Southwest monsoon activity to bring daily rounds of showers and thunderstorms

Amid expansive drought conditions in place across the southwestern United States, the onset of the seasonal monsoon conditions will bring along some relief to the region over the coming week. Although an uptick in moisture will be welcome by those living across the Southwest, some storms will feature a unique set of potential hazards in the coming days.

Each year at around this time, the southwestern United States, normally known for its low humidity, experiences a change in wind direction that pumps higher levels of moisture into the region. This occurs due to an area of high pressure that sets up to the southeast of the area.

The flow around this area of high pressure transports moisture northward from the Gulf of Mexico and the eastern Pacific Ocean. This phenomenon, known as the North American monsoon, is arriving right on schedule this year.

Historically, most cities across the Southwest have a major increase in the amount of rainfall observed between the months of June and July courtesy of the onset of the monsoon, and this year will feature just that. On average, Phoenix only averages 0.02 of an inch of rainfall during the month of June, but as the monsoon kicks into gear, the city receives just over an inch of rain on average during the month of July.

Through early week, afternoon shower and thunderstorm coverage is expected to remain relatively limited to the high terrain across much of the Southwest. Given the steering winds present in the atmosphere, rainfall will continue to struggle to make it into the lower valleys. But, as a weak disturbance takes aim at the California coastline into midweek, increased levels of moisture will blanket the Southwest.

While the atmosphere will contain more moisture than it typically does at other times of the year in the Southwest, not all of the thunderstorms bring beneficial rain. This can especially be true for thunderstorms that are beginning to fall apart. When that occurs, strong winds are dragged downward from the collapsing thunderstorm.

Such a scenario can cause dust storms, known as haboobs. Visibility can rapidly drop to near zero and practically turn day to night in the most intense haboobs. Motorists must be cautious for these events when traveling.

While there may be a chance for a few of these haboobs through early week, there may be a better chance for this atmospheric phenomena later in the week.

Another unsuspecting hazard that can threaten the southwestern United States is the risk of "dry thunderstorms". Sometimes if the air mass near the surface is dry enough, rain falling from a thunderstorm can evaporate prior to hitting the ground.

Unfortunately, lightning will still travel to the surface regardless if the raindrops make it there or not. If this occurs, these lightning strikes can spark new wildfires. This can be especially concerning because dry thunderstorms can often contain strong wind gusts that could quickly fan the flames.

With the expected increase in moisture across the Southwest mid- to late week, some of these threats may be realized as thunderstorms explode over the region.

Regardless of what any of these storms produce over a given area, the increase in clouds will cause temperatures to be somewhat lower than recent days. Therefore, the entire region will benefit from the monsoon in that respect.

The atmospheric pattern through the latter half of the week would suggest that monsoon activity will fire up daily, even bringing along a chance for wet weather across the lower valleys at times. By the upcoming weekend, moisture could spread northward across the Intermountain West, bringing a widespread threat for showers and thunderstorms.

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