Teaching · For Teachers · Earth science

What the air
actually feels like,
reading by reading.

Log temperature, wind and humidity from your schoolyard or a forecast. The calculator applies the same formulas the National Weather Service uses, says which one fits each reading, and names the risk category.

Log a readingWhat you get

The feels-like calculator

The worked example is made up: four readings a class might take on a January bus stop and a June track. Replace them with your own. Nothing you type leaves this browser.

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What you get

Teaching · For TeachersFree

What you finish with
A log of weather readings, each with the wind chill or heat index from the National Weather Service formulas, the formula that applied and the NWS category, plus the coldest and warmest feels-like values. It prints as a class log and downloads as a spreadsheet for graphing.
Who it is for
Middle and high school science teachers and their students, athletic staff checking outdoor conditions, and anyone learning how the forecast’s feels-like number is made.
Format
Browser calculator for a phone, tablet or computer, by touch or keyboard. Fahrenheit and mph or Celsius and km/h. Up to 60 readings. Prints a log; downloads a spreadsheet (.csv); export and import a file.
Access
Free. No account, no sign-in and nothing to install. Everything you type stays in this browser; nothing is sent to Caveat.
Where it lives
The For Teachers space in Caveat Teaching.
Support
Questions, a correction or a request: team@caveatacademic.com.

How to use it

  1. Choose Fahrenheit and mph or Celsius and km/h.
  2. Add a line for each reading: when or where, air temperature, wind speed and humidity.
  3. Read what each reading feels like and which formula applied.
  4. Graph the downloaded spreadsheet, or compare readings across days and places.
  5. Print the log for a lab notebook.

Log a reading

How feels-like is worked out

Two formulas, each with the conditions where it applies.

Wind chill (NWS, 2001)When air ≤ 50°F and wind ≥ 3 mph:35.74 + 0.6215T − 35.75V^0.16 + 0.4275T·V^0.16T = 18°F, V = 15 mph3.7°Ffeels like, Jan 12 at the bus stopHeat index (NWS)When the result is 80°F or more:Rothfusz regression in T and RH,with two small correctionsT = 92°F, RH = 70%112.2°Ffeels like, Jun 3 on the trackWind chill (NWS, 2001)When air ≤ 50°F and wind ≥ 3 mph:35.74 + 0.6215T − 35.75V^0.16 + 0.4275T·V^0.16T = 18°F, V = 15 mph3.7°FJan 12, bus stopHeat index (NWS)When the result is 80°F or more:Rothfusz regression in T and RH,with two small correctionsT = 92°F, RH = 70%112.2°FJun 3, track
The two National Weather Service formulas with readings from the worked example: 18°F with a 15 mph wind feels like 4°F; 92°F at 70% humidity feels like 112°F.

Wind chill

Wind carries heat away from skin, so cold air feels colder in a wind. The 2001 wind chill formula, adopted in the United States and Canada, models heat loss from the face of a person walking at about 3 mph into the wind. It is defined only for air at 50°F (10°C) or colder and wind of at least 3 mph; outside that range the page reports the air temperature.

Heat index

Humid air slows the evaporation of sweat, so hot air feels hotter. The National Weather Service first applies a simple formula; when the result averaged with the air temperature is 80°F or more, it uses the Rothfusz regression, then subtracts a little for very dry air between 80 and 112°F and adds a little for very humid air between 80 and 87°F. The values assume shade and a light wind; full sun can add up to 15°F.

Sources

  1. National Weather Service. Wind Chill Chart and the 2001 Wind Chill Temperature index (weather.gov/safety/cold-wind-chill-chart): the formula and its limits.
  2. National Weather Service, Weather Prediction Center. The Heat Index Equation (wpc.ncep.noaa.gov/html/heatindex_equation.shtml): the simple formula, the Rothfusz regression and the two adjustments.
  3. Rothfusz, L. P. (1990). The Heat Index “Equation”. NWS Southern Region Technical Attachment SR 90-23.
  4. National Weather Service. Heat Index safety page (weather.gov/safety/heat-index): the Caution, Extreme Caution, Danger and Extreme Danger categories and the note that full sun can add up to 15°F.

The worked example is made up. Feels-like values are estimates for shade and a light wind; follow your school’s and your local weather service’s heat and cold guidance for outdoor activity. Your readings stay in this browser. Support: team@caveatacademic.com.