Building a thirteen-week cash flow forecast that people trust

Our monthly profit looked healthy last year, yet we nearly missed payroll twice because large customers paid late. Our accountant now recommends a rolling thirteen-week cash forecast updated every Friday, owned by finance but fed by sales and purchasing.

The first versions were wildly inaccurate because sales entered optimistic collection dates. We started comparing forecast with actual receipts each week and showing the variance openly, which improved discipline quickly. What level of detail do you keep in your short-term cash forecast, and who is accountable for each line?