A small change.

Cirrusfold · Clear-Sky Passage is an original browser game about changing an altitude profile around ice-rich air. Shape seven interior waypoints, respect each flight’s climb limit, balance wind and climb fuel, and meet both allowances. Eight handcrafted crossings have exact, independently verified gold targets.

Scientific concept reference: contrailcirrus/pycontrails, Apache-2.0. Observed November 9, 2026: 114 stars, repository pushed November 7, commit f47646144218dfe9e5b32836de9ad853705a5239 committed November 7. PyContrails is a Python aviation-climate modeling library. No upstream code, weather, aircraft data, models or artwork is included in this original JavaScript toy.

Current context: NATS · Operation Blue Skies (August 2026) describes altitude-adjustment trials planned for winter 2026–27 and 2027–28. Google · Asia-Pacific contrail-avoidance trial (September 2026) discusses cold, humid air and predictive route adjustments.

This game uses fictional zones, eight equal legs, seven altitude choices and simplified integer scores. Trail points measure sampled exposure, not actual radiative forcing, emissions or a forecast. Fuel points are illustrative: cruise is easiest near the mint arrows and climbing adds cost. The exact solver keeps nondominated fuel/trail pairs and finds the least fuel under the trail limit. All 171,666 legal authored routes were independently enumerated to verify these frontiers.

Original code: MIT license. Three assets generated for this game with a GPT image model: a coral-tailed jet, translucent cirrus ribbon and painted Atlantic sky. All are optimized local WebP files and drawn in the playable canvas. No external fonts, runtime dependencies, server, database, authentication, popup or download required.

Route plans and best clearances stay in this browser’s local storage. Reset and Undo keep earned logbook entries. Metadata tags: github-source, game.