By now you know the pieces. A prediction market lets people buy shares that pay $1 if something happens (Chapter 2). Weather is forecastable but never certain (Chapter 3). A well-calibrated probability plus a price gap gives us an edge (Chapter 4). And the crowd systematically overpays when the outcome feels uncertain (Chapter 5). This chapter connects those pieces into a single, honest pipeline — the exact chain of steps that turns a weather forecast into a decision to buy, skip, or pass.
Think of it as a factory line. Raw material goes in one end — the atmosphere, and a market quoting a price. A finished decision comes out the other — buy this many shares, or nothing at all. In between are five stations, and a share only becomes a bet if it survives every one of them. Let's walk the line.
Start with a probability, not a guess
The first station produces a number: the chance that some specific weather event happens. Not "it'll probably be hot" — an actual percentage, like "there is a 71% chance the high in Chicago tomorrow is above 90°F."
Where does that number come from? We don't run one forecast; we run a crowd of them. An ensemble is a large batch of forecasts, each started from a slightly different guess about the current state of the atmosphere, because we never measure the present perfectly. polyAether blends roughly a 122-member ensemble drawn from three of the world's major weather models — the American GFS, the German ICON, and the European ECMWF. (A "model" here is just a giant physics simulation of the atmosphere; each institution runs its own.)
Why a crowd? Because the spread of the ensemble is itself the forecast of uncertainty. If 87 of 122 members land above 90°F, that's a 71% probability — and the fact that 35 disagreed tells us how firm the call is. One forecast gives you a guess. A hundred forecasts give you a probability and an honest measure of your own confidence.
A single forecast is a guess. A large ensemble — many forecasts from many models — turns that guess into a probability, and the disagreement among members is a built-in confidence meter.
Pin the forecast to the exact station
Here's a subtlety that quietly sinks amateurs. A weather model doesn't report the temperature at the exact rooftop thermometer the market cares about. It reports the temperature for a grid box — a chunk of sky maybe several miles across, averaged and smoothed. But the market settles on one specific, official instrument: a particular airport weather station.
The model's grid box and that one thermometer are not the same thing. The station might sit in a valley that runs a couple of degrees cooler, or on a sun-baked tarmac that runs warmer. If you bet the raw model number, you're betting on the wrong place.
Calibration fixes this. We take the model's history and the station's history and learn the persistent offset between them: "at this station, the model tends to read 1.4°F too warm, and it's a little overconfident near the threshold." Then we correct the live forecast the same way. polyAether does this for roughly 80 curated stations — a deliberately small, well-understood set, not the whole map — because a probability you can trust at one station beats a vague one everywhere.
Markets settle on one exact thermometer, not a smeared model grid box. Calibration learns the persistent difference between the two so our probability describes the place the bet actually pays on.
Our probability versus the market price
Now we have a trustworthy number — say 71%. The market is quoting a price for the same event. Remember from Chapter 2 that in a prediction market the price is a probability: a share that pays $1 if the event happens, trading at 58¢, means the crowd is pricing the event at 58%.
So we lay the two side by side. We think 71%. The crowd says 58%. That gap — 13 percentage points — is our edge: the amount by which we believe the market is mispriced. If our number and the market's number match, there's no edge and no reason to trade. The whole business lives in the gap.
An edge is not free money
A 13-point gap looks like an easy win. It isn't — not yet. Every real trade drags along costs that eat into that gap, and a bet only makes sense if the edge is bigger than all of them combined.
What eats the edge?
- The spread. The best price to buy at and the best price to sell at are never the same; the difference is the bid-ask spread, a toll you pay just to get in and out.
- Fees. The venue takes a cut of trades or winnings.
- Slippage. If you buy more than a few shares, you push the price against yourself — the cheap shares run out and you pay more for the rest.
- Our own uncertainty. We're 71% confident, but we're not certain we're right about being 71% confident. We shave the edge to stay honest.
So the rule is blunt: trade only where the edge clears every cost with room to spare. A 13-point gap against 4 points of total costs is a real 9-point edge — worth it. A 3-point gap against those same costs is a loss dressed up as an opportunity — skip it. Most candidate markets die right here, and that's the pipeline working, not failing.
The edge is the gap minus the spread, fees, slippage, and a safety margin for our own error. We only bet when what's left is clearly positive. Passing on thin edges is a feature.
Decide how much to risk
The final station answers a different question. The first four decided whether to bet. The last decides how big. This matters enormously: a genuine edge can still ruin you if you bet too much on any one thing and a run of bad luck wipes out your bankroll before the math has time to work.
The size scales with the edge and with our confidence — bigger, surer gaps get more money; thin, shaky ones get a token stake or nothing. polyAether does this with a shrunk-down version of a classic betting formula (the Kelly criterion, which Chapter 8 covers in full), plus hard caps: a limit per market, a limit on total exposure, a daily loss limit, a cap on making too many bets that would all win or lose together, and a kill switch that halts everything if things go wrong. Sizing is where an edge turns into a survivable strategy — so it gets its own chapter.
Why the whole chain matters
Any single station done well is worthless if another is done badly. A brilliant forecast pointed at the wrong thermometer is wrong. A real edge sized recklessly is a blow-up waiting to happen. A perfectly sized bet on a gap that fees erase is a slow bleed. The value isn't in any one clever step — it's in refusing to skip any of them. Discipline, not genius, is the product.
One honest caveat, repeated because it's true: polyAether is strictly paper-trading right now — every bet in this pipeline is simulated, with no real money and no proven track record. The chain is built and tested; it has not yet earned its keep. Chapter 7 tackles the sneakiest station of all — how a market actually settles, which decides whether your winning bet actually pays.