Bowcast

Rainbow forecast for Fort William

Fort William, Scotland, United Kingdom: today's peak estimated rainbow chance, the best forecast interval to look up, and the week ahead.

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Checking about 40 forecast ensemble members for sunlit rain near Fort William…

Open the live map for Fort William

Rainbow weather in Fort William

Fort William lives under the North Atlantic conveyor: fast-moving showers with bright spells between them, at a latitude where the sun stays low for much of the day. Low sun means tall bows, and "sunshine and showers" is practically the regional forecast. Spring and autumn, when shower trains are busiest, are the best seasons.

At 56.8° north, Fort William's rainbow geometry changes strongly with the seasons. Summer favors early and late hours; the lower winter sun can keep the geometry open longer, although daylight is shorter.

Wherever you are, the geometry is the same: a primary rainbow forms opposite the sun while the sun is less than about 42 degrees above the horizon. Bowcast's research-informed heuristics give extra weight to clearing showers. The gauge above applies them to ensemble forecasts for the 12 km around Fort William.

Rainbow questions, answered

When do rainbows appear in Fort William?
Rainbows need sunlit rain with the sun lower than about 42 degrees, so in Fort William useful windows often occur after sunrise or before sunset on showery days. A study in ZhaoSu, China found that about nine in ten observed rainbows occurred during the hour after rainfall. Bowcast uses that regional finding as research guidance, not a universal rate.
Where should I look for a rainbow in Fort William?
Always directly opposite the sun: put the sun at your back and look toward the retreating rain. In the evening that means looking east; in the morning, west.
What is the estimated rainbow chance in Fort William today?
Bowcast checks about 40 forecast ensemble members for sunlit-rain ingredients around Fort William, hour by hour, for the next 7 days. The result is an estimated chance from model agreement, not a probability calibrated against observed rainbow frequencies. This page shows today's peak and best forecast interval; the Now board shows the interval containing the current time.

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