Schnauzers afraid of thunderstorms or the sounds of lightning can display all sorts of unsettling behaviors, depending on how severe their fears are.
Here are just some of the signs you may notice from your Miniature Schnauzer if he's frightened from heavy storms.
First of all, consult with your veterinarian. Your vet can prescribe some calming medications for your Mini Schnauzer. In the meantime, you can try some of these at-home remedies to help with your Schnauzer's stress and fear during the loud noises and roars of lightning and thunderstorms.

Spirit Essences Stress Stopper for PetsHelps pets adapt and cope with abnormally stressful situations, such as car rides, thunderstorms & boarding. Also helps pets feel grounded and protected. |  Relieve De Stress Herbal RemedyFor a drama-free day and for stress and anxiety provoking activities like traveling, separation, thunderstorms, grooming, vet visits, moving & more. |  HomeoPet Anxiety TFLN for Dogs and CatsA homeopathic remedy for relief from fear of thunderstorms, fireworks, & other loud noises. Helps to relieve restlessness, anxiety and unwanted stress-related behaviors. |
 HomeoPet Storm Stress 20 to 80 lbs. for cats and dogsA safe and effective homeopathic remedy that promotes calm in pets exhibiting fear from thunderstorms, fireworks, loud noises, hurricanes. |  NaturVet Quiet Moments Calming Aid Soft Chews 5.3oz (65 Chews) for Canines and FelinesHelps support the nervous system in reducing stress and tension. | 
PetAlive PetCalm for Anxiety and Stress in PetsSoothes nervousness in pets. Calms easily startled pets during difficult times and promotes emotional balance and confidence in highly strung pets. |