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Threats & Emergencies  

Winter Weather

Winter Home • Winter Basics • Preparing for Winter Weather • Responding to Winter Weather

Winter Basics

Wind Chill

It is important to understand the concept of wind chill. Wind chill temperatures are often broadcast along with the actual temperatures.

The wind chill temperature indicates the effect of wind on the ambient temperature. Wind chill is based on the rate of heat loss from exposed skin caused by wind and cold. As the wind increases, it draws heat from the body, driving down skin temperature and eventually the internal body temperature. Therefore, the wind makes it feel much colder. If the temperature is zero and the wind is blowing at 15 mph, the wind chill is 19 below zero. At this wind chill temperature, exposed skin can freeze in 30 minutes.

Wind Chill Index

The National Weather Service and Meteorological Services of Canada recently instituted a new Wind Chill Temperature Index, designed to provide a more accurate reading of how the cold air feels on the human skin.

The wind chill index used in the United States and Canada since 1945 relied on observed winds 33 feet above the ground, and focused on how fast the cold temperatures—combined with winds—made water freeze. The new index accounts for wind effects at face level, and a better calculation of body heat loss. For example, under the old index system, a temperature of 20 degrees, with a 15 mph wind, translated into a reading of five degrees below zero. The new wind chill index under the same conditions is six degrees above zero.

The new index is based on:

• Wind speed at the average height of the human face, about five feet (the human face is most often exposed to the cold)
• Updated heat transfer theory, which factors heat loss from the body to its surroundings during cold, windy days
• A consistent standard for skin tissue resistance
• Clear night sky conditions
• A lowered calm wind threshold from four miles to three miles

Wind Chill Temperature Index Chart

Temperature (°F)
10 meter wind (mph)	Calm	40	35	30	25	20	15	10	5	0	-5	-10	-15	-20	-25	-30	-35	-40	-45
	5	36	31	25	19	13	7	1	-5	-11	-16	-22	-28	-34	-40	-46	-52	-57	-63
	10	34	27	21	15	9	3	-4	-10	-16	-22	-28	-35	-41	-47	-53	-59	-66	-72
	15	32	25	19	13	6	0	-7	-13	-19	-26	-32	-39	-45	-51	-58	-64	-71	-77
	20	30	24	17	11	4	-2	-9	-15	-22	-29	-35	-42	-48	-55	-61	-68	-74	-81
	25	29	23	16	9	3	-4	-11	-17	-24	-31	-37	-44	-51	-58	-64	-71	-78	-84
	30	28	22	15	8	1	-5	-12	-19	-26	-33	-39	-46	-53	-60	-67	-73	-80	-87
	35	28	21	14	7	0	-7	-14	-21	-27	-34	-41	-48	-55	-62	-69	-76	-82	-89
	40	27	20	13	6	-1	-8	-15	-22	-29	-36	-43	-50	-57	-64	-71	-78	-84	-91
	45	26	19	12	5	-2	-9	-16	-23	-30	-37	-44	-51	-58	-65	-72	-79	-86	-93
	50	26	19	12	4	-3	-10	-17	-24	-31	-38	-45	-52	-60	-67	-74	-81	-88	-95
	55	25	18	11	4	-3	-11	-18	-25	-32	-39	-46	-54	-61	-68	-75	-82	-89	-97
	60	25	17	10	3	-4	-11	-19	-26	-33	-40	-48	-55	-62	-69	-76	-84	-91	-98
								Frostbite can occur in 15 minutes or less

Wind Chill (°F) = 35.74 + 0.6215T - 35.75(V^0.16) + 0.4275T(V^0.16)

T = Air Temperature (°F) V = 10 meter Wind Speed (mph)