Nature Photography journal
Reading a forecast for light rather than for weather
The forecast tells you whether it will rain. Four other fields tell you what the light will do.
A weather forecast is written for people deciding whether to take a coat. Almost everything that predicts good light is in the fields nobody reads.
Cloud cover percentage
Zero per cent gives hard, contrasty light and an empty sky. It is the worst forecast for landscape work and the one most people treat as good.
A hundred per cent gives flat, even light with no direction and a white sky. Excellent for woodland detail and for foliage colour, useless for anything depending on modelling.
The interesting number is between about thirty and seventy. Broken cloud means shafts, moving pools of light on a hillside, and a sky with structure in it. This is where almost every memorable landscape frame is made.
Cloud base
Published in most aviation and mountain forecasts and almost never in general ones, which is why the mountain forecast is worth finding.
A base below the summits means the tops are in cloud: no distant view, but the possibility of ridgelines appearing and disappearing, which is its own subject. A base just above them means dramatic light on the tops. A base at several thousand metres means the cloud is decoration rather than an event.
Visibility
Landscape depth comes from atmospheric haze, and haze is visibility. Perfect twenty-kilometre visibility flattens a valley into a wall of equally sharp ridges. Moderate visibility separates the planes and gives you the layered look that makes distance legible.
You want less visibility than a pilot does.
Frontal timing
The best light of a week is very often in the hour after a front clears. The air behind a front is clean, the cloud is breaking, and the low sun gets under the departing edge.
That means reading when a front passes rather than whether it rains. A forecast that says rain until four and clearing after is a better forecast than one that says dry all day.
What none of this tells you
Whether it will actually happen. Marginal fog forecasts fail more often than they succeed, and the good light lasts twenty minutes rather than the two hours the forecast implies.
The practical consequence is that the number of mornings you go out matters more than the accuracy of your reading. Read the fields above to decide which mornings are worth it, then accept that half of them will not work.