Storm Impacting the Northwest U.S.; Fire Weather Conditions in Southern California; Severe Weather in the South

A Pacific storm is bringing areas of low elevation rain, moderate to heavy mountain snow, and high winds to the Northwest. Strong Santa Ana winds and very dry conditions are producing elevated to critical fire weather conditions in southern California. Isolated strong to severe thunderstorms are possible through early Wednesday morning across parts of northeast Texas into western Tennessee. Read More >

The New Improved "Wind Chill Index"

The National Weather Service (NWS) is planning to implement a new Wind Chill Temperature (WCT) index for the 2001/2002 winter season. The reason for the change is to improve upon the current index used by the NWS and the Meteorological Services of Canada (MSC) which is based on the 1945 Siple and Passel Index.

For over a year, there has been discussion within the NWS and MSC about updating the WCT. During the Fall of 2000, a special group - consisting of the National Weather Service, MSC and the International Society of Biometeorology - evaluated the existing wind chill formula and made changes to improve upon it. Chaired by the NWS, the group's goal was to internationally upgrade and standardize the Wind Chill Index.

The new Wind Chill/Temperature Index will make use of advances in meteorology, biometeorology and computer modeling to provide a more accurate, useful formula for calculating the dangers from winter winds and freezing temperatures. In addition, clinical trials have been conducted and the results of those trials have been used to verify and improve the accuracy of the new formula.

Led by the NWS, implementation of the standardized WCT Index will take place throughout the nation and will involve the entire meteorological community and the media - which will play an important role in explaining the index to the general public. In this way, an accurate and consistent measure will be provided to help the public protect itself against the dangers of frostbite and hypothermia. The index will be implemented in Canada and the United States in order to have a consistent WCT Index for North America.

Specifically, the new WCT index:

uses calculated wind speed at an average height of five feet (typical height of a human face) based on readings from the national standard height of 33 feet (typical height of an anemometer);
is based on the latest heat transfer theory, i.e., heat loss from the body to its surroundings, during cold and breezy/windy days;
uses a standard factor for skin tissue and assumes a no sunlight scenario

The new equation, Wind Chill (^oF) = 35.74 + 0.6215T - 35.75(V^0.16) + 0.4275T(V^0.16)

Where, T = Air Temperature (^oF)
V = Wind Speed (mph)

Use the table below, or try our calculator

Temperature (F)

W
i
n
d

S
p
e
e
d

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 occurs in less than 30 minutes

For more details, visit the Office of Climate, Water, and Weather Services.

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Storm Impacting the Northwest U.S.; Fire Weather Conditions in Southern California; Severe Weather in the South

The New Improved Wind Chill Index