Tennessee's policy is built around a compromise that several states have made and few state so plainly: WBGT is the preferred measurement, but heat index is allowed when a WBGT instrument is not available, and the policy publishes paired thresholds so a school can work from either.
The compromise is pragmatic. It avoids a rule that smaller schools cannot afford to follow. It also puts a real decision in front of every athletic director, because the two columns do not describe the same conditions, and the heat index column will miss situations the WBGT column catches.
TSSAA thresholds, WBGT and heat index
The two columns are the policy's own pairing. They are not a conversion, and they will not always agree about the same afternoon.
| WBGT | Heat index | Activity guidelines |
|---|---|---|
| 82.0 to 86.9°F | Under 95°F | At least three separate rest breaks each hour, minimum 3 minutes each during the workout. |
| 87.0 to 89.9°F | 95 to 99°F | Maximum practice time two hours. All sports: at least four separate rest breaks each hour, minimum 4 minutes each. |
| 90.0 to 92.0°F | 100 to 104°F | Maximum practice time one hour, including the rest breaks. 20 minutes of rest breaks distributed through the hour. No conditioning activities. |
| Above 92.0°F | Above 104°F | No outdoor practice. Practice cannot take place until WBGT is 92.0 or below, or heat index is 104 or below. |
Why the two columns disagree
The heat index uses air temperature and humidity only, and assumes shade with light wind. WBGT adds direct sunlight and actual wind speed. On an open practice field in full sun those two additions are most of the story.
The practical consequence is that the heat index column is most likely to understate risk exactly when risk is highest: a still, cloudless afternoon on turf. Conversely, on a hot but dry and breezy day, the heat index can read alarmingly high while WBGT shows a green condition, which trains people to ignore it.
If your school is working from the heat index column, the single highest-value upgrade available is a WBGT instrument. The policy already prefers it. See WBGT vs heat index for the full comparison.
If you are using the heat index column
Until you have a WBGT device, these adjustments narrow the gap.
Add for full sun
OSHA's own guidance advises adding roughly 15°F to the heat index in direct sunlight. The published figure describes shade.
Watch for calm
A dropping wind in the late afternoon raises real heat strain without moving the heat index at all.
Account for turf
Synthetic turf can run 40 to 60°F above air temperature and radiates into everyone on it. No heat index reflects this.
Trust the athletes
When the number and the athletes disagree, the athletes are the better instrument. Symptoms outrank the chart.
Check what your school is required to use before relying on an app. TSSAA names WBGT as the preferred reading and permits heat index as a fallback where a WBGT instrument is not available. Confirm with your school and the current policy what source is acceptable for your records. Where an on-site instrument is required, the WBGT app is a planning and cross-checking tool rather than the compliance reading.
Warning signs of heat illness
Heat stress shows up before it becomes an emergency. Anyone on site should speak up immediately on any of these:
When in doubt, cool first and call for help. Collapse or confusion in the heat should be treated as possible exertional heat stroke: begin cold-water immersion immediately and call 911. Cooling comes before transport.
WBGT without buying an instrument first
If your program is currently working from the heat index because there is no device in the budget, the app gets you a modelled WBGT today, plus the forecast to plan around. It is not a substitute for an on-site instrument where one is required, but it is a long way better than a shade-assumption heat index.
- Real-time WBGT for your location or any city
- Hourly and 14-day WBGT forecasts to plan ahead
- Color-coded flag levels with mode-specific guidance
- Humidity, wind, sun and cloud cover behind every reading
WBGT is estimated from weather data with the peer-reviewed Liljegren model. Where a policy requires on-site measurement, use the app for planning and as a cross-check alongside your instrument.
Common questions
Does TSSAA require WBGT or heat index?
TSSAA names WBGT as the preferred reading but allows heat index as a fallback where no WBGT instrument is available, publishing paired thresholds for both. WBGT accounts for more environmental factors and should be a school's first choice.
What WBGT stops practice in Tennessee?
Above 92.0°F WBGT, or above a 104°F heat index. Outdoor practice cannot take place until the WBGT falls to 92.0 or below, or the heat index to 104 or below.
What is the practice cap at 91°F WBGT in Tennessee?
One hour maximum, and that hour includes 20 minutes of rest breaks distributed through it. No conditioning activities are permitted at that level.
Why does the heat index column understate risk?
The heat index uses only air temperature and humidity and assumes shade with light wind. It cannot see direct sunlight, a dropped breeze or a hot turf surface, which are the conditions that make an open practice field dangerous.
Can a school use a WBGT app in Tennessee?
The policy prefers WBGT over heat index but you should confirm with your school and the current TSSAA document which sources are acceptable for your records. Where an on-site instrument is required, treat an app as a planning and cross-checking tool.
Related WBGT guides
Know the real heat number
Real-time WBGT, flag levels and forecasts. Free on iPhone.
