How do pilots avoid thunderstorms at night over the pacific en route to Australia where there is no radar? And what if a large front develops?
You get by on your airborne weather radar which is good out to about 80 miles.  You may also get help from other pilots ahead of you on your route providing PIREPS to ATC on HF, or talking to you directly if you are close enough to use VHF between each other.  But as far as picking your way around cells, besides being able to see them if you are in the clear, your own weather radar is all there is.

The main limitation of airborne WR is shadowing due to signal attenuation in rain, where the really nasty stuff is hidden (looks black as if the sky was empty) behind less nasty stuff.  Even with the modern radar there is a bit of skill and experience required to interpret the returns and not get fooled by shadows.