The negative form of "extreme"

A common antonym of extreme, in contexts ranging from weather to politics, is moderate:

ODO:

  • Average in amount, intensity, quality, or degree.   ‘we walked at a moderate pace’
  • (of a person, party, or policy) not radical or excessively right- or left-wing.   ‘a moderate reform program’

American Heritage Dictionary:

  1. Being within reasonable limits; not excessive or extreme:    a moderate price.
  2. Not violent or subject to extremes; mild or calm; temperate:  a moderate climate.
    • Of medium or average quantity or extent.
    • Of limited or average quality; mediocre.
  3. Opposed to radical or extreme views or measures, especially in politics or religion.

Macmillan Dictionary:

    neither very great nor very small in amount, size, strength, or degree
    Cook the spinach over a moderate heat.
    A moderate earthquake shook the San Francisco bay area this afternoon.
    We need more housing for moderate-income families.
    This is a new drug for treating mild to moderate depression.