Hawaiian islands with greener windward slopes, drier leeward slopes and silvery sunglint on the Pacific.

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Preparing the 3D view

Preparing lighting and the first complete frame…

Model scale

Relief ×2.5. parcel ascent and descent. simplified lapse rates.

Parcel 1490 m · 8.4 °C · RH 100%. Cloud base ≈ 705 m.

How to read these results

Start: 20 °C, 70% RH. Leeward sea-level air: 25.3 °C, 34% RH. Condensation removes moisture as the air crosses the ridge.

Rain shadow

Explain why rising air cools and produces rain on a windward slope, leaving drier conditions on the leeward side.

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Why it happens

Rising air expands and cools. If it reaches saturation, condensation can occur; after moisture is lost, descent on the far side of a ridge can bring warmer, drier air to the same elevation.

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Terra MODIS, 27 May 2003. Northeasterly trade winds favour wetter, greener windward slopes; leeward slopes are drier. The bright ocean is sunglint.

Try a comparison

Compare 70% and 2100 m; follow the parcel through cloud base. Read temperatures at both feet and explain the difference.

Reading the result

The parcel uses simplified lapse rates and assumed condensate loss; it calculates a temperature comparison rather than rainfall amounts.

A common misunderstanding

A mountain creates the moisture that falls as rain on its windward side.

The approaching air already contains water vapour. Forced uplift makes the air expand and cool; if saturation is reached, condensation and precipitation may follow. After moisture loss, descending air can become warmer and drier on the leeward side, although the outcome depends on the incoming conditions.

Cases

Process0.40Ridge height2100 mInitial humidity70%