Platform, device version and operating system:
Windows 10. Steam.
Screenshot or image:
What you were expecting to happen, and what actually happened:
Using the talent Chaos Storm. Noticed something new at the bottom of the screen. Clicked on it to see what it is.
How often does this happen? When did it begin happening?
Rarely.
Steps to make it happen again
It’s a random occurrence while Chaos Storm is active.
Just out of curiosity. Did you see more Mana potion gems during the storm?
No, I did not.
Interesting find, this is not even present on beta translations… I’m gonna do some research 
Hey @rbchaffe
I’ve passed this on to the development team to investigate further.
Thanks for attaching this screenshot as well!
Jeto - Support Human 
Possibly the Uber Doomstorm that is going to be introduced with Archproxy Yvendra?
Uber Doomstorm has been assigned to “STORM9” it would appear, “STORM16” seems to be something new.
"[TROOPHELP_STORM0_1]": "Icestorm",
"[TROOPHELP_STORM0_2]": "Blue Gems fall more than the other colors",
"[TROOPHELP_STORM0_4_1]": "Madness Storm",
"[TROOPHELP_STORM0_4_2]": "Blue and Purple Gems fall more than the other colors",
"[TROOPHELP_STORM1_1]": "Leafstorm",
"[TROOPHELP_STORM1_2]": "Green Gems fall more than the other colors",
"[TROOPHELP_STORM2_1]": "Firestorm",
"[TROOPHELP_STORM2_2]": "Red Gems fall more than the other colors",
"[TROOPHELP_STORM2_3_1]": "Electrostorm",
"[TROOPHELP_STORM2_3_2]": "Red and Yellow Gems fall more than the other colors",
"[TROOPHELP_STORM2_4_1]": "Hellstorm",
"[TROOPHELP_STORM2_4_2]": "Red and Purple Gems fall more than the other colors",
"[TROOPHELP_STORM3_1]": "Lightstorm",
"[TROOPHELP_STORM3_2]": "Yellow Gems fall more than the other colors",
"[TROOPHELP_STORM3_4_1]": "Starstorm",
"[TROOPHELP_STORM3_4_2]": "Yellow and Purple Gems fall more than the other colors",
"[TROOPHELP_STORM4_1]": "Darkstorm",
"[TROOPHELP_STORM4_2]": "Purple Gems fall more than the other colors",
"[TROOPHELP_STORM5_1]": "Duststorm",
"[TROOPHELP_STORM5_2]": "Brown Gems fall more than the other colors",
"[TROOPHELP_STORM6_1]": "Bonestorm",
"[TROOPHELP_STORM6_2]": "Skull Gems fall more than the other colors",
"[TROOPHELP_STORM7_1]": "Doomstorm",
"[TROOPHELP_STORM7_2]": "Doomskulls fall more than the other colors",
"[TROOPHELP_STORM9_1]": "Uber Doomstorm",
"[TROOPHELP_STORM9_2]": "Uber Doomskulls fall more than the other colors",
"[TROOPHELP_STORM10_1]": "Howlstorm",
"[TROOPHELP_STORM10_2]": "Lycanthropy Gems fall more than normal",
Interesting. Going by their naming scheme it’s not a dual storm, rather something unique. Based on the question from @awryan and applying the standard storm sequence past Howlstorm, possibly increased chance for brown potions to drop in?
I can confirm, gem 16 is the brown mana potion.