Super common problem. You can weld it....but it will eventually crack again. It's better to replace it with the upgraded design (all over Ebay, etc.....it has expansion/accordian joints). But if you can reach the crack with your welder, it's a cheap temp fix.
'98 Jeep TJ Sahara, 31s, 2" lift, SRC front/rear bumpers with carrier, KC Daylighters and driving lights