How to interpret the values of moisture flux convergence?
MFC can be employed to detect frontal structures and possible storms, which can be related with high values of MFC, which means convection of winds with high quantity of moisture...

In a field map, you will be able to identify fronts as structures with high values of MFC. Try to plot along with pressure field for better understanding if you are able to.

Find more info here:
http://www.spc.noaa.gov/publications/banacos/mfc-sls.pdf