Of course, we are hearing only one side of the story, so this advice might not be as accurate as it could be if both sides were known.
This being said, from my lofty 73-year-old perch of wisdom gained through the years, I am reminded of my only daughter's turbulent pubescent years and can recommend several positive changes you can make to improve the situation. First, keep a journal where you can release any pent-up feelings or confusions and then reevaluate them over time to gain perspective. My own daughter had many journals that comforted me after her untimely and wrongful death in 2002. You will find this to be cathartic as you wend your young way through all of the emotions you experience.
Next, look below the surface of your mother's mood swings and verbal assaults to find the real message---the underlying fears and deep-rooted love that is in her heart and mind. There is always love and fear in what a mother does, whether she knows it or not. As you grow older, she might be afraid of "losing you" because you are soon to be on your own...maybe not needing her anymore or, she might fear, losing sight of your love for her. Subconsciously, your mom might be verbally attacking your self-esteem in a misguided effort to keep you dependent upon her, like a firefighter wishing to be seen as courageous who sets the fire that he or she can then be the one to put out.
Whenever my mother would overdo it on criticism or anger, she'd write a long letter and leave it on whichever kid's pillow that she had raged against. You might want to leave such a letter on your mom's pillow or on the kitchen table for her to read after you head for school. If she is feeling powerless as you grow into adulthood and becomes more fearful of being left behind, she might do the types of things you describe in your question, losing sight of how her words and actions effect you, her beloved child. The journal will help you stay in touch with your own turmoil and feelings, so once you get a clear perspective from your writings, put those feelings of anguish in a private letter that your mom can read when she is alone. Reassure her that you do not want to leave her, but that her attack words are hurtful and you wish she would be less critical, more supportive.
Can your mom be distracted during a tirade the way you would a younger sibling? What would happen if during a tirade you simply said, "I love you, Mom...but you are hurting my feelings. Can we just talk?"
And talk to a counselor or someone you trust at school too so that you can unload your pent up fears or feelings. Do things that boost your self-confidence (like acting class or community service). Be patient with yourself and your mom---these hard times will pass.