HF (3 to 30 MHz)
VHF (30 to 300 MHz)
UHF (300 to 1,000 MHz)
L band (1,000 to 2,000 MHz)
S band (2 to 4 GHz)
C band (4 to 8 GHz)
X band (8 to 12 GHz)
K band (12 to 40 GHz)
C band weather radar thus has a wavelength of around 3 to 7½ cm, and X-band around 2 to 2½ cm.
I was really only talking about what can be expected from airbourne weather radar, although I expected someone to mention that ocean waves can be shown - interesting if you want to know the swell direction. That is why I only mentioned lakes & rivers above.