Dust Storm!

We have a lot of dust in Niger. In a previous blog, I talked about the harmattan. This is the dusty wind that can blow off the Sahara any time during the long dry season (October-May). It is especially bad in December through March. See the dust that collected on our windowsill in a two-week period in March below:

This time I want to talk about dust storms (or sand storms, as they're sometimes called). At the end of the dry season, there is a three-month period of time called the hot season (mid-March to mid-June). This is a time of intense heat and rising humidity as the monsoon winds begin to blow in from off the ocean to the south and west and work themselves in under the upper-level winds which keep blowing from off the Sahara. Towards the end of the hot season, small storm cells begin to form as the hot, humid air rises into the atmosphere, creating towering cumulus clouds. These storms can be extremely violent, with high winds, hail, and pelting rain that accumulates at a rate of more than an inch an hour.

The high winds in these storms pick up all he loose dust, which has very little to hold it down, and throw it hundreds of feet into the air. The result is a huge wall of orange or black dust preceding the storm. It comes rolling in like a tsunami. Sometimes we joke that weather predicition in the Sahel consists of watching for the dark dust cloud on the horizon and knowing that when you see it, you have about ten minutes to get your laundry in off the line before it hits. The dust storms can turn night into day, and they can blow for as long as an hour. Rain may or may not follow the dust storm, but the dust storm is always associated with the rain clouds, and there will be rain somewhere even if you don't get it. In one dust storm, you can see as much dust settle on your windowsill (and tables, chairs, desktops, computers, etc) as you see in two weeks of harmattan dust like in the picture above.

I wrote about these dust storms backin 2004. I'm going to paste in what I wrote here:

"Few things are as spectacular or as dramatic as a sandstorm in the Sahel region of Africa. For days on end during the months of April and May, the heat and humidity build as the monsoon winds blown in from off the ocean. When you feel like you can't stand it one minute longer, and sweat is pouring down your legs and off your face, you know a storm is not far off. A dark line of clouds appears on the horizon, and you run to shut all the windows in your house, knowing that you have 15-30 minutes at most to prevent your house from becoming a disaster area.
As the storm clouds approach, a bright orange "fog bank" appears ahead of the storm. This is the sandstorm, which boils out in front of the rainclouds. The fierce winds pick up the fine Sahara sand and throw it hundreds of feet into the air, creating a massive orange cloud of dust that gradually gets bigger and bigger as it approaches. As you watch it coming, the air is still and close. Suddenly, the sandstorm hits, and the winds increase to gale force knocking down trees and branches and carrying away anything light with them. The dust sandblasts your face and skin, and the day becomes dark and gloomy. Sometimes there is so much sand in the air that the sky becomes black as night. The sandstorm may last anywhere from 5 minutes to an hour. The temperature drops dramatically, often as much as 30 degrees fahrenheit in the space of five minutes. After the sandstorm passes, the rain begins. Huge thunderclouds unleash their reservoirs of water, and torrents of rain begin lashing the ground. Within an hour, an inch or two or rain may fall. After the storm all is cool and still, and the smell of the rain settling the dust perfumes the air. "

We've had two big dust storms this past month in Tera. We had our first on May 6. That one was rather weak and only turned the sky a milky orange. It wasnt' terribly windy, either. The areas surrounding Tera got a lot of rain that day, however. We got about 0.15 inches in town. The next day, Monday, May 7, we had a doozy of a dust storm, one that turned the sky into almost night at 4 p.m. Here is a picture of the approaching wall of dust.

We didn't get any rain after this dust storm, but it was cooler for a day or two. We did get 0.75 inches of rain on May 13, however. That was in the night, and it didn't have a huge

dust storm with it, just a lot of wind. That night was really cool. We haven't seen any rain in Tera since May 13, and the rainy season hasn't officially started yet, but some parts of the country have already been blessed with good first rains. Once the rains get going, they settle the dust down, and the dust storms don't blow any more.

I'll leave you with a picture looking out our window around 4 p.m. on Monday, May 7, 2007.

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