As monsoon gets underway across the Southwest, you may be wondering – what exactly is it?

Monsoon is a period from June 15 to September 30 that brings with it thunderstorms, flash flooding and more.

This meteorological season is marked by a shift in the primary wind flow from the west or northwest to the south or southeast. This change in wind direction bring with it moisture from the Pacific Ocean and the Gulf of Mexico.


Monsoon storms are powered by intense surface heat – thanks Arizona summer – and an influx of moisture from the south.

Fun fact: Monsoon thunderstorms generally occur when the temperature in the Valley is between 100 and 108 degrees, according to Arizona State University.

Monsoon storms can produce dangerous conditions, including:

• Flash floods

• Strong winds

• Lightning

• Thunderstorms and dust storms

RELATED: Here's how you can protect your home

The beginning of monsoon brings the extreme heat and raises the wildfires risk, while storms generally follow.

Key terminology

Watch: Widespread severe weather is possible but not imminent

Warning: Life-threatening weather is about to occur or has been reported

Flood Advisory: Heavy rains will cause minor flooding (will be upgraded to Flash Flood Warning if conditions worsen)

Downburst, macrobust, microburst: Localized pockets of intense downdrafts – or strong downward rushes of air. Large ones are called macrobursts and measure at 2.5 miles in diameter and have damaging winds that last 5 to 20 minutes. Microbursts are smaller are generally last 2 to 5 minutes.

Dust devil: Vortex of dust filled air created by extreme surface heating. Diameters of dust devils range from 10 feet to more than 100 feet. They are generally between 500 and 1,000 feet tall, but can be taller.

Outflow: Air that flows outward from a thunderstorm. Here's a more detailed explanation.

Monsoon: A thermally driven wind arising from differential heating between a land mass and the adjacent ocean that reverses its direction seasonally.

Heat lightning: Lightning you can’t hear because it’s too far away. This describes when you see a lightning strike in the distance but never hear thunder, which only has an audible distance of about 20 miles.

Dry lightning: Also called a dry thunderstorm. A microburst with little or no precipitation reaching the ground. Dry microbursts may develop in an otherwise fair-weather pattern. At the ground, the only visible sign might be a dust plume or a ring of blowing dust beneath a local area of virga.

Virga: Streaks or wisps of precipitation falling from a cloud but evaporating before reaching the ground. In certain cases, shafts of virga may precede a microburst.

One word we don’t use

When it comes to dust storms, you’ve probably heard people use the word haboob. That’s not a term 12 News uses when referring to dust storms in the Valley because ours aren’t generally intense enough. Here’s a full explanation.