National Weather Service United States Department of Commerce

Wet Bulb Globe Temperature

The Wet Bulb Globe Temperature (WBGT) is an indicator of heat related stress on the human body at work (or play) in direct sunlight. It takes into account multiple atmospheric variables, including: temperature, humidity, wind speed, sun angle, and cloud cover. Why is it called WBGT? This differs from heat index. Military agencies, OSHA, activities associations and many others use the WBGT as a guide to managing workload or activity level. 

Click here to find a forecast for WBGT on a national scale - use the drop down menu to select Wet Bulb Globe Temperature.

 

Wet Bulb Globe Temperatures by County
 
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General Thresholds for Wet Bulb Globe Temperature
(click for larger image)

General Thresholds for Wet Bulb Globe Temperature

Kansas State High School Activities Association Thresholds for Wet Bulb Globe Temperature
(click for larger image)

Kansas State High School Activities Association Thresholds for Web Bulb Glob Temperature


 

Forecast Wet Bulb Globe Temperature Maps

Hourly Wet Bulb Globe Temperatures (next 12 hours)
Wet Bulb Globe Temperature This Hour
Latest Run
Wet Bulb Globe Temperature +2 Hours
+2 Hours
Wet Bulb Globe Temperature +4 Hours
+4 Hours
Wet Bulb Globe Temperature +6 Hours
+6 Hours
Wet Bulb Globe Temperature +8 Hours
+8 Hours
Wet Bulb Globe Temperature +10 Hours
+10 Hours
Wet Bulb Globe Temperature +12 Hours
+12 Hours

Daily Maximum Wet Bulb Globe Temperatures
Maximum Wet Bulb Globe Temperature Today
Max Today
Maximum Wet Bulb Globe Temperature Day 2
Max Day 2
Maximum Wet Bulb Globe Temperature Day 3
Max Day 3
Maximum Wet Bulb Globe Temperature Day 4
Max Day 4
Maximum Wet Bulb Globe Temperature Day 5
Max Day 5
Maximum Wet Bulb Globe Temperature Day 6
Max Day 6
Maximum Wet Bulb Globe Temperature Day 7
Max Day 7


 


 

General Thresholds for Wet Bulb Globe Temperature
(click for larger image)

General Thresholds for Wet Bulb Globe Temperature

Kansas State High School Activities Association Thresholds for Wet Bulb Globe Temperature
(click for larger image)

Kansas State High School Activities Association Thresholds for Web Bulb Globe Temperature


 

 
 
 
Initial values are estimates
for the selected location
adjust sliders as needed
Month:
 
 
Day:
 
 
Latitude:
 
 
Fcst Max Temp(F):
80
 
DewPoint(F):
70
 
RH(%):
 
 
Wind Speed(mph):
 
 
Cloud Cover(%):
 
 

HeatIndex(F):
88
 
WBGT(F):
88
 

Map, calculator courtesy National Weather Service - Tulsa, OK


 


 

General Thresholds for Wet Bulb Globe Temperature
(click for larger image)

General Thresholds for Wet Bulb Globe Temperature

Kansas State High School Activities Association Thresholds for Wet Bulb Globe Temperature
(click for larger image)

Kansas State High School Activities Association Thresholds for Web Bulb Glob Temperature


 

Wet Bulb Globe Temperature vs Heat Index

While the WBGT and Heat Index both attempt to describe how "hot" it is and the potential for heat related stresses, they go about it in different ways.

Bottom-line upfront >>>> what value should you use? For day-to-day activities, heat index will serve you well. If you work outside or plan on any sort of vigorous outdoor activity in the full sun, use the WBGT.  

► Heat Index is more commonly used and understood by the general public - the higher the values the hotter it's going to feel and the higher the threat for heat related illnesses. It's calculated from the temperature and relative humidity. What's not commonly known is that Heat Index assumes you are in the shade

► WBGT also uses the temperature and humidity in its calculation, but temperatures are measured in direct sunshine. It also factors in wind speed, sun angle and cloud cover.  

 

Comparing WBGT and Heat Index

 

Examples
Temp F Dew Point F RH % Sky % Wind mph Heat Index F WBGT F
90 65 42 05 03 92 89
90 65 42 05 13 92 83
90 65 42 65 13 92 81
90 70 52 10 06 96 88
90 70 52 60 06 96 86
90 70 52 60 13 96 85
100 70 39 10 13 108 90
100 70 39 10 5 108 94
100 70 39 65 05 108 91

 

WGBT   Heat Index

Origins:

The WBGT date back to the 1950s specifically the United States Marine Corp Recruit Depot on Parris Island, SC. Recruits were required to perform high intensity exercise in a high humidity, high temperature environment. Many soldiers succumbed to heat related illness. In response, a joint effort between the Department of the Navy and Army doctors studied the effects of heat on exercise performance. The result was the WBGT.

WGBT uses several atmospheric variables for its calculations: temperature, humidity, wind speed, sun angle, and cloud cover. Temperatures are measured in the sunlight.

The military uses the WBGT to gauge the potential for heat related stresses to this day. OSHA uses the WBGT as a guide to managing workload in direct sunlight as do athletic departments (college and high school) and other events involving strenuous work or activity. If you work or exercise in direct sunlight, this is a good element to monitor.

Origins:

The Heat Index is based on work carried out by Robert G. Steadman in 1979 ("An Assessment of Sultriness, Parts I and II") where he discussed factors that would impact how hot a person would feel under certain conditions. It incorporates 21 parameters and assumptions: body mass (147.7 lbs), height (5'7"), actively walking (3.1 mph), clothing (pants and short sleeve shirt), heat tolerance, in the shade, etc. This formula became the "heat index". It is the traditional measurement of heat stress due to high temperatures and high humidity.

It is important to note that the heat index is calculated for shady areas. Direct sunlight can add as much as 15 degrees to the heat index

Inputs:
  • Temperature (in sun)
  • Relative Humidity
  • Wind speed
  • Cloud cover
  • Sun angle
Inputs:
  • Temperature (in shade)
  • Relative Humidity

Assumptions:

  • Body mass (147.7 lbs)
  • Height (5'7")
  • Actively walking (3.1 mph)
  • Clothing (pants and short sleeve shirt)
  • Sunlight and UV exposure
  • Heat tolerance

Equation:

WBGT=0.7Tw+0.2Tg+0.1Td
  • Tw = Natural wet-bulb temperature (combined with dry-bulb temperature indicates humidity)
  • Tg = Globe thermometer temperature (measured with a globe thermometer, also known as a black globe thermometer)
  • Td = Dry-bulb temperature (actual air temperature)

For more information on WBGT:

Equation:

Heat Index = -42.379 + 2.04901523T + 10.14333127R – 0.22475541TR – 6.83783(10-3T2) – 5.481717(10-2R2) + 1.22874(10-3T2R) + 8.5282(10-2TR2) – 1.99(10-6T2R2)
  • T = ambient dry temperature (in Fahrenheit)
  • R = relative humidity (percentage)

For more information on the heat index:


 


 

General Thresholds for Wet Bulb Globe Temperature
(click for larger image)

General Thresholds for Wet Bulb Globe Temperature

Kansas State High School Activities Association Thresholds for Wet Bulb Globe Temperature
(click for larger image)

Kansas State High School Activities Association Thresholds for Web Bulb Glob Temperature


 

PREPARE - SAFETY - RESOURCES

Preparedness & Safety Measures for Heat Stress

Before:

  • Reschedule or postpone outdoor plans during peak heating of the day (usually mid to late afternoon).
  • Wear a hat and light weight, light fitting, light colored clothes.
  • Plan to take frequent breaks in shady areas.
  • Check in with family members, friends. Make sure they have a way to keep cool and take necessary precautions from the heat. The elderly and children are especially susceptible to the heat. 
  • Don't forget your pets! Make sure they have adequate shelter (preferably indoors, air conditioned) and ample water. 

During:

  • Take frequent breaks in the shade or in an air conditioned location. Strenuous outdoor activities should be reduced (or eliminated) especially in direct sunlight where there is little ventilation.
  • Drink plenty of water or other non-alcohol fluids. Stay hydrated by drinking plenty of fluids even if you do not feel thirsty. Avoid drinks with caffeine or alcohol.
  • Continue to check on family, friends and your pets. 
  • Don’t get too much sun. Sunburn makes the job of heat dissipation that much more difficult.

 

Resources


 


 

General Thresholds for Wet Bulb Globe Temperature
(click for larger image)

General Thresholds for Wet Bulb Globe Temperature

Kansas State High School Activities Association Thresholds for Wet Bulb Globe Temperature
(click for larger image)

Kansas State High School Activities Association Thresholds for Web Bulb Glob Temperature


 

 

 

 
Suggested Actions and Impact Prevention
Effects
Precautionary Actions
   
Working or exercising in direct sunlight will stress your body after 45 minutes. Take at least 15 minutes of breaks each hour if working or exercising in direct sunlight.
Working or exercising in direct sunlight will stress your body after 30 minutes. Take at least 30 minutes of breaks each hour if working or exercising in direct sunlight.
Working or exercising in direct sunlight will stress your body after 20 minutes. Take at least 40 minutes of breaks each hour if working or exercising in direct sunlight.
Working or exercising in direct sunlight will stress your body after 15 minutes. Take at least 45 minutes of breaks each hour if working or exercising in direct sunlight.