This article contains spoilers. Read at your own risk!
It might spoil your gaming experience when first playing the related games.
A Portal Storm is a randomized event that creates a portal to another dimension.
The Combine may have come to or at least learned about Earth through the portal storms. Since the resonance cascade at Black Mesa, portal storms have occurred all over the world, teleporting in life forms from Xen. In addition, portal storms are capable of inflicting severe structural damage to objects such as buildings and bridges. They consist of a blue 'wave' which resonates from a source superportal and moves across the landscape, apparently negating gravity as it goes.
While in Black Mesa East, the player can see a newspaper cut-out that says '"Portal" Storm Continues'. As this is next to a paper about the Seven Hour War, this could be a sign that the Combine used these storms to invade Earth.
In Half-Life 2: Episode Two, a series of portal storms seeming to originate at the Citadel ravages the surrounding landscape. Shortly after experiencing one, Alyx Vance remarks that it was "like the first days all over again", hinting that portal storms were most frequent in the first few years after they started, and then perhaps became infrequent. This could be from a permanent Combine Teleporter within the Citadel. After the Citadel's destruction it is likely the Combine had to revert back to Portal storms to move troops between worlds.
Notes and references
- ↑ Alyx Vance: "It's like the first days all over again..."
|Quantum event(s)||Portal Storm · Resonance Cascade · Sprite · Superportal · Teleportation|