Las Vegas Sun

July 22, 2019

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What to expect from this monsoon season and beyond

moonsoon

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If you think the weather has been weird recently—a lot wetter and cooler than usual—it’s not just in your mind. This has been the rainiest start of the year since 2005. The average annual rainfall in Las Vegas is 4.19 inches; we already reached 4.51 inches by May.

Fact check

Some people are afraid that a chilly spring means a hotter summer. Here’s the truth: Gorelow says that more cloud cover because of El Niño could lead to higher average temps in the summer—not because the highs are higher, but because the clouds keep the nightly lows warmer. Think of the clouds as a blanket on the city that keeps the heat in.

For insight into this wacky weather, as well as the latest predictions, we spoke with Andy Gorelow, a meteorologist for the Las Vegas branch of the National Weather Service. Gorelow has been watching the weather in the Vegas Valley for about 20 years.

“It has been wetter and colder than normal across much of the West Coast,” Gorelow says. Because of the El Niño pattern, storm systems that have usually moved toward the Pacific Northwest are staying south and bringing that cooler, wetter weather.

The mechanics of monsoon season

• Short Answer: Heat + Moisture = Thunderstorms

• Long Answer: During non-monsoon season, weather patterns move from west to east, so most of the Las Vegas Valley’s precipitation is coming from the Pacific Ocean. In the winter, the city receives more gentle rain that lasts longer.

During the summer, the desert heat creates a high-pressure system that settles in the Four Corners region. It pulls up moisture from the Gulf of Mexico and the Gulf of California, which creates big, heavy thunderstorms. The storms dump a lot of rain in a short amount of time, causing flash flooding.

Las Vegas has it [relatively] easy. Southern Nevada is actually at the northern outskirts of the North American Monsoon range. Typically, Arizona gets the worst of monsoon season because it’s even hotter down there and because it’s closer to sources of moisture. Whereas Las Vegas may get monsoon conditions every few days, Arizona can get it every day.

Twenty years of Vegas weather

What to expect from this year’s monsoon season

Gorelow says it’s hard to tell this early out, but don’t be surprised if we continue to experience above-normal precipitation.

Some people are afraid that a chilly spring means a hotter summer. Here’s the truth: Gorelow says that more cloud cover because of El Niño could lead to higher average temps in the summer—not because the highs are higher, but because the clouds keep the nightly lows warmer. Think of the clouds as a blanket on the city that keeps the heat in.

The biggest changes in temperature during the past 20 years are because of the urbanization of the desert, which creates a heat island effect. The average temperatures are going up, but that doesn’t mean we’re seeing more 120-degree days. The highs have stayed pretty much the same, but the overnight lows are not as low, according to Gorelow. The official climate station for the National Weather Service happens to be at McCarran International Airport, which is the center of town. Gorelow says that if you were to measure the outskirts or Pahrump, the average temperatures won’t have increased quite as much.

All about El Niño

We can expect this unusual weather to last through the summer and even into the fall, according to Gorelow. He says it’s hard to tell quite yet whether this pattern will affect monsoon season. The prediction is for normal to above-normal precipitation through summer and fall.

We’re officially drought-free!

Don’t duck, don’t cover

Midwest tornadoes are making the national news. Fortunately for us, they’re part of a completely separate weather system. So tornadoes are one thing Las Vegans don’t have to worry about.

For years, it rained so rarely in Las Vegas that locals were said to store their windshield wipers at home to keep the rubber from drying out. Those days are over—for now, at least. Gorelow says there is not one spot in Nevada that’s in drought. He doesn’t see “anything over the next year that’s going to put us in a drought.”

How Weather Service meteorologists get it done

Their main job is to forecast the weather in order to protect life and property. At the Las Vegas office, they put out seven-day forecasts for Southern Nevada, Northwest Arizona and Southeast California. Meteorologists make the forecasts using a variety of tools, from weather balloons to weather models. For a wealth of weather info, visit weather.gov.

How a weather balloon works

Meteorologists launch helium weather balloons at 4 a.m. and 4 p.m. daily from their Las Vegas office. A radiosonde is attached to the balloon, and it measures temperature, wind, pressure and relative humidity. Many weather offices around the world launch balloons at the same time (some are even launched off ships in the ocean). The global data is gathered in a super computer in Washington, D.C., which is used to generate weather models.

This story originally appeared in the Las Vegas Weekly.