(if you start crouched (harder to hit)) Aim just under where the lower line connects to the edge of the window frame.
(if you start standing (easier to hit)) Aim for the dot that is chipped paint that is left of the big section of chipped paint thats above the window and crouch)

Nade Time till goes off : 6-7 seconds
Smoke fade: 24 seconds after throw

Nade Ranking (stars are rated as 5 is the worst and 0 is the best, so the more stars the more challenge/time/difficulty/risk)

Setup Time: ★★★☆☆ (approx. 6-7 seconds)
Practice till Flawless execute: ★★★★☆ (approx. 15-20 attempts till you can hit it semi-regularly)
Cost of Failure: ★★★★☆ (Smokes out Underpass)
Throw Difficulty: ★★★☆☆ (Challenging with practice can be easier) (using an AWP ★★☆☆☆)

Nade Overall Rating: ★Advanced★
|| Advanced- A regular nade user in game and practices occasionally ||