Why Does it Storm After a Hot Day?
Heatwave conditions create ideal conditions for thunderstorms to form. Lightning strikes and thunder blasts are created when different electrical charges accumulate in clouds, air or the ground.
Warm air rises until it meets cold air, where it cools and condenses to form water droplets which then combine with each other to form the towering cumulonimbus clouds that mark thunderstorms.
Warm Air Rising
As air warms, it expands, taking up more space. This causes molecules to move more slowly, using up less energy and thus lowering air pressure, making it easier for air to rise. Rising air then cools off on its journey up, producing condensation (precipitation) as it cools, creating clouds and moisture as condensation (precipitation) forms, leading to clouds and moisture formation – an act which produces wind on any scale from local gusts to global winds belts circling Earth.
The phrase, “heat rises,” provides an accurate depiction of how air currents work. Hot air is lighter than cold air, causing it to rise above denser cold air masses and provide much of the energy behind weather systems such as rainstorms, hurricanes and tornadoes. When rising warm air collides with mass of colder air masses it may collide into it, pushing against them along a front that produces thunderstorms — known as a warm front.
Water Vapor Condensation
Water vapor in the air is an integral component of the water cycle. Water molecules spread much further apart when in its gaseous state than they would when solid form, but as it cools it condenses back down into liquid form – providing us with fog, raindrops on car windows on humid days, and moisture which causes glasses to fog when taken from an air-conditioned room and put in another cold room.
Water vapor must have somewhere to condense onto in order for clouds to form, and millions of microscopic particles called condensation nuclei serve as platforms for it. When the dew point is reached, these condensation nuclei serve as platforms where condensed water vapor condenses onto them – these might include salt, clay minerals or solid pollutants such as sulfates and nitrates – heat energy is transferred between vapor molecules and nuclei and surface tension drops decrease significantly.
Cumulonimbus clouds produce thunder and lightning when air rises rapidly in response to warming, as their rapid ascent causes water droplets to freeze into ice crystals that rub against each other, giving off positive and negative electrical charges which gather at different locations within a cloud; positive charges tend to gather near its top edge, while negative ones collect near Earth or other clouds causing strong charges to collect and attract each other, eventually discharging and producing thunderclaps of sound.
These particles, called Ice Nucleating Particles or INPs, play an essential role in cloud formation, impacting precipitation levels and climate via changes to how much sunlight the cloud reflects. Scientists are working hard to better understand their formation and their abundance/distribution. A recent review article by Susannah Burrows from PNNL Earth Sciences provides an overview of what we know about INPs as well as where knowledge gaps and modeling gaps still exist.
Lightning strikes when the negative charge at the base of a cloud builds up enough strength to attract positive charges on the ground – this occurs because opposites attract. Ice particles flying through clouds rub against each other creating electricity which builds until their difference creates enough of an imbalance for them to connect and discharge a lightning bolt.
Lightning heats the surrounding air rapidly, producing an explosive shockwave we hear as thunder. It may appear in different colors depending on what it comes into contact with in terms of haze, dust or raindrops in its path – including what happens in terms of cloud cover, raindrops or any other objects present.
Lightning flashes from storms may be visible up to 100 miles away, yet only 10 or 15 miles of thunder may be audible due to refraction and reflection – sound vibrations being refracted off of low density troposphere atmosphere and back towards your ears.