Raise a ridge in a westerly wind. Rising air cools, clouds form and rain falls on the windward side; the air then descends warm and dry. Height decides the snowline and the treeline, rain decides forest or steppe.
Rebuilds the climate for several ridge heights (other sliders as now) and reports where the snowline and treeline sit and how strong the rain shadow is.
The science
Lapse rates. Rising unsaturated air expands and cools at the dry adiabatic rate Γd = g/cp = 9.8 K/km. Once the parcel reaches saturation (the lifting condensation level, about 125 m × (T − Td) above the start) condensation releases latent heat Lv Δq and the cooling slows to the moist rate, 4 to 6 K/km in mild air. The air temperature that a weather station measures follows the environmental lapse rate, about 6.5 K/km by default (a slider).
Rain shadow. A moist layer 700 m deep moves with the wind and follows the ground. At each 0.94 km step the parcel is lifted or lowered, saturation specific humidity qs(T, p) is found from the Magnus formula, and any excess Δq = (q − qs)/(1 + Lv² qs/(cp Rv T²)) condenses; 60 % of it falls as precipitation at that spot (P = Δq ρ D U / Δx), the rest stays as cloud water that evaporates again on the way down. The water that left on the windward side is gone, so the descending air arrives at the foot of the lee slope warmer and with lower relative humidity (the foehn). Precipitation on flow days is scaled by how often moist flow occurs, and a baseline of frontal rain, wetter in winter, is added everywhere.
Snowline. Monthly temperature is Tsea(month) − Γ h with a sinusoidal year. Snowfall is precipitation weighted by (2 − T)/4 clamped to 0..1 (all snow below −2 °C, all rain above 2 °C); melt follows the positive-degree-day method, 4.5 mm w.e. per °C per day × Σ(days × max(T, 0)). Where yearly snowfall exceeds melt the snow survives: the equilibrium line is where the balance is zero.
Treeline and belts. Trees need a warmest-month mean above 10 °C (the Köppen tundra limit, so the closed form is z = (Twarm,sea − 10)/Γ), alpine meadow lies above that down to 4 °C, below 4 °C is bare tundra or rock. In the warm zone annual rainfall under 450 mm gives dry steppe, a warm month above 17 °C with over 600 mm gives lowland farmland, anything else forest.
What is simplified. One moist layer, constant wind, uniform upwind humidity, no ice-phase physics, no flow blocking, lee waves, thermal circulations or aspect (slope direction) effects, and no glacier flow: perennial snow is shown where the balance is positive, not a real glacier extent. The 10 °C and 4 °C limits, 450/600 mm thresholds, DDF 4.5, 60 % precipitation efficiency, layer depth and the wet-flow frequency are illustrative typical values; results show the mechanism and the sign of effects, not a forecast for a real range.