In "Every Little Hurricane" from Sherman Alexie's The Lone Ranger and Tonto Fistfight In Heaven, what two things collide and cause the storm?

In the story "Every Little Hurricane" from Sherman Alexie's The Lone Ranger and Tonto Fistfight in Heaven, brothers Adolph and Arnold ("High-pressure and low-pressure fronts") fight in Victor's front yard creating a metaphorical hurricane. This story is told from a third-person limited point-of-view following the thoughts of Victor, who is a boy in this story (he's older in other stories in this collection).

The entire story is an extended metaphor comparing the plight of the modern Native American living on a reservation to the damage that can be created by a hurricane. This fight between brothers, although it causes major damage, is nothing large on an Indian reservation. According to the narrator, "One Indian killing another did not create a special kind of storm. This little kind of hurricane was generic. It didn’t even deserve a name."

Although this storm started with the brothers fighting, it was transferred from Indian to Indian at this party. The narrator discusses several of the terrible memories the party's guests have primarily because they are Indian. Victor's father remembers being spit on while he waited for a bus; Victor's mother remembers the Indian Health Services doctors sterilizing her without permission after she gave birth to Victor; the brothers remember their other battles during childhood because "[w]hen children grow up together in poverty, a bond is formed that is stronger than most anything. It’s this same bond that causes so much pain." 

Victor sees all these things happening—the negative feelings, the feelings of resentment—and continues to compare them to a hurricane:

"The forecast was not good. Indians continued to drink, harder and harder, as if anticipating. There’s a fifty percent chance of torrential rain, blizzardlike conditions, seismic activity. Then there’s a sixty percent chance, then seventy, eighty."

In the morning, all was good, but the Indians, "the eternal survivors, gathered to count their losses."

This extended metaphor suggests that what happens on an Indian reservation—alcoholism, violence—isn't caused by men, but, like a hurricane, is an outside force that is beyond the control of the people, but leaves tremendous damage in its wake.