Spend some time and $$ at the best "lbs" (local bike shop) you can find, have them check your bike to see if it has "BRAKE MODULATORS" installed.
Or you could do a search of the "mechanics" subforum on the subject of poor stopping power/brake modulator.
Brake Modulators are fairly common on bikes at the price point of your Big Box Schwinn/path rider style bike.. They are often the source of poor stopping power in adverse conditions, despite having high performance pads installed.
OH!!, WAIT. I almost forgot. WELCOME TO THE FORUMS!!!