Skywatch is a forecasting tool for sailors who want to read the weather themselves. It teaches you the signs as you log them, and gets sharper with use.
First — where are you mostly going to use this?
You can change everything later in Settings.
Tap a sign to log it. Signs not relevant to the season or time of day are hidden.
Weather signs read differently around the world. A veering afternoon breeze is a front in the North Sea but the normal settled sea-breeze in the Mediterranean summer. Tell Skywatch which climate regime you're in and it adjusts its interpretation. Save the areas you sail and switch between them as you move.
Regime sets the engine's prior. Your own local notes — how a named local wind behaves in your bay, a strait that funnels, a downslope draught off the hills — are surfaced on the forecast as a standing reminder. The app can't predict purely local effects; it can make sure your hard-won knowledge is in front of you when you read the forecast.
Skywatch does not send reminders. The accuracy of its forecast depends entirely on how often you log. Set a phone alarm at your chosen interval — most ship's watches sit on the hour or every four hours.
Active passage in changing conditions — log every hour, the same rhythm as a watch officer filling in the log. Catches frontal passages within minutes of them happening.
Standard at sea — log every 4 hours at watch changes, plus dawn and dusk. The shipboard norm. Catches all significant events.
Training ashore — dawn, noon, dusk. Builds the habit on land.
Background — dawn and dusk only. Minimum useful — forecasts will show trends but not specific events.
Whichever rhythm you choose, dawn and dusk observations carry signs that don't appear at other times — red sky, dew, swallow height, horizon clarity at low sun.
Phone barometers drift over time. Calibrate against a known reading (a real aneroid, or the nearest met station) every few weeks.
Tick the categories and individual signs you want to track. Signs marked ★ are the essentials — best documented, easiest to observe, highest confidence.
Quick-switch your sign library to a different preset.
All observations are stored only on this device. Nothing is sent anywhere. Clearing your browser data will erase the logbook.
Skywatch is a forecasting tool that uses the signs sailors have read for thousands of years — clouds, pressure, wind shifts, bird behaviour, the look of the horizon — and combines them into a 24-hour outlook.
It runs entirely on your device. No internet, no server, no account. The forecast is generated from the signs you log, weighted by their textbook reliability and how recently you observed them.
Each sign you log contributes points to one or more outlook bands: settled, deteriorating, front passing, unsettled, gale risk, thunder risk. Recent observations weigh more heavily than older ones. The engine also watches for recognised sequences — cirrus thickening to altostratus over six hours is read as an approaching warm front, even if neither sign on its own would be decisive.
The pressure tendency is calculated from your pressure log. A fall of more than 2 hPa over three hours adds weight to the gale risk band. A steady rise after a low adds weight to the post-frontal pattern.
The forecast panel shows which signs contributed and how strongly. This is deliberate — the point is to teach you the reasoning, not hide it.
When the app makes a prediction, it asks you to verify it 12 and 24 hours later. Just a quick tap — what actually happened? That record is being collected from your very first observation. Today it's a logbook of how often the app was right; the closing of the loop — the engine reading your own hit/miss record and tuning its sign weights to your waters — is the next major piece of work. See the roadmap below.
The textbook this app draws on is largely North-Atlantic and North-Sea lore: travelling depressions, fronts, backing and veering winds, red sky at night. That lore is wrong in places. In a Mediterranean summer the daily sea-breeze cycle — calm at dawn, an onshore wind building and rotating through the afternoon, dying at dusk — is the settled pattern, but the North-Sea reading of that same wind shift is "cold front through". Under Settings → Places you tell Skywatch which climate regime you're in — temperate maritime, temperate inland, inshore waters, Mediterranean, or trade-wind — and set the hemisphere so the seasons read the right way round. The engine then corrects the most divergent rules. You also record your own local notes — how a named local wind behaves in your particular bay, a strait that funnels — and those appear on the forecast as a standing reminder. The app cannot predict purely local effects; it can keep your own knowledge in front of you at the moment you need it.
Skywatch is built in the open and improves in deliberate steps. What's planned, roughly in order:
Reading the weather from natural signs is a learned skill, not a magic trick. The first few weeks of using Skywatch you should treat the forecasts as indicative — the engine has the textbook rules but no idea yet which signs work where you sail. Trust your own observation, learn from when the app gets it wrong, and over months the two will start to converge.
This app exists because the body of knowledge it draws on is, in the strict practical sense, a backup. If GPS goes down, if the VHF radio fails, if the published forecast is wrong about your specific stretch of coast — you still have eyes and a barometer. Those have brought sailors home for centuries. Skywatch is a tool for keeping that skill alive.
Reading sources: Simon Rowell, Weather at Sea. Tristan Gooley, The Secret World of Weather and How to Read Water. Jim Woodmencey, Reading Weather.