Question

why is it dangerous to raise an umbrella in a storm

Answer 1

since storm is accompanied with lighting, it is advised not to raise an umbrella as it has metal frame which can easily catch the electric shock.

Answer 2

During  a  lightning  or  thunderstorm,  if  we  carry  an  umbrella,  the  electric  discharge  can  pass  through  the  metallic  stick  of  the  umbrella  and  can  give  a  shock  to  the  person  handling  it.  So,  it  is  advised  not  to  carry  an  umbrella  during  a  thumderstorm  or  lightning.