uv level FORECAST

Forecast updated Wednesday 22nd May 2019


UV LEVEL INDEX

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L - Low - Between 1 & 2
M - Moderate - Between 3 & 5
H - High - Between 6 & 7
VH - Very high Between 8 & 10
E - Extreme 11+


ULSTER

Wednesday 22nd May - H

Thursday 23rd May - M

Friday 24th May - M


MUNSTER

Wednesday 22nd May - H

Thursday 23rd May - M

Friday 24th May - M

CONNACHT

Wednesday 22nd May - H

Thursday 23rd May - M

Friday 24th May - M


LEINSTER

Wednesday 22nd May - H

Thursday 23rd May - M

Friday 24th May - M


UV LEVEL INFORMATION

The ultraviolet index or UV Index is an international standard measurement of the strength of sunburn-producing ultraviolet (UV) radiation at a particular place and time. The scale was developed by Canadian scientists in 1992, then adopted and standardized by the UN's World Health Organization and World Meteorological Organization in 1994. It is primarily used in daily forecasts aimed at the general public, and is increasingly available as an hourly forecast as well.

The UV Index is designed as an open-ended linear scale, directly proportional to the intensity of UV radiation that causes sunburn on human skin. For example, if a light-skinned individual (without sunscreen) begins to sunburn in 30 minutes at UV Index 6, then that individual should expect to sunburn in about 15 minutes at UV Index 12 – twice the UV, twice as fast.

The purpose of the UV Index is to help people effectively protect themselves from UV radiation, which has health benefits in moderation but in excess causes sunburn, skin aging, DNA damage, skin cancer, immunosuppression, and eye damage such as cataracts (see the section Human health-related effects of ultraviolet radiation). Public health organizations recommend that people protect themselves (for example, by applying sunscreen to the skin and wearing a hat and sunglasses) if they spend substantial time outdoors when the UV Index is 3 or higher; see the table below for more-detailed recommendations.

The UV Index is a linear scale, with higher values representing a greater risk of sunburn (which is correlated with other health risks) due to UV exposure. An index of 0 corresponds to zero UV radiation, as is essentially the case at night. An index of 10 corresponds roughly to midday summer sunlight with a clear sky when the UV Index was originally designed; now summertime index values in the teens are common for tropical latitudes, mountainous altitudes, and areas with above-average ozone layer depletion.

While the UV Index can be calculated from a direct measurement of the UV spectral power at a given location, as some inexpensive portable devices are able to approximate, the value given in weather reports is usually a prediction based on a computer model. Although this may be in error (especially when cloud conditions are unexpectedly heavy or light), it is usually within ±1 UV Index unit as that which would be measured.

Typical variation of UV Index by time of day and time of year, based on Fast RT UV Calculator

When the UV Index is presented on a daily basis, it represents UV intensity around the sun's highest point in the day, called solar noon, halfway between sunrise and sunset. This typically occurs between 11:30 and 12:30, or between 12:30 and 13:30 in areas where daylight saving time is being observed. Predictions are made by a computer model that accounts for the effects of sun elevation and distance, stratospheric ozone, cloud conditions, air pollutants, surface albedo, and ground altitude, all of which influence the amount of UV radiation at the surface. The calculations are weighted in favor of the UV wavelengths to which human skin is most sensitive, according to the CIE-standard McKinlay-Diffey erythemal action spectrum. The resulting UV Index cannot be expressed in pure physical units, but is a good indicator of likely sunburn damage.

Because the index scale is linear (and not logarithmic, as is often the case when measuring things such as brightness or sound level), it is reasonable to assume that one hour of exposure at index 5 is approximately equivalent to a half-hour at index 10, although other factors like the body's ability to repair damage over a given time period could detract from the validity of this assumption.