Getting spectacular shots of towering
thunderclouds or churning seas is all about watching the elements
‘Professional weather photographers use
hourly meteorological data and rainfall radar to predict and chase storms into
the perfect position for a shot.’
Look at any landscape photography
competition and you’ll see how the right weather can bring drama to your
photos. Winners of the $15,000 Take A View 2011 landscape photography awards,
for example, captured storm waves exploding in a Guernsey bay, brooding
thunderclouds over a Scottish salmon fishery, and a motorbike ride in glorious
sunshine. But how do you shooting fleeting cloud formations, rough seas and
violent storms while minimising long waits and wet equipment? The trick is to
understand and predict the weather.
Autumn
Landscapes
Knowing how to find interesting clouds is a
great way to liven up the skies in your photographs, and clouds form by three
main processes. The first is simple convection, which creates fair-weather
cumulus clouds and heavy summer showers. Cumulus clouds look like large ball of
floating cotton wool, and they can produce really attractive images because
they have well-defined outlines and impressive clearly-visible structures.
Cumulus form as the sun warm the ground,
which heats overlying air and makes it lighter than the surrounding cool
atmosphere. A bubble of warm air rises, expands and cools – a process called
convection – to from an invisible air column, or thermal. Cooler air holds less
water than hot air. A cumulus cloud is born when the air column cools enough to
drop, or condense, its excess water onto floating dust or ice crystals. A good
time to spot cumulus is a few hours after dawn on clear days, especially in
summer. They scatter as the sun’s heat wanes at dusk.
A single cumulus billows upwards until be
rising air loses heat, energy and buoyancy, and it disperses after about 15
minutes. Look for cumulus above strongly sunlit round, such as south-facing
slopes in the northern hemisphere. Sometimes cumulus clouds also spawn above
forest fires or power station cooling towers.
Heavy afternoon showers are likely if
cumulus clouds grow fuzzy cauliflower-shaped turrets on a spring or summer
morning. These clouds are swelling into enormous cumulonimbus thunderheads.
Cumulonimbus are classic storm clouds that can produce rain, lightning and
hail. They develop when there’s abundant hot, moist air and wind speeds
increase with height. Air rising through the thermal is blown sideways, which
sucks additional warm air upwards at wind speeds of up to 113km (70 miles) per
hour. The taller the cloud, and stronger the updraught, the more water can
condense and the heavier the rain. A cumulonimbus grows until the rising air
cools to the temperature of the surrounding environment. If the cumulonimbus
reaches the top of the lower atmosphere, the cloud spreads sideways into an
anvil shape facing the wind direction.
Spectacular-looking mammatus clouds are
occasionally found beneath cumulonimbus anvils. Air bubbles begin to sink, and
warm, as the anvil spreads sideways, causing the moisture in the bubble to
evaporate. Evaporation cools the air, making it descend faster. When the
bubbles reach the cloud base, they drag it down into pouch shapes.
Air streaming from the anvil can also form
feathery high clouds called cirrus. Falling ice crystals buffeted by
fluctuating winds create the clouds’ wavy-brushstroke shapes, nicknamed mare’s
tails. Cirrus can be spotted ahead of a cumulonimbus anvil.
Photograph cumulus and cumulonimbus a few
miles to one side to capture their billowing vertical structure and the
cumulonimbus anvil. Shooting beneath a cumulonimbus cloud can be dangerous
because of the high winds, lightning and heavy rain. Look for mammatus towards
the back of a storm. Use a super wide-angle lens for shots with a foreground or
a zoom lens for close-ups of mammatus pouches, and face the west at sunset to
shoot mammatus with an orange glow behind them.
A second good place to spot clouds is on
mountain sides and hillslopes. When moist air blows over a hill, it cools and
water condenses into clouds. If condensation occurs below the peak, mist or
hill fog forms. Lenticularis clouds have dramatic streamlined shapes, rather
like UFOs, and sometimes form in fair weather on the downwind side of hills.
The air continues oscillating up and down after passing over the hill. When it
bounces up, it cools and forms clouds.
In temperate regions, such as the UK, huge
weather systems called cyclones or depressions also cause clouds and rain.
Depressions affecting the UK generally form over the North Atlantic and are
steered from west to east by winds. At a depression, huge masses of similar
temperature air rotate around an area of rising air. Cold air masses affecting
the UK typically come from northern Canada and the Arctic Ocean. Warm air
masses come from the tropics. After three to 10 days, the cold air pushes
beneath the warm air and lifts it off the ground,
The depression’s warm front is where the
warm-air mass slowly rises over cold air, producing wide sheets of cloud.
Cirrus and cirrostratus clouds form more than 600km (373 miles) ahead of the
warm front. Cirrostratus are high ice clouds that form a thin, translucent
layer which veils the sun and can create stunning optical effects, such as mock
suns or ice halos. As the warm front nears, the clouds lower and thicken from
mid-level altostratus clouds into low grey stratus. These cloud sheets reduce
visibility and produce steady rain that extends perhaps 240km (150 miles) before
the front. As the warm front, passes, the rain stops, although the sky remains
overcast.
At the cold front, cold air forces warn air
upwards, forming a narrow band of cumulonimbus called a squall line. Cirrus and
cirrostratus stream ahead of the storm clouds. Cumulus is often found behind
the cold front. Wind direction changes and visibility improves once the cold
front has passed.
Local weather reports on the internet, TV
and radio provide clues about good clouds to shoot. You may find isolated cumulonimbus
separated by patches of clear sky when the forecast is ‘bright spells with
showery rain. Heavy thundery showers are possible’.
You can predict country-wide weather from
surface pressure charts on websites like BBC Weather. The curved lines on these
charts are called isobars, and link locations with equal atmospheric pressure.
Pressure is measured in units called millibars (mb) or hectopascals (hPa). One
millibar equals one hectopascal. The UK’s average atmospheric pressure is
around 1013hPa, and rarely rises above 1050hPa or falls below 950hPa.
Sinking air pushes downwards on the ground,
increasing air pressure and creating high-pressure areas. These bring clear
days because descending air stifles cloud formation. Rising air reduces air
pressure on the ground. Low-pressure areas are associated with rainfall and
depressions. The closer the isobars, the bigger the pressure change, and the
faster air is rising. Tightly-packed isobars suggest strong winds and violent
storms.
Some professional weather photographers use
specialist meteorological data, updated hourly or less, to track cumulonimbus
into the perfect position for a shot. They pre-select good vantage points in
non-storm conditions, such as mountain or wide-open fields, and drive there
when they forecast a storm.
