[Majromax]

In that case, the interpolation includes a vertical component as well. You'll see the effects of the lapse rate (change in temperature with height).

That's great for you, but it means that your forecast (of [my elevation, my coordinates]) is not much more accurate than one for ([my elevation, my coordinates plus a few hundred yards]).

More technically: "surface" isn't a smooth variable when elevation changes quickly, but interpolation like that performed by weather.gov necessarily works on smooth fields. Applying post-facto elevation is great and worthwhile, but it doesn't improve the accuracy in a technical sense.