tikz-cd drawing arrow to another arrow

Question

I am trying to reproduce this image http://www.ats.ucla.edu/stat/stata/faq/model5s.png from this page http://www.ats.ucla.edu/stat/stata/faq/modmed.htm using tikz-cd. I have the following code and diagram. How do I add an arrow from W to the arrow of X to M or to the arrow from M to Y?

I am not sure if it is possible since the arrows themselves are not nodes. Also, is it possible to include an oval or rectangular border around a node? I may not be using the right package. I appreciate any suggestions.

\documentclass{article}
\usepackage{tikz-cd}
\begin{document}

\begin{tikzcd}
    & W \\
    & M \arrow{dr} \\
    X \arrow{ur} \arrow{rr} & & Y
\end{tikzcd}

\end{document}

Thanks, ksint

Answer 1

One possibility using the name key and then using those names to draw the arrows:

The code:

\documentclass{article}
\usepackage{tikz-cd}

\begin{document}

\begin{tikzcd}
& A 
\\
B\arrow[r,""{name=B}] & C\arrow[r,""{name=C}] & D 
\arrow[from=1-2,to=B]\arrow[from=1-2,to=C]
\end{tikzcd}

\begin{tikzcd}
    & W \\
    & M \arrow[dr,""{name=R}] \\
    X \arrow[ur,""{name=L}] \arrow{rr} & & Y
\arrow[from=1-2,to=L]\arrow[from=1-2,to=R]
\end{tikzcd}

\end{document}

Answer 2

Try this:

\documentclass[10pt,a4paper]{article}
\usepackage{tikz-cd}
\begin{document}
    \begin{tikzcd}
        &  W  \\
        & M \arrow{dr} \\
        X \arrow[ur, ""{name=Z}]{} \arrow{rr} & & Y
        \arrow[from=1-2, to=Z, bend right]
    \end{tikzcd}
\end{document}

Output:

Answer 3

Without tikz-cd

\documentclass[tikz,border=2mm]{standalone}
\usetikzlibrary{positioning}

\begin{document}
\begin{tikzpicture}[node distance=1cm,>=latex]
\node[draw] (X) {X};
\node[draw, right=of X] (M) {M};
\node[draw, right=of M] (Y) {Y};
\node[draw, above=of M, fill=yellow!30] (W) {W};
\draw[->] (X)--(M) coordinate[midway] (aux){};
\draw[->] (M)--(Y) coordinate[midway] (aux2){};
\draw[->] (W)--(aux);
\draw[->] (W)--(aux2);
\end{tikzpicture}
\end{document}