence, hail, lightning, heavy rain, low-level wind shear, icing and, under the cell, a downburst that can exceed the climb performance of any aircraft. The codes that report it are short. Reading them well means reading the cloud group, the weather group, the remarks and the TAF as one picture, and then giving the storm the distance it demands.
The codes
| Code | Where | Meaning |
|---|---|---|
| TS | Weather group | Thunderstorm at the aerodrome: thunder heard or lightning seen at the field within the last 15 minutes. No precipitation reaching the observation point. |
| TSRA / TSSN / TSGR / TSGS | Weather group | Thunderstorm with rain / snow / hail / small hail or snow pellets. Prefix − or + gives the precipitation intensity. |
| VCTS | Weather group | Thunderstorm in the vicinity: 8–16 km (US: 5–10 SM) from the aerodrome. |
| CB | Cloud group, e.g. SCT035CB | Cumulonimbus observed. The storm cloud, whether or not it is thundering. |
| TCU | Cloud group, e.g. BKN030TCU | Towering cumulus: strong vertical development, a CB in preparation. |
| SQ | Weather group | Squall: a sudden increase of at least 16 kt to 22 kt or more, lasting at least a minute. Usually the gust front. |
| FC / +FC | Weather group | Funnel cloud / tornado or waterspout. |
| RETS | Recent weather | A thunderstorm occurred in the last hour but not at observation time. |
| TSB1310E1355, LTG DSNT SW, CB DSNT NW | Remarks | Begin/end times, lightning distant to the south-west, CB distant to the north-west. |
Reading a convective METAR
LTAI 271450Z 31015G32KT 270V350 3000 +TSRA BKN012 SCT025CB BKN080 24/21 Q1004 RETS WS ALL RWY
Everything here is the same storm. The wind is 15 gusting 32 from the north-west and swinging 80° — the gust front. Visibility is 3 km in heavy rain. There is a broken layer at 1,200 ft (rain-lowered stratus), scattered cumulonimbus at 2,500 ft and an overcast above. The spread is 3 °C at 24 °C, saturated air. The pressure is 1004, low for the season — the mesolow under the cell. RETS says thunder was also heard in the previous hour. WS ALL RWY says an aircraft or a sensor has already reported shear on the approaches. This is an aerodrome to hold away from for 30 to 45 minutes, and every airport page on this site draws the category, the gust and the CB layer for you so the picture is immediate — see LTAI Antalya, which produces reports like this on autumn afternoons.
The hazards, one by one
- Downburst and microburst. A column of cold air descending from the storm and spreading out at the surface. An aircraft flying through it meets a headwind (airspeed rises, the pilot reduces power and pitches down), then a downdraught, then a tailwind (airspeed collapses) — at 300 ft, with reduced power. Microbursts have produced 50 kt airspeed losses. The defence is to not be there: no approach or departure through or under a cell.
- Hail. Falls from the anvil, up to 10–15 NM downwind of the visible cloud, out of clear air. GR in the report is hail at the ground; the airborne hazard exists whether or not it is reported.
- Turbulence. Severe inside and near the cell, including the clear air beneath the anvil and above the top. The updraught/downdraught boundary inside a mature cell can exceed 3,000 ft/min in each direction.
- Lightning. Rarely structurally dangerous to certified aircraft; frequently damaging to avionics, radomes and pilots' night vision. Strikes are most likely in the temperature band from +5 to −10 °C near the cloud.
- Icing. Supercooled water in vast quantities in the updraught, at temperatures where it freezes instantly on contact. The most severe airframe icing in aviation occurs in cumulonimbus.
- Heavy rain and low ceiling. +RA can take the visibility below 1,000 m and the rain-lowered stratus below 500 ft, turning a VFR approach into an unplanned IFR one.
In the TAF
Thunderstorms appear in TAFs as PROB30 2812/2816 TSRA BKN020CB or TEMPO 2813/2817 TSRA. The forecaster is rarely able to say when in a four-hour window the cell will pass; the probability is confidence that it will, not a duration. For planning:
- Treat PROB30/40 TS as a real possibility for the whole window — many operators require an alternate whose TAF has no TS in the arrival window.
- Expect the actual storm to arrive earlier than a model would suggest on a hot afternoon with a sea breeze, and later on a day with a capping inversion; the meteogram's CAPE and precipitation panels on each airport page show the model's view of the timing.
- Plan fuel for a 45-minute hold. Cells move; airports reopen.
Distance
The figures taught in most air law and meteorology courses: at least 20 NM from a severe or well-developed cell, never beneath the anvil, and no attempt to fly between cells that are less than about 40 NM apart. Airborne weather radar shows the precipitation core, not the turbulence, which extends well beyond it; lightning detection shows the electrical activity, not the hail. The METAR shows one point. Put them together, and when in doubt add distance — a diversion to a field 60 NM away is on the directory, and its own report will tell you whether the storm is heading there too.
Frequently asked questions
What is the difference between TS and VCTS?
TS means a thunderstorm at the aerodrome — thunder heard, or lightning and CB observed at the field. VCTS means one in the vicinity, between 8 and 16 km away (5 to 10 statute miles in the US). VCTS is a warning that the aerodrome may be TS within the hour.
What does TSRA mean versus TS?
TSRA is a thunderstorm with rain at the aerodrome; TS alone is thunder without precipitation reaching the ground at the observation point. +TSRA is a thunderstorm with heavy rain, and TSGR one with hail. The intensity prefix applies to the precipitation, not to the storm.
Can a METAR show CB without TS?
Yes. SCT040CB is cumulonimbus cloud observed, possibly distant; TS is only reported when thunder is heard or lightning seen at the field. A CB in the cloud group without TS in the weather group is a storm that has not arrived, or is dissipating, or is simply out of earshot.
How far should I stay from a thunderstorm?
The widely taught guidance is at least 20 NM from a severe storm and never under the anvil; hail can fall 10 NM or more from the visible cloud, and the gust front can be 10–15 NM ahead of the rain. Flying between two cells closer than about 40 NM apart is discouraged.
Does a TAF forecast lightning?
No. It forecasts the phenomenon (TS, TSRA, TSGR) and the cloud (CB), typically with a PROB30 or PROB40 and a time window. The probability is the forecaster's confidence that a storm will affect the aerodrome in that window, not the fraction of the window it will occupy.
Read next
- How to Read METAR Reports: A Pilot's Guide — Learn to decode a METAR line by line: station, time, wind, visibility, weather, clouds, temperature, QNH and trend. Worked example plus the mistakes that catch pilots out.
- VFR vs IFR Flight Categories Explained — What the four flight categories mean, the exact ceiling and visibility thresholds, how to derive them from a METAR or TAF, and how they differ from flight rules and European colour states.
- How to Read a TAF Forecast — Decode a TAF: validity period, FM, BECMG, TEMPO and PROB groups, what each change group promises, and how to pick the worst period for alternate planning. Worked example included.
- Crosswind Component and Runway Selection — The sine rule, the clock-face shortcut, gust handling and a worked example. How crosswind, headwind and tailwind components decide which runway to use and when to divert.
- QNH, QFE and QNE: Altimeter Settings Explained — What each altimeter setting measures, when to use which, how to convert hPa and inHg, what a wrong setting does to your altitude, and how transition altitude and level work.
- All pilot guides — the full library, 15 articles.
- Airports by country — live METAR and TAF for every reporting station
- World weather rankings from the observation archive