Las Vegas Sun

September 19, 2018

Currently: 87° — Complete forecast

5-MINUTE EXPERT:

Anatomy of a thunderstorm

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Steve Marcus

Lightning strikes behind Las Vegas Strip casinos as a thunderstorm passes through the northwest valley Wednesday, Sept. 13, 2017.

Knee-deep in monsoon season, the Las Vegas Valley is trending slightly above average for precipitation during the desert’s wettest time of the year. According to the National Weather Service, rainfall for June at McCarran International Airport was nonexistent through the entire month, but July outputs of .78 inches nearly doubled the annual average for that month.

Lightning Storm passes through the Northwest Valley

Lightning strikes to the northwest of downtown Las Vegas as a thunderstorm passes through the valley Wednesday, Sept. 13, 2017. Launch slideshow »

“There’s a high pressure system moving across the northwest that’s bringing moisture up from the Gulf of Mexico,” NWS Meteorologist Jenn Varian explained.

With clouds and precipitation come thunderstorms, to which the Valley has not been a stranger this summer. Here’s a look at the science behind the sky’s natural electric blasts:

The thunderstorm equation: Moisture + lift + unstable air

The three basic components required for a thunderstorm to form are moisture, lift and unstable air. As warm, moist air rises in an updraft, it transfers heat from the earth’s surface to the upper levels of the atmosphere in what’s known as convection.

The water vapor in the air begins to cool at higher elevations, releasing heat and condensing to form a cloud.

The cloud continues to grow and move upward to altitudes where temperatures are below freezing, forming ice particles that grow in size as they join with other water vapor.

Eventually, the ice particles become too heavy to be held up by the rising air and begin falling, creating a downdraft of cool, dry air and rain.

How does lightning form?

Two kinds

A thunderstorm is a rain shower in which you hear thunder. As thunder comes from lightning, all thunderstorms have lightning.

• Dry thunderstorm/heat storm: A thunderstorm in which precipitation evaporates before hitting the ground.

• Severe thunderstorm: A thunderstorm with hail that is at least the size of a quarter (1 or more inches in diameter) and includes either wind gusts of 57.5mph or greater, or a tornado.

Ice particles collide with one another, creating an electrical charge. Lots of similar collisions build up big regions of electric charge, causing a bolt of lightning. Lightning creates sound waves known as thunder.

How hail forms

Hail forms when thunderstorm updrafts are strong enough to carry full water droplets well above the freezing level. The freezing process forms a piece of ice known as a hailstone, which gets larger as additional water freezes onto it. The hailstone eventually becomes too heavy for the updrafts to support it, and it falls to the ground.

Spotting a thunderstorm

Cumulonimbus clouds are generally known as thunderstorm clouds. High winds will flatten the top of the cloud into an anvil-like shape. Cumulonimbus are associated with heavy rain, snow, hail, lightning and tornadoes. The anvil usually points in the direction the storm is moving.

• The day before: Look for cirrostratus clouds. The sheetlike, thin clouds normally cover the entire sky and are visible 12 to 24 hours before a thunderstorm.

• The morning of: Look for altocumulus clouds, which are grayish and white, with one part of the cloud almost always significantly darker than the other. Altocumulus clouds take shape in groups.

Watches and warnings

• Thunderstorm watch: If a severe thunderstorm is possible for an area, the NOAA/NWS Storm Prediction Center will issue a severe thunderstorm or tornado watch, meaning residents should watch and prepare for severe weather and stay tuned to weather media outlets to know when warnings are issued.

• Thunderstorm warning: If a severe thunderstorm is imminent, the local weather service branch will issue a severe thunderstorm or tornado warning, meaning there’s a serious threat to life and property to those in the path of the storm, per the National Severe Storms Laboratory, and those affected should act immediately to find safety and shelter.

• Red flag warnings: Issued by NWS, red flag warnings are used to inform area firefighting and land management officials that weather conditions are ideal for the combustion and rapid spread of fire.

How does it feel to be struck by lightning?

Depends on who you ask. Participants gave different accounts to media outlets about the severity and pain of being struck by lightning, but almost all described the experience as unpleasant, involving soreness and temporary loss of motor skills. More than 20 percent of people who are struck by lightning die, according to the National Oceanic and Atmospheric Administration. About 47 people in the United States die each year after being struck, the administration said.

What happens if lightning strikes your car?

The metal frame of your car directs lightning currents to the ground, but vehicles are usually damaged when hit by lightning. Lightning travels around the surface of the vehicle, then to the ground.

Henderson microburst

On July 20, gusts of wind reached 70 mph, and nearly .75 inches of rain fell over Henderson during an hourlong storm, according to the National Weather Association. The microburst resulted from a localized column of sinking air within a thunderstorm to produce a massive storm. A microburst thunderstorm is “like a big ball of rain, wind and rain-cooled air that hits the surface of the earth and pushes out, sometimes in one direction and sometimes in all directions,” explained Kate Guillet, a weather service meteorologist. “They’re not uncommon during monsoon season,” she added.

This story originally appeared in the Las Vegas Weekly.