UV Index Program

Changes to UV Index Program in 2004

Environment Canada has renewed its UV Index forecast program in the spring of 2004. The forecast methodology for the UV Index has been improved: it now takes into account elevation and, in part, reflection of UV radiation by snow on the ground, two factors that were not included before. In addition, the scheme to determine the UV Index based on observations from Brewer spectrophotometers has been refined. These changes will result, particularly in the spring, in a forecast UV index that will be somewhat higher than in the past.

Moreover, the criteria used to include the UV Index in public forecasts have been modified. The UV Index is now included in the forecast, rounded off to the nearest whole number (no decimals), whenever it is forecast to be of 3 or more, regardless of the season. This means that under certain conditions the UV Index could appear in winter. This also means that it may not appear on heavily overcast or rainy days during the summer.

Finally, in accordance with international recommendations, the categories of the UV Index are now the following:

• low: 0 to 2  (formerly 0 to 3.9)
• moderate: 3 to 5  (formerly 4 to 6.9)
• high: 6 and 7  (formerly 7 to 8.9)
• very high: 8 to 10  (new category)
• extreme: 11 and higher  (formerly 9 and higher)

Please consult our new table of sun protection actions to know more about how to protect yourself against the sun's UV rays at various values of the UV Index.

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