Weather data, methods and evidence

Forecasts and weather-based guidance have different meanings. The following documents the app’s data inputs and the evidence used by its lifestyle modules.

Forecasts, hourly conditions, station temperature and active alerts: US National Weather Service / NOAA, https://api.weather.gov/ . Alert availability is distinct from an empty alert list.

Location search: OpenStreetMap Nominatim, https://nominatim.openstreetmap.org/ . Search is US-only and throttled.

UV and pressure enrichment: OpenWeather through WeatherVibe's server adapter. UV reports explicit availability.

Pollen: Google Pollen API, Universal Pollen Index (0–5), with geographic and seasonal availability.

Air quality: Google Air Quality primary, AirNow and OpenWeather fallbacks. US EPA AQI; modeled fallbacks are marked estimated. Fetched when the air card is enabled.

Aurora: NOAA SWPC OVATION and Kp, with VIIRS light-pollution context. Fetched when the aurora card is enabled.

Sun and moon: local astronomical calculations. Event times are serialized as ISO timestamps; browser-local day boundaries apply. Meteor and eclipse information comes from finite bundled catalogs, not a live discovery feed.

Dark-sky destinations: Spinner et al. (2024), Administrative boundaries of selected certified International Dark Sky Places, GFZ Data Services, https://doi.org/10.5880/GFZ.1.4.2024.005 . CC BY 4.0; processed into a bundled destination list.

Radar: interactive map imagery in the app, not a numeric radar-analysis tool.

Provider refresh times and caches differ. Retrieval time is not necessarily observation time. Missing feeds are not zero-risk readings.

Health-related cards (Skin, Migraine, Aches, Pollen, Air Quality, Hydration, Mosquito, Tick) are general information, not medical advice. For anything you manage clinically, follow your doctor or care team.

Frizz Forecast

Evidence: established

Human hair is hygroscopic, meaning it absorbs moisture from the air. When the Dewpoint rises above 60°F (15°C), the increased atmospheric moisture breaks the hydrogen bonds in hair proteins (keratin), causing them to swell and reshape irregularly—resulting in frizz. We monitor dewpoint specifically, as it is a more accurate predictor of frizz potential than relative humidity alone.

Run Report

Evidence: established

Running comfort tracks how it feels, not the raw thermometer. We use Apparent Temperature (Steadman/BoM — humidity and wind folded in) for the heat and cold tiers, so wind chill escalates cold and humidity flags muggy heat. On clear days a weighted score of feels-like comfort and wind grades the run; storms, ice, and frostbite-level cold override with their own specific warnings.

Skin Health

Evidence: established

Two independent things drive skin. Oil and sweat rise with skin temperature — sebaceous output increases as you warm up. Water loss (trans-epidermal water loss) is driven by the air itself. We split them the way clinicians do: Dry skin lacks oil — typical of cold, low-dewpoint air (which is parched once it's heated indoors) and best met with lipid-rich emollients. Dehydrated skin lacks water — caused by a high Vapour Pressure Deficit, where hot, dry air pulls moisture out fast; it can occur even on oily skin and calls for water-binding humectants rather than heavy oils. Hot, dry conditions push both at once, which is why they read as Dehydrated rather than simply Oily or Dry.

Migraine Meter

Evidence: mixed

Many migraine sufferers are barometric-sensitive. Rapid drops in Barometric Pressure (typical of approaching storms) create a pressure differential between the atmosphere and the sinus cavities/inner ear, which can trigger pain. We compute the 3-hour pressure trend from nearby weather-station observations and flag a fast drop, plus storm fronts and extreme heat. The barometric–migraine link is real but varies a lot between individuals — treat this as a heads-up, not a diagnosis.

Aches & Pains

Evidence: mixed

Joint pain is often linked to Barometric Pressure changes. As external air pressure drops before a storm, tissues around the joint can expand slightly, increasing sensitivity in nerve endings for those with arthritis or old injuries. Cold, damp air further thickens synovial fluid, reducing lubrication and adding stiffness. We flag a falling 3-hour pressure trend and cold-damp conditions. Evidence here is mixed — reported by many, not universal.

Sun Protection

Evidence: established

Ultraviolet (UV) radiation consists of UVA (aging) and UVB (burning) rays. With a live UV Index we follow the WHO bands to recommend a minimum SPF — from SPF 15 at low UV to SPF 50+ at very-high/extreme — and even on cloudy days up to 80% of UV penetrates, spiking near reflective surfaces (water/snow). We also estimate burn time: the Minimal Erythemal Dose (MED) is the UV dose that reddens skin, so dividing your skin's MED by the current erythemal intensity gives how long bare, unprotected skin takes to start burning. Because MED rises steeply with melanin, we personalize it to your skin tone (set it in Settings) — very fair skin can burn in under 15 minutes at high UV, deeper tones take far longer, though everyone can still burn. That burn time is when to start protecting, not a safe limit: SPF, shade, hats, and reapplying all extend it.

Golden Hour

Evidence: established

Golden Hour: occurs twice daily — after sunrise and before sunset — when the sun is between roughly 6° above and 4° below the horizon; sunlight travels through more atmosphere, scattering blue light and leaving the soft, warm reds and oranges photographers prize. Viewing conditions: we rate the sunrise/sunset from cloud cover — high/mid clouds catch color ('Dramatic'), clear skies give a clean gradient, rain washes it out. Astronomical precision: the sunrise, sunset, and golden-hour windows are computed locally from your latitude/longitude and the Julian date.

Pollen Count

Evidence: established

This card reads the Google Universal Pollen Index (0–5), a model that blends species-level plant data with weather to estimate airborne grass, tree, and weed pollen. Pollen release is temperature- and wind-driven — dry, breezy days loft and spread grains, while rain washes them out — and tends to peak mid-morning. We surface the dominant source and an index level so allergy-prone users can plan outdoor activity around the day's forecast. If your doctor or care team already has you on antihistamines, they generally work best taken before exposure rather than after symptoms start — check the timing with them. This is general information, not medical advice.

Air Quality

Evidence: established

This reads the live US EPA Air Quality Index (AQI) for your area — a 0–500 scale that rolls up pollutants like fine particulate (PM2.5) and ozone into one number, and we surface the dominant pollutant driving it. The bands and exertion guidance are the EPA's own public-health language: below 50 is clean, 51–100 is moderate, and 101+ is where sensitive groups (asthma, heart or lung conditions, kids, older adults) should start easing off prolonged outdoor exertion. Air quality swings with wind, wildfire smoke, and temperature inversions. The reading is high-resolution — accurate to roughly your neighborhood.

Aurora Viewing

Evidence: established

Aurora is driven by geomagnetic activity — charged particles from the sun exciting the upper atmosphere. We read NOAA SWPC's OVATION model, which forecasts the probability of visible aurora on a global grid, so it already folds in space weather and your latitude. Then we knock that probability down for everything that actually stops you seeing it: daylight (we require real darkness — the sun well below the horizon), cloud cover, moonlight (a bright moon washes out faint aurora), and light pollution — measured at your exact location from NASA's VIIRS satellite night-lights. The darker your sky, the better your odds; when city glow is the limiting factor, we point you to the nearest certified Dark Sky Place. We also read NOAA's 3-day storm forecast (the Kp index), so when it's quiet here tonight we can flag the next night a storm could bring the lights your way — and whether it'll reach your latitude or you'd need to drive north.

Moon Phase

Evidence: established

A moon phase is the fraction of the Moon's disk lit by the sun as seen from Earth, cycling every ~29.5 days from new → full → new. We work it out from the sun and moon positions for today — the illuminated percentage and your moonrise / moonset times. We also flag the special ones from the Moon's distance and timing: a Supermoon (full moon near its closest approach — bigger and ~30% brighter), a Micromoon (near its farthest), and a Blue Moon (the second full moon in a calendar month). Beyond being nice to track, the phase drives night-sky darkness: a bright gibbous or full moon washes out faint stars, the Milky Way, and aurora, while the nights around a new moon give the darkest skies for stargazing.

Meteor Showers

Evidence: established

Meteor showers happen when Earth plows through the debris trail of a comet (or asteroid); the dust burns up as 'shooting stars' that appear to radiate from one point in the sky. They recur on roughly the same dates each year — the major ones (Quadrantids, Lyrids, Perseids, Geminids, and more) each with a typical peak rate (meteors per hour under dark skies). What really decides whether you see them is the Moon: we compute its phase at the shower's peak, because a bright moon drowns out all but the brightest meteors, while a peak near new moon is prime. Using your location we also point you toward the radiant — the spot the meteors stream from — and the hour it rides highest; face roughly that way, but let your gaze drift across the whole sky, where the longest trails appear. Get away from light pollution — the card points you to the nearest Dark Sky Place — lie back, and give your eyes 20 minutes to adjust.

Eclipse Watch

Evidence: established

An eclipse is a precise alignment of the Sun, Earth, and Moon. In a solar eclipse the Moon passes in front of the Sun; in a lunar eclipse the Earth's shadow falls on the Moon — and a total lunar eclipse turns it deep red, a Blood Moon, as sunlight bends through Earth's atmosphere. These are predicted years ahead with great precision, so we count down to the next one visible from the US. Solar eclipses are only seen along a narrow path; lunar eclipses are visible from the whole night side of Earth, so they're the ones most people catch. (Never look at a solar eclipse without proper eye protection.)

Yard Work

Evidence: established

Comfortable, safe outdoor work depends on more than the thermometer. We score each upcoming daylight hour on apparent temperature (humidity and wind chill folded in), wind, and the chance of rain, then surface the best stretch of the day. Hot, muggy afternoons and gusty or wet hours score low; mild, calm, dry hours score high — so you can time mowing, planting, or raking for when it's actually pleasant. On hot days, favor the cooler morning window and take water and shade breaks.

Firepit Night

Evidence: established

A good backyard fire is mostly about wind and dryness. We scan the evening's hours for a calm, rain-free stretch — strong wind scatters embers and smoke and is a genuine safety hazard, while damp conditions make for a smoky struggle. Cool, still, clear nights score best, and we point you to the calmest, driest window after dark. Always check local burn bans and fire-danger ratings first, and keep water or a hose nearby.

Car Wash

Evidence: established

There's little point washing the car if rain is on the way. We look at the probability of precipitation across roughly the next day or two and translate it into a simple call — wash today, or wait. Low odds mean it should stay clean; rising odds mean you might be wiping it down again soon. When rain is coming, we flag about when it's likely to start.

Hydration

Evidence: established

Your body loses water faster in heat, dry air, and strong sun, through sweat and breathing. Starting from a typical daily baseline, we nudge a rough target upward as the day's high temperature, low humidity, and UV climb. It's a general nudge to drink before you feel thirsty — not a medical prescription. People sweat at very different rates, so adjust for your own activity and body, drink to thirst, and follow your doctor or care team for any condition that affects how much fluid you should take in.

Best Day Out

Evidence: established

Picking a day for a hike, a cookout, or a ballgame is really a comparison problem. We score each upcoming daytime in the 7-day forecast on the things that make being outside pleasant — a comfortable temperature (sweet spot around 72°F), low chance of rain, gentle wind, and no thunderstorms — and surface the day that comes out on top. It's a quick way to aim your weekend plans at the nicest weather instead of guessing.

Best Day In

Evidence: established

The flip side of picking the best day to be outside: the day weather least favors it is the natural one to spend indoors — a movie, a museum, errands, or a cozy day at home. We run the same comparison across the 7-day forecast and flag the wettest, coldest, or windiest daytime, so you can line up your indoor plans with the day you'd least want to be out anyway.

Mosquito Index

Evidence: established

Mosquitoes are cold-blooded, so their activity tracks the weather. They're most active in warm air (roughly 70–90°F) and humid conditions — they dry out fast in low humidity — and a breeze above ~10 mph largely grounds them. Standing water from recent rain gives them places to breed, and biting peaks around dawn and dusk. We blend today's temperature, humidity, and wind with the time of year (peak mid-summer) into a simple activity read. It's a general guide to how bothered you'll be, not a local count — actual numbers depend on your immediate surroundings (still water, shade, vegetation).

Tick Index

Evidence: established

Ticks 'quest' for hosts from grass and leaf litter, and they dry out easily — so their activity rises in mild temperatures (active from the low 40s°F up) and humid, moist conditions, and falls in heat waves and hard cold. In much of the US activity has a spring peak (when tiny, easy-to-miss nymphs are out — the riskiest stage for disease) and a second peak in fall. We combine today's temperature and humidity with that seasonal pattern into a general activity read. It's not a local count; if you've been in grass or woods, do a tick check regardless — and remove any attached tick promptly. General information, not medical advice.

Sideline Style

Evidence: established

Watching a game or an outdoor show is different from being active in the same weather. Moving around, your muscles generate a lot of heat; sitting still you produce far less, so the same temperature feels noticeably colder — which is why bleachers get chilly fast. We take the 'feels like' temperature (wind chill and humidity folded in), subtract a sitting-still allowance, and translate it to what to wear. Events also run into the cooler evening, so we look a few hours ahead and dress you for the coldest point you'll be out in — not just how it feels now — and flag when to pack an extra layer, a blanket, or rain cover. In strong sun and heat it flips to hat, water, and shade instead.