The sky that never left the temperate: eight countries under one weather
A world in The Long Watch now runs cold at one end and warm at the other, with eight kinds of country between them. For a week the sky above all of it stayed the same: temperate rain over the desert, temperate warmth over the northern pine, in every world we grew. In late July the weather finally learned to read the ground under it.
The gap had a size. A desert wants roughly a quarter of the rainfall a temperate meadow gets, and it was being handed the meadow’s figure, four times over. The cold north was being held at temperate warmth. Every plant rooting there, every animal grazing there, every riverbank wearing down there read that sky and believed it.
The land moved and the sky stayed
In the middle of July the four climates stopped being four separate worlds and became regions inside one. Warmth now slides along one axis of the map, dampness along the other, and the eight countries are the neighbourhoods of that gradient.
The land took to it at once. Every patch of ground already works out what country it is by reading its own warmth and dampness and taking the closest match, so the moment those readings varied across the map, the countries varied with them. Ask a spot what it is and it answers from where it stands.
Weather had no such habit. It settled on one climate at the moment the world was made, wrote that answer down, and handed the same one to every question asked of it afterwards. Rain, wind and warmth have always been things you ask the world about at a particular spot. The spot just had nothing to say.
The same answer, every time
We expected this to be arbitrary. The plan we wrote for the repair described weather grabbing one of the four temperaments and imposing it on the whole map, a boreal world’s blizzards falling on its own desert. Then we read the live code before writing a line of the fix, and turned up something duller. The list of climates weather chose from had been trimmed during the merge until only its temperate entries were left. There was no roll of the dice in it at all.
So the answer was temperate. For every seed, at every world size, on every run since the merge landed. Which is precisely why nothing caught it: the checks that watch this world are built to prove it rebuilds identically each time, and a wrong answer that never varies rebuilds identically with perfect discipline. We have since gone after that gap by damaging our own code on purpose to see which checks notice.
A wrong answer that never changes looks exactly like a right one holding steady.
There is a second reason it went unseen. The world we watch most closely, the one nearly every long-running check has ever run in, is temperate. Temperate weather over a temperate world is correct. The sky was only wrong in the places nobody had been standing.
Weather that asks the ground
The repair is short to describe, and it landed in a single day across four steps. The system that decides what country a spot is now answers two plainer questions about it as well: how warm is it here, and how damp. Those are the same two readings the country itself is chosen from. Every weather value a place has, its warmth, its rainfall, its wind, is mixed from the four authored climates by how near that place sits to each of them, the nearest counting for most. Stand exactly on one of the four and you get that one, unblended.
Nothing new had to be balanced, which is the part we are most pleased about. The four climates already had temperaments we spent a long while tuning by eye: arid’s hard short downpours, tropical’s wide soaking ones, boreal’s long slow build. Thirty-six numbers, already right. They survive untouched as the anchors the blend hangs on.
And because a blend is a weighted average of those anchors, it can never wander outside them. No combination of warmth and damp anywhere on the map can produce a rainfall drier than the driest we wrote, or a wind stronger than the strongest. The space between the four climates gets filled in. The edges of it stay ours.
Storms take the character of where they form
Storms got the same treatment, one step further in. A storm here has a centre, a width, a strength and a length, and each of those is now read at the point where the storm actually forms. So a storm sitting over dry country behaves like dry country’s weather: sharp, narrow, over quickly. The same storm forming a walk to the south, on the wet flank, spreads wide and settles in.
How often storms happen stayed one figure for the whole world: one and a half a month, the temperate rate, kept on purpose. A world lays out its whole calendar of storms in advance and only then decides where each one lands, so at the moment frequency is settled there is no spot to ask. Making it vary by region means changing how a world is generated, and that can wait.
What a changed rainfall moves underneath
Rain in this world is a force rather than scenery; it is the thing that wears the land down. So the moment rainfall stopped being the same everywhere, the ground began carving itself at different rates in different country, and every measurement we keep on erosion had to be taken again. They were, once it had all settled.
The one thing it did not move was the soil, and only because of a dial we have left at zero. Rainfall can feed the dampness of the ground itself, but that link is switched off today, so plants and soil went on exactly as before. Turn it up and a desert’s dryness stops being a matter of what falls on it and starts reaching the roots. That is a far larger change than this one, and it is waiting.
What ships today is a sentence we can finally write down and mean: a region’s weather agrees with the country it falls on, because both are read from the same ground. The desert is arid overhead as well as underfoot.
