About & Methodology

Key Points

  • Practice-Day Alerts provides real-time heat index, wind-chill, air-quality, and weather-hazard (thunderstorms and rain) status for organizations and schools.
  • Thresholds align with national risk guidance from NWS (heat, wind-chill, lightning), NATA/NFHS sports-medicine recommendations, and EPA/AirNow (air quality).
  • Weather and precipitation data come from the Open-Meteo Forecast API; air quality uses WAQI when available, with the Open-Meteo US AQI feed as a backup.
  • All of this is translated into simple “OK / Modify / Cancel” categories for each practice area.
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Our Services
Practice-Day Alerts helps organizations decide whether to continue, modify, or cancel outdoor practices based on real-time heat, cold/wind-chill, and air quality conditions near their location. We provide the status on the homepage and optionally provide email reminders.
Data sources
Practice-Day Alerts relies on two primary data feeds:
  • Weather & environmental data – Temperature, relative humidity, wind speed, precipitation, and weather codes (used for thunderstorm detection) are pulled from the Open-Meteo Forecast API for each practice area and refreshed throughout the day.
  • Air quality data – When available, air-quality information comes from the World Air Quality Index (WAQI) API, which reports U.S. AQI for our locations. If the WAQI feed is unavailable or does not return a value, we automatically fall back to the Open-Meteo Air-Quality API, which provides US AQI based on U.S. EPA AirNow formulas. In both cases, the values displayed correspond to the standard U.S. Air Quality Index categories (Good, Moderate, Unhealthy for Sensitive Groups, etc.).
Indices we calculate
To estimate heat stress, we calculate the Heat Index (HI), which combines air temperature and relative humidity to represent how hot it “feels” to the human body. HI is computed using the National Weather Service (NWS) Rothfusz regression and associated adjustments for very dry or very humid conditions. We then interpret those values using conservative thresholds based on NWS Heat Index guidance.
For cold-stress conditions, we compute Wind-Chill Temperature (WCT). This metric is only valid when the air temperature is 50°F or below and wind speed is 3 mph or higher. The calculation follows the official NWS wind-chill formula:
WCT(°F) = 35.74 + 0.6215 T − 35.75 V^0.16 + 0.4275 T V^0.16
where T is air temperature in °F and V is wind speed in mph.
Air-quality status is based on the U.S. EPA / AirNow Air Quality Index (AQI), which classifies conditions as:
  • Good (0–50)
  • Moderate (51–100)
  • Unhealthy for Sensitive Groups (101–150)
  • Unhealthy (151–200), with additional categories for more severe pollution levels.
Finally, we interpret weather hazards (Wx) using the WMO weather code and hourly precipitation rate from Open-Meteo. We detect active thunderstorms and estimate rain intensity (inches per hour) to decide when steady or heavy rain alone should trigger modifications or cancellations.
How we translate conditions into “OK,” “Modify,” or “Cancel”
Each hazard—heat, cold, air quality, and weather hazards (thunderstorms / rain)—is assigned an operational category using conservative thresholds informed by national guidance and common school-sports practice.
Heat (Heat Index)
  • OK – HI < 90°F
  • Modify – HI 90–102°F
  • Cancel – HI ≥ 103°F
These cutoffs are adapted from NWS Heat Index guidance, where “Extreme Caution” begins near 90°F and “Danger” begins near 105°F. We round slightly and collapse the full table into a simple, easy-to-apply three-step system for practices.
Cold (Wind-Chill Temperature)
  • OK – WCT > 15°F
  • Modify – WCT 15°F down to 0°F
  • Cancel – WCT ≤ 0°F
These thresholds follow NWS wind-chill validity rules (only using the formula at or below 50°F with wind ≥ 3 mph) and mirror school-sports recommendations derived from NATA cold-injury guidance, where activity is modified as frostbite risk increases and cancelled at very low wind-chill values.
Air Quality (U.S. AQI)
  • OK – AQI 0–100 (Good / Moderate)
  • Modify – AQI 101–150 (Unhealthy for Sensitive Groups)
  • Cancel – AQI ≥ 151 (Unhealthy or worse)
These align directly with EPA / AirNow AQI breakpoints and are commonly referenced in school and athletic-department AQI policies.
Weather hazards (Thunderstorms & Rain)
  • Thunderstorms: Any active thunderstorm (NWS / WMO weather codes 95, 96, or 99) automatically results in Cancel, reflecting NFHS and NATA lightning-safety guidance and the NWS rule of, “When thunder roars, go indoors.”
  • Rain intensity (no thunder):
    • Light rain is allowed, but once sustained rain reaches roughly 0.05–0.19 inches per hour, practices move into Modify due to reduced footing and visibility.
    • At ≥ 0.20 inches per hour, conditions are treated as Cancel, because fields can become unsafe or quickly waterlogged even without lightning.
The system always takes the highest applicable risk level: if any single factor (heat, cold, air quality, or weather hazard) reaches Cancel, the overall status is Cancel; if none are Cancel but at least one is Modify, the overall status is Modify; otherwise it remains OK.
Why these cutoffs are used
Our thresholds are designed to line up with nationally recognized standards so coaches and administrators can immediately connect PPDA’s color/status categories to familiar public-health and sports-medicine advisories:
  • Heat – NWS Heat Index terminology (Caution, Extreme Caution, Danger, Extreme Danger) and NATA exertional heat-illness guidance both emphasize stepped responses as environmental heat stress increases. We simplify those tables into conservative “OK / Modify / Cancel” bands anchored at HI ≈ 90°F and HI ≥ 103°F.
  • Cold – The NWS wind-chill formula is only applied where it is valid (≤ 50°F, wind ≥ 3 mph). Cutoffs near 15°F (Modify) and 0°F (Cancel) mirror thresholds used in many school-sports policies and NATA cold-injury recommendations, where frostbite risk and equipment limitations require shortened or cancelled outdoor activity.
  • Air Quality – Decisions follow the EPA / AirNow AQI structure exactly, treating 101–150 (Unhealthy for Sensitive Groups) as a Modify range and 151+ (Unhealthy and above) as Cancel.
  • Lightning & Rain – For lightning, we apply the NWS, NFHS, and NATA expectation that play is suspended immediately when thunder is heard or lightning is seen, and only resumed after conditions are clearly safe. Thunderstorms therefore always result in Cancel. For non-thunderstorms, we use standard meteorological rainfall-intensity bands and err on the side of caution: persistent moderate or heavier rain is treated as a reason to modify or cancel outdoor practice due to surface safety, visibility, and equipment concerns.
Because these cutoffs are grounded in public guidance rather than arbitrary numbers, coaches and athletic directors can explain and defend PPDA status calls to families, school leadership, and local health partners.
How the map determines your nearest practice area
If you grant permission, we geolocate your browser and calculate the shortest distance to our predefined practice areas using the Haversine formula. We do not save, store, or retain any information about your location. Your display then reflects the conditions at the closest location. This information is advisory only and does not replace district or league policy, on-site observations, or the judgment of athletic trainers and coaches.
Update frequency and caching
Weather and air-quality data are refreshed each time you load or manually update the page, click the “refresh” button, or immediately before any reminders are sent out. To reduce API demand and improve performance, results are cached in your browser for approximately five minutes before new data is fetched.
Limitations
Local micro-climates—such as shaded areas, turf fields, urban heat islands, or saturated playing surfaces—may differ significantly from forecast model values. Wind-chill is not valid when temperatures exceed 50°F or when wind speeds fall below 3 mph; in these cases, the metric is hidden. Air-quality readings may vary in regions with sparse monitoring stations, where modeled AQI may differ from the nearest physical sensor.
Questions or interested in a pilot?
If you would like to partner or test this system, use the Partner Pilot Request form. We can configure custom practice areas, adjust thresholds to match your district’s exact policy, and set up any necessary email or text routing.
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