Sandstorm rules from Sandstorm (3.5), ported to 5e

[Jurai]

Sandstorm: Sandstorms arise in waste areas when the wind speed rises above 50 miles per hour (Sandstorm conditions can also occur during a tornado in a waste setting). Sandstorms reduce visibility, smother unprotected flames, and choke protected flames (100% chance). Moreover, sandstorms deal 1d4 points of piercing damage each round to anyone caught out in the open without shelter, but a DC 15 Constitution save halves the damage. A sandstorm leaves 3d8 feet of sand in its wake. All creatures within a sandstorm have disadvantage on all Perception checks based on sight, and are considered to have three-quarters cover and all ranged attacks are made with Disadvantage.

Black Sandstorms deal Necrotic damage instead of Piercing damage, and require a DC 18 Constitution save.

I decided to take the Sandstorm rules from 3.5 and port them up to 5e. Are these rules fair for a party of third level characters? I've run some math (read: two seconds of math), and found that there is a results average of 27, and that the highest an average PC can get without magic items, Barbarian, Expertise, or True Polymorph is 31 on a check. Am I correct and are these saves fair?

[HoarsHalberd]

Sandstorm: Sandstorms arise in waste areas when the wind speed rises above 50 miles per hour (Sandstorm conditions can also occur during a tornado in a waste setting). Sandstorms reduce visibility, smother unprotected flames, and choke protected flames (100% chance). Moreover, sandstorms deal 1d4 points of piercing damage each round to anyone caught out in the open without shelter, but a DC 15 Constitution save halves the damage. A sandstorm leaves 3d8 feet of sand in its wake. All creatures within a sandstorm have disadvantage on all Perception checks based on sight, and are considered to have three-quarters cover and all ranged attacks are made with Disadvantage.

Black Sandstorms deal Necrotic damage instead of Piercing damage, and require a DC 18 Constitution save.

I decided to take the Sandstorm rules from 3.5 and port them up to 5e. Are these rules fair for a party of third level characters? I've run some math (read: two seconds of math), and found that there is a results average of 27, and that the highest an average PC can get without magic items, Barbarian, Expertise, or True Polymorph is 31 on a check. Am I correct and are these saves fair?

If the characters have shelter on them to set up it might be alright. Otherwise they will almost certainly wipe. 3rd level means that a rogue with +2 con would have an average of 19.5 hit points. If it takes them a minute to set up or move to cover and the rogue has a 40% (DC 15 with a +2 mod) chance of succeeding on the con check he will take an average of 6(2.5) +4(2.5/2) damage. Or 20 damage on average. Enough to kill him on average.

All they'll need is a few minutes warning in order to get to cover and plenty of cover and they'll be fine. If they're caught in it, they suffer some deaths.

[b4ndito]

The DCs seem high. What level is your party?

EDIT: Oh, 3rd level. Yeah I'd lower the DC to 12 and 15 respectfully.

[Jurai]

Hmm... Give warning, huh? I can do that, and lower the DCs? Okay, one for lowering so far.

[D-naras]

To put matters in perspective, the maximum DC caused by a spell when using point buy is 13 at levels 1 -3, 14 at level 4, 15 at levels 5-7, 16 at level 8, 17 at level 9-12, 18 at levels 13-16 and 19 at levels 17+. Given that, I would have a normal sandstorm have a DC of 10 and a black sandstorm have a DC of 15. DC 10 makes a sandstorm survivable by those prepared, while DC 15 makes black sandstorm ridiculously lethal to anyone not proficient in Con saves.

[Jurai]

I don't want this to be RIDICULOUSLY lethal. I might make the damage check once per storm until later in the campaign where I'm using this.

[HoarsHalberd]

I don't want this to be RIDICULOUSLY lethal. I might make the damage check once per storm until later in the campaign where I'm using this.

In which case change the storm from once per turn (6 seconds) to once every 20-30 seconds.

[Jurai]

How about once every 1d6 turns? That rounds up to about four turns between checks on average, with some variance due to Mother Nature being fickle.