SAN DIEGO (KSWB) — The Southwest U.S. monsoon season officially begins this week, and will impact parts of California, Colorado, Utah, Arizona and New Mexico.

According to the National Weather Service, June 15 through Sept. 30 is the recognized time period for severe weather in the geographic region.

A monsoon explained

Oftentimes, when we think of monsoons we associate them with torrential downpours and mudslides. Though this isn’t necessarily inaccurate in some areas of the world, what describes a monsoon is more simple: the shifting of the season to summer. The word monsoon actually comes from the Arabic word mausim, which means “season.”

So, a monsoon isn’t an individual thunderstorm or rainstorm, but rather a large-scale weather pattern that causes summer thunderstorms, NWS explained. They are caused by a seasonal shift in the winds.

Why do winds shift? Well, NWS says the temperature of the land and the temperature of the water are different as seasons change — in this case, as spring becomes summer.

To break that down further, monsoon winds always blow from cold temperature to warm. Land warms up faster than bodies of water at the beginning of summer. Therefore, warm air rising off the land creates conditions that reverse the direction of the wind — a monsoon.

The diagram below, which was created by the National Oceanic and Atmospheric Administration, shows how seasonal temperature differences between the land and ocean can create the right conditions for a monsoon.

How monsoon season affects the Southwest U.S.

When it comes to the Southwest U.S., the monsoonal flow develops as a strong area of high pressure aloft that NWS says is centered over the Four Corners region.

Basically, the monsoonal flow draws in warm, moist air from Mexico into the Southwest U.S. which then produces thunderstorms. The effects of this weather, according to weather officials, are generally more prominent from Arizona eastward.

NWS says these thunderstorms mainly occur in mountain and desert areas, but can also occur in the valleys and coastal areas.

Hazards to watch out for during monsoon season

Bouts of heavy rain during monsoon season can create flash flooding. NWS describes a flash flood as “a rapid flow of high water into a normally dry area, or a rapid water level rise in a stream or creek.” Weather officials have warned that even just 6 inches of surging flood water has the capacity to knock over a grown adult.

As a further warning for drivers, NWS says just 12 inches of rushing water can carry away most cars, while 2 feet of rushing water can carry away SUVs and trucks.

Here’s what weather officials say you should do if hear that a Flash Flood Warning has been issued for your area:

• Be alert and watch for rising water.
• Go to higher ground immediately.
• Don’t drive where water covers the road.
• Never attempt to cross a river, creek or stream of unknown depth, especially during times of flooding.

More flood safety tips and resources can be found here.