The system is operational since April,2008 during the warm months (April-October)The Canadian Fire Weather Index, FWI, developed in the Canadian Forest Service Research Center is used.

Data used (input elements for FWI calculation):

• precipitaion amount for the last 24 hours;
• air temperature;
• air relative humidity;
• wind speed; snow cover presence;
• day duration.

FWI has three sub-indices showing the "dryness" of different types of "fuel". Each of these sub-idices is a complex function of the meteo-elements. Knowing the sub-indices and wind velocity data, two other sub indices are calculated, which evaluate the initial fire kindling and the available "fuel" for the further unfolding of the fire. On their basis the FWI in calculated and it gives an overall assessment of the intensity of fire unfolding (in energy released per unit time per unit length along the fire front line).

Thermal Comfort Index in Our Weather Stations on 19.09.2025 в 21 UTC

The data are from the last observation in the Bulgarian weather stations.

Time in Bulgaria is UTC+2 h in Winter and UTC+3 h in Summer.

The proposed maps show the current or expected feeling of thermal comfort/discomfort of the majority of people. The maps refer to a standard time of day, which corresponds to the classical observation periods at weather stations. For example, 12 UTC (Coordinated Universal Time) corresponds to 14:00 Bulgarian time (15:00 summer time), which is usually close to the warmest hours of the day, and 03 UTC corresponds to 05:00 Bulgarian time (06:00 summer weather) which is usually close to the coldest hours of the day.

Thermal Comfort Classes, Description of the Sensation of Comfort/Discomfort and Recommended Clothing

The table shows the degrees of thermal comfort/discomfort. The categories of comfortable, warm and hot are defined on the basis of the degrees of physiological stress to which the human thermoregulatory system is subjected in the different temperature conditions according to the feels like temperature. The categories for cold are according to the Wind Chill Index.

Clothing Index—Meaning

Felt Temperature

Felt temperature is air temperature in a reference atmospheric environment where a person's sense of thermal comfort/discomfort would be the same as in real weather conditions. The feeling of thermal comfort is calculated using a full numerical model of thermal balance of the body of a "standard" human placed in atmospheric conditions near ground, outdoors, on grass or snow cover, if available. The feeling of thermal comfort/discomfort depends on the morphological parameters of the person - age, sex, height, weight and others, but for general purposes, the parameters of a "standard" person are used here. This is a 35-year-old man, 1.75 m tall, weighing 75 kg, in good health. The felt temperature depends on the work performed by the person and can be calculated at different power. In this case, it is assumed that the "standard" person performs work with applying the power corresponding to walking at a speed of 4 km/h on a horizontal surface. It is assumed that the wind always blows to the side of the direction of walking. The clothing is adapted (summer/winter) so that the "standard" person, if possible, achieves thermal comfort in the specific outdoor weather conditions. To determine the felt temperature, data on meteorological elements in the layer of air near the earth's surface (0–2 m), where the "standard" person is located, are used: air temperature; relative air humidity; wind speed; presence of snow cover. Also used: amount of cloud cover; geographical coordinates and altitude of the place; date and time.