What is the barometric pressure during a tornado?

Question

What is the barometric pressure during a tornado?

Answer 1

There are very very few reliable measurements, but about 10% lower than ambient is a reasonable estimate.

Answer 2

Tim Samaras a storm chaser and tornado researcher designed a probe along with the National Geographic channel. It is dubbed the "turtle" it's almost pyramid shaped, well anyway they put it in the path of a tornado.

There were cameras in every direction to video the tornado. They also had pressure reading sensors, they discovered that the pressure had dropped a hundred millibars at the tornado's center, the biggest drop ever recorded! So yes it drops low very low!