How come in the summer time it progressively gets warmer everyday vs the wintertime I can be 40 degrees one day and 80 the next?

Like in the summertime it's almost always 90 degrees or higher, but in the winter the temps vary so much like it could be 40 degrees one day and 75 the next.
How come in the summer time it progressively gets warmer everyday vs the wintertime I can be 40 degrees one day and 80 the next?
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