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high, low

Hyphenate as compound modifier preceding a noun; do not hyphenate following a noun unless in Webster's:
           the high-energy photon was observed
           the knee-high muck surrounded us
           he stood knee-high in shavings
           low-density sprawl
but     the cartons were stacked three high
           that was a low blow
Lowercase for a weather system:
           the Aleutian low
           a low weather system
           a Bermuda high