Need A client Expression for the Following logic:

We have to write a client expression with the  following condition ,

(If last update date date < last forecast date then use Base Override LVL1 else Base Override LVL1 – Latest Forecast).

Here Base Override LVL1 is a customized series. and What I want to do is To compare the  Recent Update date with the recent forecast date and use the above logic accordingly.

Can anyone please suggest?