Information on Heat Index

The human body contains several mechanisms to maintain its internal operating temperature at 37^oC. When threatened with above normal temperatures, the body will try to dissipate excess heat by varying the rate and depth of blood circulation, by losing water through the skin and sweat glands, and, as a last resort, by panting.

When weather conditions lead to an air temperature above 32^oC and the relative humidity is high, the body does everything it can to maintain its normal temperature. Unfortunately, conditions can exceed the body's ability to cope with the combined affects of heat and humidity. At such times the body may succumb to any of a number of heat disorders including sun stroke, heat cramp, heat exhaustion and heat stroke.

To use the heat index chart below, find the temperature on the left of the chart. Read across until you reach the desired relative humidity. The number which appears at the intersection of the temperature and relative humidity is the heat index.

Note The heat index under direct sunlight will be 8^oC higher than the number shown in the chart.

MDI - Modified Discomfort Indicator

The Modified Distress Indicator indicates the temperature felt. The MDI LED in Weather Display will change colour in accordance with the temperature as follows:

• Black - Extremely hot
• Red - Very Hot
• Yellow - Hot
• Green - Getting warm

When the mouse pointer hovers over the Weather Display LED the temperature and a comment appears.