I think you can file a NOTAM for a weather balloon even if you don't need clearance. Might depend on the size and payload, though, like if it's closer to a party balloon than a real weather balloon, and how high it's going.

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firesteelrain 21 hours ago | parent [-]

14 CFR Part 101, Subpart D – Unmanned Free Balloons excludes PicoBalloons due to their size and form

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dylan604 20 hours ago | parent [-]

That would explain the difference in experiences. My balloon was 8' diameter at launch and expanded to ~40' when it burst at ~90k'. Mine needed the radar reflector and blinky lights. They were supposed to blink at a certain rate, but we cheated and had lights blinking faster as that's all we could find for our budget/schedule.

	▲	firesteelrain 19 hours ago \| parent [-]
		I would love to launch a HAB. I learned how to do PicoBalloons from a local group.