|Forecasting Dust Storms in Iraq
As a weather forecaster each place you forecast for in the world is different. All areas have their own unique
forecasting challenges. In the country of Iraq you would think that your challenge would be; how hot is it
going to be today? Although this is usually what most people ask about when you get into discussions of
weather in Iraq, the real challenge is dust storms! I prefer to call them dust events because when I
think of a storm I think of something that lasts only an hour or so where these dust events can last
for days. As soon as you put a dust storm in your forecast, the following three questions follow:
when will you get them, how often will they last, and how will it effect day to day operations
especially in a military environment?
There are basically two types of dust storms, the haboobs and the shamals. Haboobs are hard to forecast for
due to the way they form which is from an outflow boundary of a thunderstorm. These events occur during
the late fall to spring seasons and are also the most dramatic of the two because they happen so fast.
This is the type of dust storm that looks like a wall of water speeding toward you only it is dust. For
aviators it is a nightmare and would surely end with unfavorable consequences. For people on the
ground it would go from daylight to total darkness in a matter of minutes. Haboobs move in quickly,
but also move out fairly fast.
The second dust event and the one that I will spend the rest of this document discussing is the shamal
dust storm. This type of dust event isn't as dramatic as the haboob, but it does cause reduced visibilities.
Shamal dust events are caused by persistent northwest winds blowing over a source region and picking
up dust into the atmosphere. These events are not as sudden as the haboob, but it can last much longer.
Shamals can last from four to fives days during one event.
The first thing you need to look at when forecasting a shamal event, is source regions. Most source regions
are located in the lower Tigris and Euphrates river valleys. They can also be smaller deposits located in
or near dry streams or lakes in Iraq. There are also a large number of source regions in Iran, just on
the eastern border of Iraq. The consistency of the dust in these areas is similar to talcum powder;
this is why we call it a dust storm rather than a sand storm. Also keep in mind areas where
construction is going on. These areas will cause localized dust events that can significantly
reduce visibilities, but only affecting a small area like a city.
The biggest reason for knowing these source regions is predicting if you forecasted winds are going to
tap into these source regions and lift the dust into the air causing a dust event. Depending on the
wind direction will determine where the dust will go. If the winds are from the north or northwest,
then the area to the south and southeast of the source regions will be affected. If the winds are
blowing from the south or southeast, then the areas to the north and northwest will be affected.
These northerly winds can also tap into the source regions in Iran.
During spring and summer months in Iraq the winds are mainly from the north northwest, therefore
areas in the middle to southern portions of Iraq, such as Balad and Baghdad have visibilities
reduced to less than 1600 meters by these dust events approximately 5% of the time. Where Tallil
has visibilities reduced to less than 1600 meters 20% of the time due to is location further
southeast with many source regions to the north and northwest. Areas to the North and northeast
such as Mosul and Kirkuk are only reduced 1% of the time to less than 1600 meters. From late
fall into early spring the winds are reversed and therefore the areas affected are reversed also.
During the summer months the 300 mb pattern changes from a westerly winter flow with migratory lows
moving through to a pattern dominated by high pressure light and variable winds, the result no clouds
and no rain. This makes the source regions primed for dust to be lifted into the air. Closer to
the surface you have winds called shamals, which mean north in Arabic, blowing from northwest.
These winds last all summer long and are also called "the winds of 120 days." These winds are
created from the interaction between the Pakistani Heat Low and the high pressure ridge over
the Mediterranean which extends into northern Saudi Arabia. This interaction results in a
pressure gradient set up and winds increasing in speed. These winds can last one to ten days
and usually reduce in speed at night.
Due to radiationial cooling at night an inversion sets up with surface winds less 10-15 knots. Above
the inversion a low level jet develops and can get as strong as 60 knots. When the inversion is broken
and the wind is mixed down to the surface you can expect dust. The wind speed needed to suspend dust
is 15-20 knots. Winds of 30 knots downstream of a source region can reduce visibilities to
practically nothing. Things to look at are the night skew-T sounding. If it shows 30 knots
of wind at 1,000 feet you might want to think about dust in the morning. Look at models and
if they are forecasting 30 knots of wind at 1,000 feet during the night from the northwest
and you are southeast of a source region, you really might want to think about dust. One
thing to keep in mind is that as wind mixes down the speeds reduce so don't think because
you have 30 knots at 1,000 feet you are going to get 30 knots at the surface when it mixes
down. As the night goes on look at upstream stations and watch there observations for
winds and visibilities. They will be your first indicator of what is to come. This may
be your only way of timing the dust to arrive at your area. This also may be your
only way of knowing it is out there in the early morning hours while it is still dark.
One of the things that make the shamal dust events so hard to forecast is the fact that they form
overnight and into the early morning hours and the best way to see them is with visual satellite
imagery. As everyone knows there is no visual imagery at night; therefore you feel blind when
trying to see what is going on around your location. Keep in mind dust is very thin and sometimes
can't even be seen on visual satellite imagery. When looking a visually imagery don't be fooled
by how thin dust looks because even thin plumes of dust can reduce your visibilities significantly.
Infrared imagery does not show dust very well and therefore isn't a big help when it comes to
forecasting dust events. Another thing that makes it tough to forecast is that the dust
is normally in a plume pattern. Because of this you might have a location to your west
that is socked in with dust and your location is clear with no reductions to visibilities.
These plumes start off small and narrow from the source region and the further the distance
from the source region the wider they become. Of course the closer you are to the source
region the thicker the dust and the lower the visibilities will be. Depending on
wind speeds these plumes of dust can reach as high as 15,000 feet in the atmosphere.
They average 3,000 to 8,000 feet and normally reduce visibilities
between 4800 and 8000 meters.
The effects of dust storms vary depending on who you talk to. If you talk to civilians in Iraq they
would say that they are just a hindrance and other than having to protect their faces to keep the dust
out of their eyes and lungs. For military ground troops it affects daily operations of searching for
terrorists and also protecting themselves and others from terrorists. The people it affects
the most is aviators. Dust storms affect all types of flying operations. When you have a dust
storm you can't get fighters in the air to protect those that need it, medivac units can't take
off to help those in need, and for those who are already in the air, it can prevent them from
landing in a safe place or landing period. Dust also has adverse effects on any equipment that
is consistently going through these storms. Extra time cleaning and protecting equipment is
necessary. Areas that are prone to dust storms can also prevent people from
using certain equipment.
You can receive climatologically data from the 14th Weather squadron, formally known as the Air Force
Combat Climatology Center. They have narratives on dust storms in Iraq. I think better night time
satellite imagery would help to forecast shamal dust events better. As for haboobs being able to
better forecast where thunderstorms will occur is the only improvement to finding possible areas
where haboobs may occur. So as you can tell weather forecasters have a very important job. It
is demanding and imperative that we give the best forecast possible. It can save lives.
14th Weather Squadron in Asheville, NC
Michelle Moses - forecaster at Balad Air Base, Iraq
28th OWS Shaw AFB, SC