With 53-Across, weather phenomenon with trapped warmth, and a hint to this puzzle's circled letters (4)

I believe the answer is:

heat

(Other definitions for heat that I've seen before include "Energy that caues a rise in temperature" , "Warm up" , "Preliminary round in a contest" , "Pressure" , "Warmth - gossip mag" .)

I've seen this clue in The Wall Street Journal.

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