About
ClearOutside is a specialist weather forecasting platform built specifically with astronomers in mind. Unlike generic weather services, it breaks down cloud cover into low, medium, and high layers, giving observers a precise picture of how the sky will behave at altitude — critical information when planning deep-sky imaging or visual observing sessions. The platform offers 7-day forecasts with hourly resolution, presented through an easy-to-read red/amber/green traffic-light system that rates each hour as Bad, OK, or Good for observing. Beyond clouds, ClearOutside tracks precipitation probability, fog, wind speed, temperature, dew point, humidity, and atmospheric pressure — all the variables that affect a night at the telescope. Astronomy-specific data includes precise civil, nautical, and astronomical darkness times, moon phase and rise/set times, sun transit data, estimated sky quality (Bortle scale and magnitude), and ISS passover visibility windows. An annual darkness chart helps observers plan long-range sessions across an entire year. Available as a free web app and free iOS and Android apps, ClearOutside supports any location worldwide via address, town, postcode, or manual latitude/longitude entry. Forecasts can be embedded and a default location can be saved, making it quick to check conditions every clear night. It is an essential free tool for backyard astronomers, astrophotographers, and observatory operators who need reliable, astronomy-focused sky transparency forecasts.
Key Features
- Layered Cloud Cover Forecasting: Breaks sky cover into low, medium, high, and total cloud percentages hourly so astronomers know exactly which layer might obstruct their view.
- Traffic-Light Observing Ratings: Each hour is rated Bad, OK, or Good using an intuitive red/amber/green system, making it instant to spot the best windows for stargazing.
- Astronomical Darkness & Moon Data: Provides civil, nautical, and astronomical darkness start/end times, moon phase, and moon rise/set times to help plan sessions around natural light.
- ISS Passover & Sky Quality Estimates: Shows ISS visibility windows and estimated sky quality in Bortle scale, magnitude, and millicandellas per square metre for any location.
- Annual Darkness Chart: A full-year darkness overview lets astronomers plan observing campaigns and holidays around optimal dark-sky periods well in advance.
Use Cases
- An amateur astronomer checks the nightly forecast to decide whether to set up their telescope, using the traffic-light rating to identify the best clear hours.
- An astrophotographer plans a multi-night imaging run of a deep-sky nebula by consulting the 7-day hourly cloud forecast to choose the least-interrupted window.
- A star-party organiser uses the annual darkness chart to select future event dates that maximise astronomical darkness for a group of club members.
- A visual observer uses the moon phase and rise/set times alongside the darkness windows to plan sessions that avoid lunar interference on faint objects.
- A backyard observer travelling to a dark-sky site looks up sky quality estimates (Bortle class) and ISS pass times for the destination before departing.
Pros
- Completely Free: The web platform, iOS app, and Android app are all free with no paywalled features, making professional-grade sky forecasting accessible to every astronomer.
- Astronomy-Specific Data: Goes far beyond generic weather apps by including Bortle scale, darkness windows, moon phases, and ISS passes — everything an observer actually needs.
- Worldwide Coverage with Easy Location Input: Supports any global location via address, postcode, or manual coordinates, with the ability to save a default location for quick daily checks.
- Hourly 7-Day Resolution: Hour-by-hour forecasts over seven days let observers plan sessions days in advance and avoid wasted trips under cloudy skies.
Cons
- No AI-Powered Personalization: Forecast display is the same for all users; there is no machine-learning layer to learn observer preferences or telescope equipment constraints.
- Forecast Accuracy Varies by Region: Like all numerical weather prediction services, accuracy degrades at longer lead times and in areas with sparse weather-station coverage.
- Limited Seeing & Transparency Data: Does not natively include atmospheric seeing index or scintillation forecasts, which astrophotographers often also need alongside cloud cover data.
Frequently Asked Questions
Is ClearOutside free to use?
Yes, ClearOutside is completely free. The website, iOS app, and Android app all provide full forecasts at no cost.
How do I look up a forecast for my location?
Enter your address, town, or postcode in the search box on the homepage, or manually enter a latitude and longitude to get a precise local forecast.
What does the traffic-light rating (Bad/OK/Good) mean?
Each hour is assessed against cloud cover, transparency, and other factors. Green/Good means favourable conditions for observing, amber/OK means marginal conditions, and red/Bad means the sky is likely unsuitable.
What is the Bortle scale shown in the forecast?
The Bortle scale (1–9) rates the darkness of a location's night sky. Lower numbers indicate darker skies with less light pollution — more suitable for deep-sky observing.
How far ahead does ClearOutside forecast?
ClearOutside provides a 7-day forecast with hourly resolution, updated regularly throughout the day as new weather model data becomes available.
