Create cross sectional plots for a function of two variables?

Questions
1

I have attached a notebook with the function I am trying to model and understand.

Temperature_Function.nb (462 KB)

2

I don’t understand what you mean exactly. Try playing with PlotRange:

F[t_, x_] := 30*Cos[(2 Pi/365) t - 0.211728 x]*Exp[-0.211728 x] + 35
Plot3D[F[t, x], {t, 0, 365}, {x, 0, 70},
 ColorFunction -> "ThermometerColors",
 AxesLabel -> {t, x}, PlotRange -> All]