Monsoon Dust Storm- Haboob
Phoenix has been in the news the last month or so due to the amount of dust storms we have been experiencing.
A dust storm is a meteorological phenomenon common in arid and semi-arid regions. Dust storms arise when a gust front or other strong wind blows loose sand and dirt from a dry surface. Fine particles are transported by saltation and suspension, a process that moves soil from one place and deposits it in another.
The term sandstorm is used most often in the context of desert sandstorms or places where sand is a more prevalent soil type than dirt or rock, when, in addition to fine particles obscuring visibility, a considerable amount of larger sand particles are blown closer to the surface. The term dust storm is more likely to be used when finer particles are blown long distances, especially when the dust storm affects urban areas.
Our local weather people are now calling dust storms a haboob.
Haboobs, derived from the Arabic word "haab," which means wind or blow, typically hit during the desert Southwest's monsoon season, in which thunderstorms can drop deluges of rain onto the parched desert.
A haboob is a type of intense dust storm carried on an atmospheric gravity current, also known as a weather front. Haboobs occur regularly in dry land area regions throughout the world.
During thunderstorm formation, winds move in a direction opposite to the storm's travel, and they move from all directions into the thunderstorm. When the storm collapses, and begins to release precipitation, wind directions reverse, gusting outward from the storm and generally gusting the strongest in the direction of the storm's travel. Haboobs can also form when a strong thunderstorm weakens rapidly, and releases a microburst.
When this downdraft of cold air, or downburst, reaches the ground, it blows dry, loose silt and clay (collectively, dust) up from the desert, creating a wall of sediment that precedes the storm cloud. This wall of dust can be up to 100 km (62 mi) wide and several kilometers in elevation. At their strongest, haboob winds often travel at 35–100 km/h (22–62 mph), and they may approach with little or no warning. Often rain does not appear at ground level as it evaporates in the hot, dry air (a phenomenon known as virga). The evaporation cools the rushing air even further and accelerates it. Occasionally, when the rain does persist, it can contain a considerable quantity of dust. Severe cases are called mud storms.
"On July 9, 2018, the massive dust storm that blew through Phoenix was unquestionably epic, and it may even have been historic. The haboob at times towered about a mile high and traveled nearly 200 miles, carving a path from the Arizona desert into southeastern California. The average dust storm usually dies out after about 25 or 50 miles.“From what I’ve heard, it’s probably in the top two,” National Weather Service meteorologist Bianca Hernandez said. “The storm chasers were saying it was similar to the big one in 2011.”Hernandez was referring to the much talked about, massive July 5, 2011, dust storm that seemed to swallow the city. However, she could not say whether Monday’s dust storm, which fizzled out near Imperial, Calif., set a record." Another weatherman estimated this particular haboob traveled around 250 miles. During these events, the dust-laden winds can sometimes hit 80 to 100 mph. Some past haboobs have traveled some 400 miles with dust reaching up to 6,000 feet high. "They can be quite hazardous if you're on the road — it can be lights out, and you can’t see five or 10 feet ahead."
Tonight's dust storm or haboob was not extreme but I tried to take pictures as it approached our house so those of you not familiar with a dust storm could see how it approaches.
If you look closely, you can see a plane. I know they closed Shy Harbor Airport so I hope the plane is leaving the area and not trying to land.
This dust storm today wasn't that powerful but AAA suggests you do the following if you are caught in one.
"Dust storms are common in Arizona and usually occur between May and September. The most intense storms occur during the late summer months known as monsoon.
Dust storms can create dangerous, sometimes even deadly driving conditions and sometimes reduce visibility to zero. The area between Tucson and Phoenix is noted for being the only place in the United States to experience the "haboob," a raging dust storm that travels across the desert at 50 to 60 mph.
AAA says drivers need to be especially careful when they get behind the wheel of a car and practice safe driving habits so they don't find themselves "at one" with a large tree or worse, another vehicle.
If you run into a severe dust storm, reduce the speed of your vehicle immediately and drive carefully off the highway. After you are off the paved portion of the roadway, turn off your vehicle's lights to ensure other cars do not follow you off the road and hit your vehicle. Wait until the dust storm had passed before getting back on the highway. If you are walking or riding your bike, get inside quickly or seek shelter.
Here are some other tips to help drivers safely maneuver through the Valley during a monsoon storm:
Reduce speed and turn on driving lights
Pull off the roadway
After you are completely off the traveled portion of the roadway:
Turn off driving lights
Keep your car radio on
If you are on the freeway, leave the freeway at an exit ramp, if possible.
Wait until visibility is at least 300 feet before re-entering the roadway.
Heavy rain may follow the dust storm.
If you see a dust storm forming in the distance, exit the roadway immediately."
The Arizona Department of Transportation recommendations:
Straight lines winds in a thunderstorm can lift huge clouds of dust and reduce visibility to near zero in seconds, which can quickly result in deadly, multi-vehicle accidents on roadways.
Dust storms are more common in the early part of the monsoon, near agricultural areas, and near Willcox Playa in Cochise County. Use caution in these areas any time thunderstorms are nearby.
Dust storms usually last a few minutes, and up to an hour at most. Stay where you are until the dust storm passes.
Avoid driving into or through a dust storm. If you encounter a dust storm:
Immediately check traffic around your vehicle (front, back and to the side) and begin slowing down.
Do not wait until poor visibility makes it difficult to safely pull off the roadway -- do it as soon as possible. Completely exit the highway if you can.
Do not stop in a travel lane or in the emergency lane. Look for a safe place to pull completely off the paved portion of the roadway.
PULL OFF! LIGHTS OFF! FOOT OFF!
If you encounter a dust storm while driving, pull off the road immediately.
Turn off your headlights and taillights, put your vehicle in "PARK," and take your foot off the brake (so your brake lights are not illuminated.) Other motorists may tend to follow taillights in an attempt to get through the dust storm, and may strike your vehicle from behind.
Stay in the vehicle with your seat belts buckled and wait for the storm to pass.
Drivers of high-profile vehicles should be especially aware of changing weather conditions and travel at reduced speeds.
Know the emergency plans for your area.
Familiarize yourself with these terms to help identify a dust storm hazard.
Dust Storm Watch—Tells you when and where dust storms are likely to occur. Watch the sky and stay tuned to NOAA Weather Radio, commercial radio or television for information.
Dust Storm Warning—Issued when visibility is 1/2 mile or less due to blowing dust or sand, and wind speeds of 30 miles an hour or more.
Research additional information on dust storms, beginning with the following resources.
National Weather Service
Pull Aside, Stay Alive