Flamethrower

You thrust your hand forward in any direction with an open palm. A line of flame erupts from just in front of your hand, quickly billowing outward. Each creature in a 5 by 15-foot line must make a Dexterity saving throw. A creature takes 4d8 fire damage on a failed save, or half damage on a successful one. 

As a bonus action, you can redirect the line in any direction on a 90-degree angle centered on yourself. The area in between the starting direction and the redirected area are also affected. If, during other creatures' turns over the course of the round, or in redirecting the spell's line, new creatures enter the spell's effect, these creatures must make a Dexterity saving throw as well, to determine damage. 

If you have an ability or feat which allows you to cast a spell as an attack of opportunity, such as War Caster, you may use your reaction -- instead of your bonus action -- to redirect the spell's area of effect. By the start of your next turn, the spell's area of effect may only be redirected once. 

The fire ignites any flammable objects in the area that aren't being worn or carried.

At Higher Levels. When you cast this spell using a spell slot of 5th level or higher, the damage increases by 1d8 for each slot level above 4th, or its distance is increased by 5 feet for every level above 4th.