This jersey is perfect for temperatures in the the mid 40s-50s with a baselayer. If you're dipping into the low 40s, it still works great, but I've been wearing a vest over it. It's very flattering. I'm 5'-5", 115 lbs with a non-curvy runner's build and got an XS, which fits pretty tight, but doesn't seem to ride up. If you have larger hips, you might want to size up because it's definitely tight at the bottom. My only complaint is that the pockets in the back are really small. I could barely fit my gloves into one pocket.