Conditions tools adjust a cool-weather goal pace for temperature, humidity, wind, and elevation using published slowdown heuristics. Heat and humidity can be combined. Headwind and tailwind are opposite signs of the same wind factor.
Altitude pages either slow a sea-level goal for elevation or invert an altitude race pace toward a sea-level equivalent. The conditions board stacks every factor on one screen.
The race weather calculator is the first external API in the lab: Open-Meteo supplies temperature, humidity, wind, and precip; the pace model stays deterministic and local. Manual entry always works if the forecast fails. These are planning estimates, not race-day guarantees.