Definitions of codes

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.