In Central Texas it does not get that cold. For winters I just use a "Breathable Nylon Wind Breaker" with a hood (Anorak type). I then pile on appropriate layers underneath for the temperature. Even then, temperature regulation was inadequate till I sewed in some arm pit zippers. Its not pretty but it gives me a comfortable temperature range to ride in 40's° to 60's° F.
I know... For some people that's T shirt weather... Ha
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No matter where you're at... There you are... Δf:=f(1/2)-f(-1/2)