Site Ratings

Location Attributes

WOW lets you provide details about a number of attributes that help other WOW users and the Met Office understand the surrounding environment. These attributes have been compiled based on site grading schemes used by the Climatological Observers Link (COL), the World Meteorological Organisation (WMO) and the Met Office.

These Location Attributes are used to calculate a Site's Rating

Exposure
  • 5: Very open exposure: no obstructions within 10h or more of temperature or rainfall instruments.
  • 4: Open exposure: most obstructions/heated buildings 5h or from temperature or rainfall instruments, none within 2h.
  • 3: Standard exposure: no significant obstructions or heated buildings within 2h of temperature or rainfall instruments.
  • 2: Restricted exposure: most obstructions/heated buildings >2h from temperature or rainfall instruments, none within 1h.
  • 1: Sheltered exposure: significant obstructions or heated buildings within 1h of temperature or rainfall instruments.
  • 0: Very sheltered exposure: site obstructions or sensor exposure severely limit exposure to sunshine, wind, rainfall.
  • R: Rooftop site: Rooftop sites for temperature and rainfall sensors should be avoided where possible.
  • T: Traffic site: equipment sited adjacent to public highway.
  • U: Exposure unknown or not stated.

Exposure ratings relate to the site of the temperature and rainfall instruments only, which should ideally be at ground level. Sensors for sunshine, wind speed etc are best exposed as freely as possible, and rooftop or mast mountings are usually preferable.

Exposure guidelines are based on a multiple of the height h of the obstruction above the sensor height; the standard is a minimum distance of twice the height (2h). Thus for a raingauge at 30 cm above ground, a building 5 m high should be at least 9.4 m distant (5 m less 0.3 m, x 2), and a 10 m building should be at least 17 m from a thermometer screen (10 m less 1.5 m, x2)

Measurements of air temperature
  • A: Standard instruments in Stevenson Screen, calibration within last 10 yr, site exposure minimum rating=3.
  • B: Standard instruments in Stevenson Screen or manufacturer supplied AWS radiation screen, calibration within last 10 yr, site exposure = 2 or 3.
  • C: Standard instruments in Stevenson Screen or manufacturer supplied AWS radiation screen, site exposure 1 or less.
  • D: Non-standard instruments and/or no or non-standard radiation screen and/or sheltered site, site exposure 1 or less.
  • U: Instruments unknown or not stated.
  • 0: No air temperature measurements made at this site.

STANDARD INSTRUMENTS in this context means: Calibrated mercury-in-glass thermometers or calibrated electronic temperature sensors.

Measurements of rainfall
  • A: Standard ''five inch'' manually-read raingauge or calibrated tipping-bucket raingauge, at standard height above ground (30 cm), site exposure minimum = 3.
  • B: Standard ''five inch'' manually-read raingauge or calibrated tipping-bucket raingauge, the rim mounted at standard height above ground (30 cm), exposure = 2 or 3.
  • C: Standard ''five inch'' manually-read raingauge or calibrated tipping-bucket raingauge, the rim mounted at standard height above ground (30 cm), exposure 1 or less.
  • D: Non-standard raingauge and/or tipping-bucket raingauge, exposure 1 or less.
  • U: Instruments unknown or not stated.
  • 0: No rainfall measurements made at this site.

STANDARD INSTRUMENTS in this context means: Standard-pattern (Snowdon or Met Office Mk II pattern) ''five-inch'' copper raingauge, with deep funnel, the rim of the gauge level and mounted at 30 cm above ground level, meeting the minimum exposure requirement of being at least 'twice the height'' of the obstacle away from the obstacle.

Measurements of wind
  • A: Wind sensors calibrated within last 10 years, mounted 10m above the ground on mast or pole, with no obstructions within 100m.
  • B: Wind sensors mounted above the ground on mast or pole, with no obstructions within 50m.
  • C: Wind sensors mounted on building or wall.
  • U: Instruments unknown or not stated.
  • 0: No wind measurements made at this site.
Urban Climate Zone Index (UCZ)
  • 1: Intensely developed urban zone with detached close-set high-rise buildings with cladding, e.g. downtown towers.
  • 2: Intensely developed high density urban with 2 - 5 storey, attached or very close-set buildings often of brick or stone, e.g. old city core.
  • 3: Highly developed, medium density urban with row or detached but close-set houses, stores & apartments e.g. urban housing
  • 4: Highly developed, low density urban with large low buildings & paved parking, e.g. shopping mall, warehouses.
  • 5: Medium development, low density suburban with 1 or 2 storey houses, e.g. suburban housing.
  • 6: Mixed use with large buildings in open landscape, e.g. institutions such as a hospital, university, airport.
  • 7: Semi-rural development with scattered houses in natural or agricultural area, e.g. farms, estates.
  • U: UCZ unknown or not stated.

UCZ descriptions as defined by the World Meteorological Organisation (WMO-No.8, 8th Edition)

Reporting hours
  • A: Will always aim to provide a weather report at 09:00 GMT. Daily temperature and rainfall values relate to standard 24 hour period morning to morning.
  • B: Will always aim to provide a weather report between 06:00 and 09:00 GMT. Daily temperature and rainfall values relate to standard 24 hour period morning to morning.
  • C: Daily temperature and rainfall values relate to the 24 hour period midnight to midnight. This is the default for most automatic weather stations.
  • D: Air temperature and rainfall terminal hour is other than A, B or C above, or extremes do not relate to 24 hour periods.
  • U: Reporting hours unknown or not stated.
How site ratings are calculated

Each site is automatically allocated a 'site rating'' based on the observing location attributes entries submitted on site registration. The system is based on the quality and exposure of the temperature and rainfall data:

5* = E5, T=A, R=A
4* = E >= 3, T=A, R=A
3* = E >= 3, T[=A,B or C], R[=A,B or C]
2* = E >= 1, T[=Any], R[=Any]
1* = E =0,1,R or U, T[=Any], R[=Any]

(Where E = Exposure, T = Temperature, and R = Rainfall, and each of these are described in Location Attributes).

If temperature is measured at a site, but not rainfall, the site rating will be based on the quality and exposure of the temperature data alone. If rainfall is measured at a site, but not temperature, the site rating will be based on the quality and exposure of the rainfall data alone.

If there is no temperature or rainfall data, the site will be classed as 1*