Temiguls Stormlight Web

A web of crackling light manifests above casters head. Threads of azure beams of crackling light streaks toward equal number of creatures within attacking range as anchoring threads for the web. At the same time strong chaotic winds whirls around in attack area. 

Make a ranged spell attack against each target. On a hit targets takes 4d6+2 Lightning damage,  and has to save vs con or be stunned.  Target can try (reaction action or bonus action) to save at end of each of targets turns. There will be at least 4 beams that shoots out and maximum 4 beams + 1 beam per every 2nd spell level above 4th of the casters choosing. (e.g extra beams at 6th and 8th) If at least half the beams hit to web is anchored and the beams stays locked with the targets. Caster can target other things but only attacked living creatures can function as an anchor for the web.

The spell's damage increases by 1d6 per every second spell level above 4th. (extra die at 5th,7th and 9th)  So an upcast 7th lvl spell could be 5 beams that would do 6D6+2 in damage. 

If the web anchors (at least 50% of the targets are hit) it remains.  If the web remain it will remain for spell lvl number of rounds with a  secondary range of 20´+10  per spell lvl. If concentration breaks or less than 50% of original beams is anchored the web disappears. The normal way  to break an anchor is to move out of anchor range.  The beams are flexible and attached so cover won´t break it. Possibly a door without any light allowed through. (No keyholes or the like, e g well made dwarven door or the like). Other ways are antimagic for example.

Each consecutive round the caster can use his action to make a secondary hit and pump out damage to the hit targets. The damage is 1 die less than first hit and 1 less die for each round of attack . Save for half.

In addition the range of the net shrinks with 10´r per secondary hit used. 

During the webs existense the strong winds around caster could cause problems. Normal humans in normal conditions might not have anymore penalties than -2 to hit with range weopons from a range more than 30 feet. towards targets in or on other side of area. Tiny creatures probably have at least difficult terrain. The enviroment might make it more difficult if for example if the area are sand or snow cowered the visibility will be poor and the difficult terrain will be for all creatures not native to those conditions.