Portal-storm

The "Portal Storm" (sometimes referred to as the Ark Storm) is the swirling mass of clouds that can be observed above the Ark Portal, outside New Mombasa in the levels Tsavo Highway and The Storm. It can also be seen on computer screens in the level Crow's Nest.

1st Appearance
The Storm was first seen in the Halo 3 announcement trailer. When the camera shows the artifact being uncovered & activated, the storm lies directly over it. Lightning bolts are seen flashing out of the clouds. The formation seems to have an eye, like a hurricane would. When the portal is activated, the beam travels up through this eye and disappears.

Formation
In the level Crow's Nest, when a player looks up at some of the computer moniters, you will see a map of the local area. The map will have a mass of clouds beginning to show a swirling motion around the area. When you enter the level Tsavo Highway, you can see a donut-shaped mass of clouds above the artifact that the Covenant are digging up. When you proceed to the level The Storm, which is named after (presumably) the storm above the portal, The storm has intensfied and grown. The clouds now bring rain to the area, and certain parts of the cloud glow as if cloud-to-cloud lightning is occuring. When Truth activates the Portal, the solid blue beam shoots up into the cloud formation's eye and opens the portal to the Ark.

Dissipation
After the portal is opened, and the level Floodgate begins, the remains of the clouds are seen broken up and swirling around the portal in the sky, having been disrupted by the opening of the portal itself.

Artificial or Real?

 * The Storm above the portal may be an artificial storm, created only by the activation of the Ark Portal. The Forerunners could create weather on Halo, so why not on Earth?
 * The storm may also be a natural hurricane, and may just have appeaed over the portal by coincidence. The ocean is not far from the area, and it may have formed over the ocean and moved over the portal.

Trivia

 * At a point in the level The Storm, a group of marines are standing around listening to a radio. Intel comes over the radio and says "...winds inside the storm have been clocked at over 200 kilometers per hour."