Reading weather for photography

"Sunny" is a useless word

A cloudless noon is one of the hardest skies to shoot. The light is harsh, the sky is a blank, and there's no tonal depth. A day forecast as "cloudy, turning overcast" might give you ten minutes of fire in the sky, because the cloud base is low and the gaps are narrow.

The icon answers whether to take an umbrella. We want to know what the light will look like. So skip the icon and read the numbers.

Seven numbers that matter

1. Cloud cover and layers

As a rule of thumb, 30 to 70 percent low and mid-level cloud is the best bet for sunrise and sunset. There's cloud to catch the low light, with gaps to let it through. No cloud gives a clean but flat gradient. Total thick cover is usually just grey.

Layers matter more. High cirrus takes colour well, mid-level altocumulus gives you texture, and thick low cloud mostly blocks.

2. Cloud base

Often ignored, and crucial in the mountains. If the cloud base is below your position, you're inside the cloud and will see nothing. If it sits just above the peak you're shooting, you may get cloud pressing down on the summit. Compare the two numbers before you climb.

3. Visibility and air quality

Visibility decides how much contrast is left in the distance. Above 10 km, far layers can look clear. Below 5 km, anything more than a kilometre or two away turns to grey. It tracks air quality closely, which has its own guide.

4. Dew point spread

More useful than relative humidity is the gap between air temperature and dew point. The smaller it is, the closer the air is to saturation. A gap of 0 to 2 °C with little wind often means morning fog. Above 5 °C, fog is unlikely.

It also warns you about your lens. A cold lens taken out of a warm car will almost certainly fog up.

5. Wind

Wind blurs branches and water in long exposures and shakes the tripod. It also sets how fast the clouds move, which decides whether a longer exposure will streak them. On coasts and ridges it's usually much stronger than the forecast for the flat ground nearby.

6. Sun times, blue hour and golden hour

Think of these as four periods, not two moments.

These shift a lot with latitude and season. A high-latitude summer can stretch blue hour past an hour, while a low-latitude winter may give you twenty minutes. Go by the actual local times.

7. Chance of rain

"40% chance of rain" means about a four-in-ten chance of measurable rain somewhere in the forecast area. It doesn't mean 40% of the rain. Short showers are often more worth going out for than steady drizzle. The ten minutes after the rain clears give you washed air and the best visibility and colour of the day.

Three habits for reading forecasts

Read the trend, not a single hour. An exact hour three days out means nothing. "Clearing around Wednesday" does. Check the hourly forecast 6 to 12 hours before you leave.

A forecast is a grid value, and your spot is a point. Valleys, lake shores and urban heat islands all pull the real weather away from a grid point a few kilometres off. Treat 500 m of altitude difference as a different place.

Finish with radar and satellite. A last look at live radar and which way the cloud is moving beats any hourly table.

Ten minutes before you leave

1. Sun times, to fix the window you're aiming for.
2. Cloud cover and cloud base, to see if there's a chance and whether you'll be swallowed.
3. Visibility and air quality, to choose between distance and something close.
4. Dew point spread, for fog and for keeping your lens clear.
5. Wind, to plan tripod, filters and shutter speed.
6. Rain timing, so you have a plan for when it clears.