Lightning mostly is attracted to things such as metal antennas that are high up in the air or any other metal objects that are large and are really close to where the lightning is.
Lightning rarely is attracted to umbrellas unless the umbrellas happens to be in a really close range to the lightning.
The lighting would have to strike within 3 feet of the umbrella before it would be attracted to the umbrella.
To prevent lightning from being attracted to the antenna you should always ground the antenna which will prevent electronics from being damaged that are attached to the antenna.