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For other uses, see Portal (disambiguation).
A Portal Storm is an event that creates a multitude of portals to other dimensions. As suggested, these portals spread devastating shockwaves outwards in a storm-like manner, causing havoc wherever they hit.
Since the Resonance Cascade at Black Mesa, Portal Storms have occurred all over the world bringing forth life forms from Xen. This peculiar phenomenon is generally capable of inflicting severe structural damage to objects, such as buildings and bridges. A Portal Storm consists of a blue "wave" which resonates from a source portal and moves across the landscape, negating gravity as it goes. As a result, any object in its path would suffer damage from the brief weightlessness effect.
At Black Mesa East, Eli Vance keeps a corkboard with several newspaper cut-outs, one of them features the header "Portal" Storm Continues, this entry is next to a paper about the Seven Hour War, leading to the belief that the Combine exploited these storms to invade Earth.
During the Uprising, a series of Portal Storms originating from the ruins of the Citadel ravage the surrounding landscape. Shortly after experiencing one, Alyx Vance remarks that it was "like the first days all over again." This suggests that Portal Storms were most frequent in the first few years after the Black Mesa Incident or the Combine invasion and, with time, they became more infrequent; meaning that they have not stopped entirely and are still happening erratically.