Storm Window Threshold Sources

References for the activity-aware safety thresholds used by Storm Window.

Storm Window combines published weather, sports-medicine, marine, and public-health guidance with activity-specific exposure rules. These references help ground the app’s default thresholds, but Storm Window remains forecast guidance only and is not a safety device.

Heat and heat stress

Storm Window’s Custom Activity profiles (Pro) expose two separate heat tolerances on purpose, and their defaults are set on different scales: Air Temperature Tolerance tracks the NWS Heat Index chart below (temperature adjusted for humidity and wind — the same idea most weather apps call “feels like”), while Heat Stress Index Tolerance tracks Wet Bulb Globe Temperature (WBGT), which adds direct solar radiation on top of that and weighs humidity’s cooling effect more heavily. WBGT reads numerically lower than Heat Index for the same real-world risk — see the Korey Stringer Institute reference below, and the Support FAQ for a fuller explanation with worked examples.

Published Heat Index and WBGT guidance provide the hazard anchors. The practical danger is impaired cooling: dehydration, heat cramps, heat exhaustion, and eventually heat stroke as intensity, humidity, sun, and duration rise. Storm Window’s activity, duration, heat-tolerance, and fitness adjustments are calibration choices that move those anchors earlier or later for the selected profile without changing the reported weather values.

Lightning

Lightning thresholds are anchored to published outdoor-safety guidance: treat thunder or nearby lightning as a stop condition and wait for a clear period before resuming. The danger is direct or nearby strike injury, especially in open fields, on ridges, on water, or near isolated tall objects. Storm Window’s forecast-lightning categories and live-strike handling map provider data into those safety rules; the app may be more conservative for exposed or water-adjacent activities.

Air quality

Storm Window uses the U.S. AQI scale as the public-health anchor. The danger is respiratory and cardiovascular stress from particulates or ozone, with symptoms such as coughing, chest tightness, shortness of breath, or reduced performance. Activity and personal-profile adjustments are calibration choices: higher exertion, longer duration, asthma/COPD sensitivity, and lower fitness can move caution earlier because breathing rate and exposure time change the practical risk.

Wind

Storm Window uses forecast 10 m wind gusts in mph. Published wind advisories and warning criteria provide the hazard anchors: the baseline thresholds are 25 mph for Use caution, 45 mph for Unsafe, and 58 mph for Dangerous. Around the caution range, gusts can make walking, running, cycling, paddling, or handling a stroller less stable and can turn loose objects, branches, sand, or spray into practical hazards. Near the dangerous range, gusts can break limbs, make control of bikes or small craft difficult, and create conditions consistent with damaging high-wind or severe-thunderstorm criteria. Activity-specific adjustments are Storm Window calibration choices based on exposure, balance/control risk, water safety, and proximity to shelter. For example, Walker starts Use caution at 22 mph; exposed or balance-sensitive activities such as cycling, paddling, sailing, climbing, stroller walks, and snow sports may use even more conservative gust thresholds.

Cold and cold water

Wind chill and cold-water thresholds are anchored to published frostbite, hypothermia, and immersion guidance. The danger is rapid heat loss: exposed skin can freeze in severe wind chill, and cold water can impair breathing, dexterity, swimming ability, and self-rescue before full hypothermia develops. Storm Window’s activity adjustments account for exposure, wetness, expected duration, access to shelter, and whether the selected profile puts the user in or near water; those profile adjustments are app calibration rather than one-size-fits-all public thresholds.

Altitude

Altitude guidance is anchored to travel-medicine references about acclimatization and altitude illness. The danger is reduced oxygen availability: users may fatigue sooner, dehydrate faster, and develop headache, nausea, dizziness, or more serious altitude illness when ascending too quickly. Storm Window treats altitude as an advisory factor for relevant profiles; exact caution bands are calibration choices based on elevation, expected exertion, and the activity’s tolerance for reduced aerobic capacity.

Marine weather

Marine thresholds are anchored to NOAA marine warnings and common small-craft guidance. The danger is loss of control and reduced rescue margin: waves and gusts can capsize small craft, separate swimmers from shore, increase fatigue, and make returning or being recovered harder. Storm Window calibrates wave, wind, water-temperature, and lightning sensitivity by activity because a paddler, swimmer, sailor, and offshore boater have very different exposure and self-rescue margins.