Definitions of codes
Help to understand the codes we use to describe the weather.
Weather types
| Value | Description |
|---|---|
| NA | Not available |
| -1 | Trace rain |
| 0 | Clear night |
| 1 | Sunny day |
| 2 | Partly cloudy (night) |
| 3 | Partly cloudy (day) |
| 4 | Not used |
| 5 | Mist |
| 6 | Fog |
| 7 | Cloudy |
| 8 | Overcast |
| 9 | Light rain shower (night) |
| 10 | Light rain shower (day) |
| 11 | Drizzle |
| 12 | Light rain |
| 13 | Heavy rain shower (night) |
| 14 | Heavy rain shower (day) |
| 15 | Heavy rain |
| 16 | Sleet shower (night) |
| 17 | Sleet shower (day) |
| 18 | Sleet |
| 19 | Hail shower (night) |
| 20 | Hail shower (day) |
| 21 | Hail |
| 22 | Light snow shower (night) |
| 23 | Light snow shower (day) |
| 24 | Light snow |
| 25 | Heavy snow shower (night) |
| 26 | Heavy snow shower (day) |
| 27 | Heavy snow |
| 28 | Thunder shower (night) |
| 29 | Thunder shower (day) |
| 30 | Thunder |
Visibility
| Value | Description |
|---|---|
| UN | Unknown |
| VP | Very poor - Less than 1 km |
| PO | Poor - Between 1-4 km |
| MO | Moderate - Between 4-10 km |
| GO | Good - Between 10-20 km |
| VG | Very good - Between 20-40 km |
| EX | Excellent - More than 40 km |
UV Index
The strength of the sun's ultraviolet (UV) radiation is expressed as a 'Solar UV Index', a system developed by the World Health Organization. These Met Office forecasts include the effects of:
- the position of the sun in the sky;
- forecast cloud cover;
- ozone amounts in the stratosphere.
The solar index does not exceed 8 in the UK (8 is rare; 7 may occur on exceptional days, mostly in the two weeks around the summer solstice). Indices of 9 and 10 are common in the Mediterranean area.
The UV Index can take the following values:
| Value | Description |
|---|---|
| 1-2 | Low exposure. No protection required. You can safely stay outside |
| 3-5 | Moderate exposure. Seek shade during midday hours, cover up and wear sunscreen |
| 6-7 | High exposure. Seek shade during midday hours, cover up and wear sunscreen |
| 8-10 | Very high. Avoid being outside during midday hours. Shirt, sunscreen and hat are essential |
| 11 or over | Extreme. Avoid being outside during midday hours. Shirt, sunscreen and hat essential. |