1. Sahara Means “The Greatest Desert” in Arabic

The Sahara is appropriately named, as it is the largest hot desert in the world. It covers the northern third of Africa and is comparable in size to countries such as the United States, Canada, and China. Much of the desert is uninhabited. Rain is nearly non-existent, with the Sahara averaging about 20 millimeters (0.8 inches) of rain per year. Its residents live on the coast and on the far outer fringes of the desert. Sand temperatures over 80°C (176°F) have been recorded in the Sahara.

There are no roads across the Sahara, but a 4,500 km (2,800 mi) Trans-Saharan Highway that runs north/south from Algiers, Algeria to Lagos, Nigeria is in the works. A few brave people have successfully driven across the Sahara in a 4×4, but it is considered one of the most dangerous drives in the world.

2. Violent Sand Storms are a Routine Occurrence in the Sahara

The Sahara’s latitude aligns it nearly perfectly with the strong easterly trade winds that blow across the Atlantic. When violent sand storms are lifted by heating, convection, and turbulence that occur naturally over the desert, they cross paths with the trade winds. As a result, ejections of massive plumes of dust over the eastern Atlantic Ocean occur routinely. When the dust plume is large enough and the trade winds are strong enough, Saharan dust can reach North America, which is happening right now.

3. Geologists Can See Deposits of Saharan Dust in North American Soil that Dates Back Thousands of Years

While the levels of dust can vary wildly from year-to-year, dust events follow a fairly routine schedule. The presence of Saharan dust can be seen in the layers of soil samples taken in North America, South America, and the Caribbean, as well as sediment samples taken from the bottom of the Atlantic Ocean.

These studies give scientists a glimpse into not just geology, but also meteorology, climatology, oceanography, and human behavior thousands of years ago. The area right off the coast of Mauritania, Western Sahara, and Senegal is one of the most studied areas in the world for deposits of Saharan dust.

Do you want to know something else really cool these studies have uncovered?

4. Every 20,000 years, the Sahara Cycles Between a “Desert Sahara” and a “Green Sahara”

Every 20,000 years, there is a wobble in the Earth’s orbit. As a result, a dramatic shift in the tropical monsoon occurs over Central Africa. The next time this happens, the monsoon will shift dramatically to the north, dumping lots of rain across the Sahara Desert. As more rain falls, trees, shrubs, and other vegetation start to grow. Eventually, lakes and ponds form too. The Green Sahara can resemble anything from a tropical swamp like you’d see in the Florida Everglades to a dense jungle like you’d find in parts of South America or Southeast Asia to a lush savannah or grassland like the ones that are currently in Kenya or Tanzania.

Proof of the Green Sahara Starts with Saharan Dust

Now come on, there’s no way that just some dust deposits at the bottom of the ocean can prove this. You’re right that the dust alone doesn’t prove this. When combined with archaeological and anthropologic evidence found in the Sahara, it does. Every 20,000 years, there is a significant reduction in dust deposits as vegetation in the Green Sahara holds the soil and place, preventing the massive sand storms that are common across the Desert Sahara. In some of the most uninhabitable places of the current Sahara, archaeologists have found paintings depicting the Green Sahara, as well as fossils of both tropical jungle plants and marine life. Even mangrove fossils and whale fossils have been found in the middle of the Sahara.

When is the next shift of the Sahara?

So are we going to see the Green Sahara in our lifetimes? Unfortunately, no. The last change from Green Sahara to Desert Sahara occurred about 5,500 years ago, so there’s still about 15,000 years to go until the next Green Sahara starts. Even if the changeover were to start tomorrow, it usually takes between 100 and 200 years to transition between the Desert Sahara and the Green Sahara.

Before we shift back to the current Saharan Dust storm, here’s one more fun fact about the Green Sahara. The drying of the Sahara as it underwent its most recent shift from Green Sahara to Desert Sahara 5,500 years ago led to the rise of the Ancient Egyptian Civilization.

5. The Current Saharan Dust Storm is Suspended at an Elevation of Approximately 1.5 to 6 Kilometers (5,000 to 20,000 Feet)

In the Sahara, when strong winds whip up sand storms, strong heating, convection, and turbulence that occur naturally over the desert lift the dust and sand particles high into the atmosphere, reaching altitudes as high as about 6 km/20,000 feet. The lift from that heating and convection is so strong that the dust particles get up in the jet stream. The dust then rides the jet stream across the Atlantic.

I know what you’re wondering. Why doesn’t the dust just fall out of the sky? What keeps it suspended in the air? There are two possible scenarios.

1. You can think of the atmosphere in terms of layers, just like layers in a cake. The jet stream is above the ground layer, and can be several layers above that ground layer. As the plume of dust moves west across the Atlantic, the ground layer often has a thermodynamic makeup that blocks particles from entering it from above and prevents dust particles from settling back down.
2. If you look at a vertical profile of the atmosphere, you will find areas of lift and areas of subsidence. Strong jet stream winds encourage lifting in the atmosphere, which keeps the dust particles suspended aloft, much like raindrops in a cloud.

Gravity will eventually win this battle. Once the dust gets blown into weaker upper-level winds or out of the jet stream completely, it will begin to settle.

6. The Current Saharan Dust Storm Will Primarily Impact the Eastern United States

The southeastern United States, as well as Puerto Rico and the Virgin Islands will see its greatest effects. The main effect you’ll see is just a thick haze. If you’ve ever been near a wildfire, it will look very similar to that, just without the smoky smell.

The latest weather observations show very strong trade winds blowing from east to west across the Caribbean. A high pressure system sits just off the east coast of Florida, which will pull the dust north through the Gulf of Mexico. Not surprisingly, the states seeing the greatest impacts of the dust include Texas, Louisiana, Mississippi, Alabama, and Florida.

Models show the dust plume will continue north across the Mississippi River valley. It will then shift east, impacting much of the central and eastern United States. The high pressure off the coast of Florida will slowly shift to the east over the next couple of days. At that point, it will pull the dust back into Florida. Ironically, the US state closest to the Sahara, Maine, will likely the least impact, at least among the eastern states.

Now, what does that mean for those of us who live west of the Great Plains? There is a strong wind blowing across Central America and up the west coast of Mexico. Miniscule amounts of Saharan dust may reach the far southern parts of California, Arizona, and New Mexico. Any effects will be so minimal that you will barely notice.

7. You May Notice Adverse Health Effects, Especially in the Southeastern US, Puerto Rico, and the Virgin Islands

If you’re experiencing symptoms similar to allergies or a very mild cold, such as sneezing, coughing, runny nose, scratchy throat, or itchy eyes, the dust is likely at least partly responsible for it. Even if you’re not allergic to anything in it, the dust is still an irritant that can cause these symptoms. When I am exposed to excessive amounts of desert dust here in Arizona, I tend to sneeze a lot and get scratchy throats.

If you are sensitive to low air quality, there are a few things you can do to limit your exposure:

• Close your windows and doors and stay indoors
• If your air conditioning has a recirculate mode, use it
• Avoid being outdoors for extended periods
• The masks you wear to stop the spread of COVID-19 will help reduce irritation from the dust. N95 respirators will filter out the dust particles, but the regular cloth masks are better than nothing.

8. The Dust Will Produce Spectacular Sunrises and Sunsets

Light refracting through particles suspended in the air equals beautiful colors at sunrise and sunset. That’s just simple physics.

9. The Saharan Dust Will Temporarily Pause the Atlantic Hurricane Season

Many people think that the dust somehow interferes with the sunlight or the heating necessary to form hurricanes. That is incorrect. When the Sahara ejects dust plumes over the Atlantic, it also ejects very dry desert air along with it. The dust plume stays in that pocket of very dry air as it makes its journey across the Atlantic.

When the dust gets to the Caribbean, the very dry air that it is traveling in is strong enough to cut off the moisture supply that tropical cyclones require in order to form. Extremely dry air, such as that found in deserts, is impressively difficult to re-humidify, so once the dust leaves the area, it will take several days for moisture to return to its normal levels.

Further inland, you will also see the same effect. The only difference is that the dust will be shutting off rain and thunderstorms, not hurricanes.

10. It is Full of Nutrients that Allow Plant Life and Agriculture to Flourish

Saharan dust is so much more than “just dust”. In fact, Saharan dust is a type of mineral dust that is extremely rich in nutrients such as iron and phosphorus, which fertilizes and gives life to some of the lushest forests on the planet. In the Amazon rainforest alone, the Sahara deposits over 22,000 tons of dust every year, making it almost solely responsible for keeping the Amazon’s ecosystem so healthy and lush. Because the Amazon gets so much rain, if it weren’t for the Saharan dust, the Amazon’s nutrients would wash away very rapidly.

Saharan dust deposits in the ocean are a bit more of a mixed bag. While they deliver the same benefits they bring to ecosystems on land, the mineral-rich dust can also be a breeding ground for algae blooms and red tides, which can release toxins and deplete the ocean of oxygen, resulting in mass death of ocean creatures. I experienced several red tides back when I lived in the Tampa Bay area of Florida. Trust me, they are not pleasant to be near.

11. The Current Saharan Dust Storm in North America is Not a Haboob

You have probably heard the word “haboob” thrown around as massive dust storms barrel across the deserts of the American Southwest during the summer monsoons. The Saharan dust plume is not a haboob. Let me explain.

Do you know the saying that all squares are rectangles, but not all rectangles are squares? The same analogy applies here. All haboobs are dust storms, but not all dust storms are haboobs. So what exactly is a haboob?

A haboob is a specific type of intense dust storm that is carried on a weather front. In North America, they are almost exclusively found on gust fronts and outflow boundaries as monsoon thunderstorms collapse. They are a routine occurrence in the deserts of the southwestern United States and northern Mexico during the summer monsoon. The word “haboob” is an official meteorological term that means “blasting” or “drifting” in Arabic.

How exactly does the Saharan dust storm differ from a haboob? Let’s have a look.

12. Does It Affect the COVID-19 Pandemic?

Not in a major way. The dust plume will not be in one specific location long enough nor be severe enough to have any significant impacts on the pandemic. You may see a very slight uptick in hospitalizations for a day or two. The Saharan dust will have little to no effect on case counts or death counts.

If you’re currently ill with COVID-19, a cold, or any other respiratory illness, the dust plume may exacerbate your symptoms for a day or two. Staying inside with the doors and windows closed will help mitigate that exacerbation.

13. The Saharan Dust Storm is Impacting Many More Countries than just the United States

The current Saharan dust storm will likely impact over 50 countries by the time it’s all said and done. In the map below, countries shaded in red will see effects of the Saharan dust. It wouldn’t surprise me one bit if the dust finds its way into to additional countries. Nations in Central America and the Caribbean, as well as the southeastern United States will see the greatest effects of the dust.

If you have any questions about this unique event, please leave them in the comments. I’ll answer them as soon as I can.

Until next time.

Top Photo: One of the largest haboobs in Arizona history near Gila Bend, Arizona – July, 2018

The post Saharan Dust Storm: 13 Surprising Ways It Might Impact You appeared first on Matthew Gove Blog.

Before we begin, here’s a quick overview of the geography and how the monsoon storms work. The blue line is the approximate dividing line between the flat, low desert and the mountains, most of which range from about 3,000 to 7,000 feet above sea level. A very common setup in the summer is for storms to form over the mountains as air at the surface is forced up, and then the storms roll off the mountains, gaining momentum as they go downhill (just like a ball rolling downhill), and then come ripping across the desert floor. The storms last night did exactly that. In the radar loop later in this post, take notice of how the storms really start to accelerate very close to where the blue line of the map below, especially along the US-60 corridor, which runs northwest from Phoenix.

Shortly after sunset last night, the skies began to darken to our north and east as a line of severe thunderstorms rolled off the mountains. The first thing that hits with these storms is a haboob, which is a powerful dust storm that forms on the gust fronts/outflow boundaries in thunderstorms. When you’re sitting at home, dust storms are harmless, but they drop visibilities to usually less than 1/4 mile.

A haboob from a very similar storm 48 hours earlier approaches from the east

The haboob last night was even more eerie, as you could see the cloud-to-ground lightning strikes in it more and more prominently as it approached. As the sunlight faded into twilight, the winds increased further, and visibilities continued to drop. My weather station, which currently gathers its data from Lake Pleasant measured a maximum sustained wind of 60 km/h (37 mph) during the storm, but gusts at my house and throughout the area were much higher.

Now, when I say I have a suspicion that we were hit by a small tornado, you need to understand that the conditions I was working in allow it to only be just a suspicion. The video below was shot about 10-15 minutes before the suspected tornado hit. As you can see, daylight is pretty much gone, and we were in the middle of a huge dust storm. You could not see anything.

Around 8:30 PM, my first hint of a possible tornado was that the potted plants that I keep on a table on my back patio started elevating. I was able to get some of them inside before the mayhem started, but not all of them. The pots on these plants are the cheap plastic ones that don’t weigh anything and are about 6-8 inches in diameter. Perfect for becoming projectiles and missiles in this exact scenario. As I was coming back out to rescue the last few plants, I watched as the pots were sucked right off of the bottoms of at least 2 or 3 of the plants and out from underneath my covered patio before being thrown over the house and into the night.

My “garden” during more tranquil conditions

It was about right then that I was beginning to realize that standing outside like that probably wasn’t the smartest thing to do, so I retreated back into the safety of my living room. No more than about 5 seconds after I closed the door we were hit by a huge wind gust, which I estimated to be in the 120-130 km/h (75-80 mph) range. It was immediately followed by another gust of equal intensity, but in the exact opposite direction before the wind let off and returned to the direction it had been blowing. I have been scraping my brain all day, and still have yet to come up with something other than a small tornado that can explain that. By about 9:15 PM, the outflow boundary had gotten far enough out in front of the storm to cut off its fuel supply, so it began to rapidly weaken.

I got up this morning with one purpose: to try to find some evidence that had been left behind to support the theory of a tornado. A walk around the house revealed no damage to the house itself, other than a few of my covers for my external outlets were missing. When I lived in Oklahoma, looking for evidence of tornadic winds in trees and grasses was pretty straight forward. Doing it in a desert landscape like this is a whole other ballgame.

Barren Sonoran Desert landscape that would prove to be a challenge for finding evidence of a small tornado.

I wandered across the street and into the desert in the approximate path I though a possible tornado would have taken. I found a patch of grass that had been blown down in all different directions, but it’s next to impossible to say whether the storm did that or not. About 200 to 300 feet from the house I found a dead plant that I had been using as a marker in my back yard. It certainly could have been picked up by a tornado and dropped there, but it could have blown down there in straight-line winds, too. I eventually found my outlet covers, some of which were over 500 feet from the house, but the flower pots could not be recovered.

Despite all of the flower pots flying over the house, there was one instance where the plant completely vanished and the pot was left untouched.

The other telling sign of a possible tornado I found was back at the house. Inside of my grill stand, where the propane tank lives, I had wedged an empty plastic bottle way in the back corner behind the tank where there was no possible way it could just blow away in regular wind. I had noticed during the storm that the door on the grill stand got sucked open at one point, and when I looked there this morning, that plastic bottle was no where to be found.

So at the end of the day, did we have a tornado? It’s certainly possible, and maybe even likely, but I don’t have enough evidence to definitively say either “yes, we had one” or “no we didn’t”. We were hit by the end of the squall line that is most likely to produce tornadoes as it bows out, but finding evidence of small tornadoes even in the most ideal landscapes is challenging. Regardless, it’s been a wild few days, and I look forward to what the remainder of the monsoon has to offer over the next month or so.

In the next post, we will analyze some of the meteorological data from Lake Pleasant for this event. I’ll leave you with the radar loop of the entire event (watch how the storms accelerate as they come off the mountains and approach US-60 NW of Phoenix), courtesy of the National Weather Service in Phoenix.

The post Wild Night of Monsoon Storms and Possible Tornadoes in the Desert appeared first on Matthew Gove Blog.

This phenomenon is called a haboob, which is a very specific type of intense dust storm that forms on strong outflow boundaries or gust fronts of thunderstorm. They are often caused by air rushing out of a thunderstorm during a microburst or when the storm’s updraft collapses. They can be up to 100 miles long, 2 miles high, and frequently pack winds in excess of 50 mph, which can reduce visibilities to near zero in an instant.

The term haboob is an Arabic word that originated in the Sahara regions of northern Africa, but is an official meteorological term that has used throughout the world for almost a century. A haboob is a very specific type of dust storm, so all haboobs are dust storms, but not all dust storms are haboobs. If you’re still confused and would prefer to just call it a dust storm, that’s perfectly fine.

This past Monday, I was down at the Organ Pipe Cactus National Monument to view some wildlife and explore some of the ranching history at the monument. I knew it was going to be an active monsoon day, but I never would have guessed that it would have turned into such an incredible afternoon of storm chasing almost by accident. We “chased” 2 dust storms, including the one haboob, and numerous thunderstorms from the Mexican border all the way back to Phoenix.

Monsoon thunderstorms begin to bubble up along the US-Mexico border east of Lukeville, AZ

Shortly before leaving the Organ Pipe Cactus National Monument, skies began darkening to the east as the monsoon storms started initiating over the nearby mountains. I wanted to start heading north in order to stay ahead of the storms, as that would offer the best photo opportunities.

Sitting just outside the northern boundary of the national monument is the town of Why. It’s a small and mostly forgotten town whose inhabitants today are mostly US Customs officers and Border Patrol agents. As I passed through town, I looked in the mirror and it looked like the mountains to the south were disappearing into thin air. The first dust storm of the day was here.

First dust storm of the day swallows the nearby mountains as it heads for the town of Why, AZ

I don’t think this first dust storm qualified as a haboob because it was a long way from the thunderstorms that had popped up and was unlikely that it was traveling on an outflow boundary or gust front. Second, it lacked the “wall of dust” property that defines haboobs, but passing over the mountains may have disrupted the appearance of being a wall of dust.

The 50 mile run from Why back to Gila Bend was uneventful. Back in Gila Bend, a quick look at the radar show that nearly the entire Phoenix metro was under a Severe Thunderstorm Warning, with a line of severe thunderstorms stretching most of the way down to the Mexican border. I knew that we were going to run into something along Highway 85 between Gila Bend and the I-10. The question was what. Was it going to be torrential rains? Flash flooding? Extreme winds? Dust storms? Hail? Intense lightning? There was only one way to find out. We turned north on Highway 85 and didn’t look back.

As skies rapidly darkened as we headed north, I was hoping that we would just see some heavy rain, as there was no evidence of dust storms on radar, but in the back of my mind I knew these were textbook conditions for monster dust storms.

The other issue that needed to be resolved fast was the issue of sheltering in the event of hazardous weather. Lightning and flash floods were my top concerns, since that is all wide open flat desert without any trees, hills, bridges, or anything else to hide under or on. Dust storms were also a concern because side roads to pull off on are few and far between along that stretch of highway, and just pulling off the highway is risky and dangerous at best.

As we continued north, I began to notice something underneath the thunderstorm that didn’t look quite right. There was definitely something underneath it, but it wasn’t rain, and was the wrong color to be hail, which left blowing dust as the remaining possibility. Blowing dust is a common occurrence in Arizona, especially during the summer, so I didn’t think much of it, and kept heading north. Less than five minutes later, we came around a bend in the road that passed through a little cut in the mountains, and when the terrain opened back up, that’s when it set in. Holy crap, that’s a massive haboob I’m driving straight at.

Strange color under the thunderstorm on the left side of the frame. Can you see the haboob?

The exact moment I realized: Holy crap, I’m driving straight into a giant haboob.

There are two things that make dust storms so dangerous when you’re driving: how hard is the wind blowing inside of it, and what is the visibility inside of it? On the roads, you really have to assume that the visibility will drop to zero if you drive into it, so getting off the highway and pulled off on one of the side roads was the next challenge.

When you’re driving 70 mph towards a haboob that’s already moving 30-50 mph at you, it’s amazing how fast it closes on you. As I looked for a side road to pull off onto, the wall of dust got closer and closer by the second. It only took about a minute or two before all I could see in front of me was the wall of dust.

Approaching the haboob. Do you see any side roads to pull of onto?

Running out of time to find a place to pull off.

Just as the wall of dust was about to swallow us, I saw a left turn lane in front of me. I couldn’t believe it. It was a side road into one of the shooting ranges in the area. I turned down it, and pulled off into a dirt turnoff/parking area less than 100 feet down the road, still facing north. I hadn’t even had a change to put the truck in park yet when the haboob hit, and it hit hard. Winds inside the dust storm were easily gusting over 50 mph, and while visibilities didn’t go completely to zero, they dropped to less than 100 yards pretty much instantly. You could see the far side of Highway 85, but that was about it.

Inside the haboob along Highway 85, looking southeast after visibilities started improving.

Thankfully, the haboob was moving fast enough we only had to wait about 20 minutes for conditions to improve enough to continue driving home safely. The haboob ended up swallowing the entire southwestern quadrant of Arizona over the course of the evening, and there were some absolutely breathtaking images of it as it approached the Yuma area. I lost track of it once it crossed into Mexico, but it was certainly a dust storm for the ages, and one of the coolest experiences I’ve had in a while.

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