Runner looking to train for PR over winter

M17, 5'10" 155 lbs. I'm a distance runner, and I'm looking to PR on my half marathon time with a sub-90 minute race in the spring. To do this, I need to shave 4 minutes off my previous record. However, I live in Canada, so my outdoor running has been pretty limited thanks to the snow and cold. I don't really expect to be able to log any serious mileage outside until mid-March, so I was wondering what sort or strength training I could do in the meantime to help build speed and endurance. For about 4 weeks now, I've been mainly focusing on heavy lifts with simpler exercises (Deadlifts, squats, bench, OHP), with some plyometrics thrown in. I've also been running outside when the weather permits, though not the same distances I did in the summer and fall.

Any advice is appreciated!

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