Checking for a week number in a workflow expression

[Guido1982]

I have the following setup:

• SalesOrders have two fields:
  • A dropdown with numbers 1 through 52 for the week no's.
  • A dropdown with the coming 10 years (so 2018, 2019 and so on).
    

Now I'd like to setup a workflow that runs once a week. The purpose of this workflow is to:

• First check if the selected year is equal to the current one.
• Then check if the week no. is lower then the current week no.
  

If those conditions are met, an e-mail should be sent out. Can I do this through the workflow expression engine and if so, does anyone have some pointers on the syntax?