Will the tempest app work on the first generation IPAD?
The 1st Gen. iPad latest update was iOS 5.1. (source. iPad (1st generation) - Wikipedia
and the Tempest iOS App compatibility is; Compatibility
Requires iOS 9.0 or later. Compatible with iPhone, iPad, and iPod touch. (source. Tempest Weather on the App Store)
So, the short answer is NO.
Looks like the 2nd generation ipad does 9.3.5… so that would be the minimum ipad.