Hello Pie!
This is called winds alloft, high altitude winds which cut or add flight time to your flight, a head wind slows down your flight time and makes you use up more fuel, whilst a tail wind speeds up your flight time and helps conserve fuel.
Windy.com is good for this, I reccomend using windy for planning.
Also Reccomend looking at this Tutorial by our dear freind Mr Sandstorm, it shows you how to do a flight plan and plan accordingly with winds and how to use fuel.
I hope this helps you.
Warm regards,
Chief305.