What to wear cycling
It seems like it should be easy to know what to wear, but it's not as temperature can change throughout a bike ride and there's a bunch of different combinations of gear to use.
If you'd like a tool that recommends gear based on the weather in a location I'd recommend www.dresssmybike.com (which I made).
If you'd prefer to read about what to wear that works too. I've included outfits for different temperature conditions below.
70 Degrees (21 C):
Shorts and a short-sleeve jersey.

60 Degrees (15.5C):
Shorts and long-sleeve jersey or long-sleeve thin undershirt.

50 Degrees (10C):
Tights or leg warmers; heavy long-sleeve jersey with sleeveless or short-sleeve wicking undershirt; or lightweight long-sleeve jersey with long-sleeve undershirt.

45 Degrees (7C):
Tights or leg warmers; long-sleeve wicking undershirt and lined cycling jacket; thin full-fingered gloves; headband covering ears; wool socks and shoe covers.

40 Degrees (4.4C):
Tights or leg warmers; long-sleeve heavy mock turtleneck (I like Under Armour) and lined cycling jacket; medium-weight gloves; headband covering ears; winter cycling shoes, shoe covers, wool socks.

35 Degrees (1.7C):
Heavyweight tights; long-sleeve heavy wicking turtleneck undershirt and heavy cycling jacket; heavy-weight gloves; headband covering ears; winter cycling shoes, shoe covers, wool socks with charcoal toe warmers.

Again I'd recommend using www.dresssmybike.com instead of checking this every time, but that's up to you :)