Isobar

How to Play Isobar

Isobar puts you at the desk of a small coastal forecasting office. Every morning the wall chart shows lines of equal pressure, the fronts that bring rain and wind, and plotted reports from stations along the coast. Your job is to forecast for the next 24 hours: drag each low, high and front handle to where you expect it to be tomorrow, then set a call for every town on the coast.

Press and drag a round handle on the chart, with a mouse or a finger. Lows and highs have one handle each, and every front has two, one partway along its length and one at its tip. A pencil-grey dashed copy shows where your forecast puts each feature, with a thin line back to where it sits now. Positions snap to half a map cell, or to a quarter cell once the sharp pencil is on your shelf. With the keyboard, click the chart or tab onto it, then use the arrow keys to move the selected handle, Shift for bigger steps and Enter to file. Reset to today puts everything back on its present position, which is a persistence forecast: tomorrow will look like today. It is the baseline to beat.

Below the chart each town has a card with a rain call (none, light or heavy) and a wind call (calm, breezy, strong or gale). The harbour also has a gale warning switch, with the number of fishing boats at stake. Your drawn chart suggests a call for every town, shown as grey dashed chips. A suggestion is not yet a call: tap a chip to make that town's call yours, or press Use chart for calls to accept every suggestion at once, then change any you disagree with. If you file while a town still shows only a suggestion, the game asks whether to use the chart or file that town as no forecast, because a town with weather and no call counts as no forecast. When you are happy, file the forecast. After that nothing can be changed and the overnight replay runs.

Reading the Chart

The brown contour lines are isobars, drawn every four hectopascals with a heavier line and printed value every twenty. Closely packed lines mean a steep pressure gradient and strong wind, and the wind barbs at each station agree: a full barb is ten knots and a half barb is five. A red L is a low, a blue H is a high, and the number beneath is its central pressure. A small arrow beside a low says whether it is deepening or filling, which is your best clue to how stormy it will turn out.

Fronts are the lines with symbols. A cold front is blue with triangles, a warm front is red with half circles, and the symbols sit on the side the front is moving toward. A cold front brings a burst of rain and a gusty wind shift as it passes, and the weather behind a low swings round it in a cyclonic turn. The Steering arrows button, unlocked by the weather balloon from the Instruments shop, shows the flow that carries every feature along, so you can judge how far a low will travel in a day. Systems steered by a stronger current move further, and the flow is not the same in the north as in the south of the chart.

Calls, Scoring and the Fishing Fleet

When the replay ends each town is scored. Rain and wind are worth the most when you name the exact band, and part credit when you are one band out. Wind bands are calm below twelve knots, breezy to twenty-four, strong to thirty-three and gale from thirty-four. Rain is light or heavy depending on how much moisture the model drops on the town during the day. At the harbour the gale warning matters most. If a gale arrives and you warned, the boats stay in port and are saved. If you did not warn, the fleet is caught out and the penalty is heavy. A warning that turns out to be a false alarm costs a smaller penalty because the fleet lost a day's catch.

The chart itself is also scored: the closer your handles are to where the features really ended up, the higher the chart score. Your day score blends the town calls, the chart and the fleet's safety, and it changes your reputation and gold at the office. Every day uses a fixed chart, so day one is the same for everyone and you can compare your forecasts with a friend's.

Seasons, Instruments and the Office

The campaign runs through four seasons: Spring, Summer, Autumn and Winter. Each has twelve forecast days and ends with a named storm finale on a thirteenth day, which counts the fleet for half of the score. That makes 52 scored days. Spring has three towns and asks for rain and wind. Summer has four towns, adds sea fog at Saltmarsh and thunderstorm rain over land. Autumn has four towns with frost at the two farm towns, hill rain and occluded fronts, where a cold front has caught up with the warm one. Winter has five towns, two lows that can merge into one, occluded fronts and frost at the two farm towns. Frost and fog are one extra chip on the town card that you switch on when you expect them.

Each season ends with a grade from S to D, set by the average of its twelve days: S from eighty-five, A from seventy-five, B from sixty-two, C from forty-eight. A finale must score at least forty-eight to open the next season, and a retried finale replaces its earlier score without paying twice. Reputation and gold come from each day's score. Reputation names you Trainee, then Observer from fifteen, Forecaster from forty-five and Chief Forecaster from eighty-five. Gold buys the eight instruments in the Instruments shop, one of each: the weather balloon for the steering arrows, a sharp pencil for finer handles, three sets of outlying stations (two more stations each), ship reports (four weather ships at sea), a brass chronometer that draws your forecast at hour twelve, and coastal radar that shades the moist air on the morning chart. What you own appears on the office shelf above the chart.

Besides the campaign there is a Daily chart, one seeded chart for each UTC date, scored once for the daily board with a ten point bonus for no missed gale, and played on the standard chart without instruments. Once the campaign is finished, Free play offers seeded charts that are never submitted. The game saves after each day and when you buy an instrument, and Continue returns you to the morning chart of the saved day. Sound is made in your browser, starts only after your first tap or key press, and the Sound button mutes it and remembers the choice.

Four more tools sit under the chart. Use chart calls and file confirms every suggestion you have not set yourself and files in one tap, and it keeps any chip you tapped. The sticky File bar at the bottom of a phone screen keeps both file buttons in reach while you draw. Next handle cycles through the lows, highs and fronts, which helps when the handles crowd together on a small screen. List view shows the chart as text, with every system and front, its position and a move button for each direction, so the chart can be played without dragging. Colour-blind mode swaps red and blue for orange and blue, writes the front type on each front, hatches the wet areas and adds ticks and crosses to the results card. On every campaign day you can also stake 20 or 50 gold on your calls once you hold that much gold. Each town whose rain and wind calls were both exact counts as a hit, and the net is the stake times twice the share of hits, minus one: every town right wins the stake, none right loses it, half right breaks even. The day score does not change. The chart is deliberately unsure about the wind at one inland town each day, marked with a question mark. Read the station barbs and the isobar spacing yourself, because the printed call there can be a band out.

Tips and Strategy

• Start with the steering flow. The weather balloon (60 gold, the cheapest instrument) unlocks the steering arrows. Move every low roughly along them before you refine anything; a low usually travels several cells in a day.
• Trust the tendency arrow. A low that is falling in pressure will have a tighter gradient tomorrow, so expect stronger wind at the harbour than the present chart shows. Use Deepen when you expect a storm.
• Cold fronts travel faster than warm fronts. The cold front will catch up with the warm one, so draw its tip further along than you first think.
• Watch the gradient, not the letter. A shallow low with packed isobars near a coast can be windier than a deeper one far out to sea.
• Be wary of false alarms. A gale warning on a day that stays below thirty-four knots costs the fleet a day's catch. Warn when the chart says strong, and when your own drawing agrees.
• Override the chips with reasons. If the drawn chart puts a front a cell short of a town, the town may still get the rain. The chart calls are a starting point, not an answer.

What Makes Isobar Different

Most weather games ask you to guess a single outcome. Isobar asks you to draw the cause. You move the fronts and the lows, the same model that produced the chart then plays out your forecast, and the calls follow from your drawing unless you overrule them. The overnight replay is not a random roll: it runs the same deterministic model forward, so a wrong forecast has a visible reason. That makes it a game of reading patterns and extrapolating them, closer to real forecasting than to a trivia quiz, and every day is a short puzzle with a clear measure of how well you read the sky.

A Brief History of the Weather Chart

Synoptic charts began in the nineteenth century, when the telegraph let observers collect reports from many places at once. After a storm wrecked allied ships in the Black Sea in 1854, the French astronomer Urbain Le Verrier showed that the storm could have been tracked across Europe, which led to some of the first storm warning services. In the years after the First World War, Norwegian meteorologists in Bergen described the polar front, the cold and warm fronts and the life cycle of a cyclone, and the symbols still used on charts today come from that school. In 1950 a team using the ENIAC computer produced the first numerical forecast, and the idea that the atmosphere can be stepped forward by a model is the one behind both modern forecasts and this game.