Can I raise my long run mileage suddenly while still keeping my same average weekly mileage safety? ie: I currently run about 20ish miles a week with my long run being 7 miles. Is upping the ling run from 7 miles to 10 miles too drastic?
I am starting a training plan that stars out at 21mpw with a 10 mile long run, and then peaking at 31mpw with a 13 mile long run. The longest run I have run since December is 7 miles and I am training for a half marathon in April.
With so few other base or foundation miles, moving from 7 to 10 miles for the longest weekly run is possible, however, it will most likely raise your exposure to injury.
FWIW, I'm a trail runner, and back in 2009 while I was finally working my way back into running following a six year layoff, I took a wrong turn and got lost. Prior to that day my longest run in years had been like 6 miles (however, I did have a few 8 miles days split into two runs), on that particular day I ended up going 12 miles and oh geez was I beat when I finished, I mean, you could'a stuck a fork in me and called me done! I had to take three, maybe even four days after that run to rest up, my muscles and joints were that tender.
Well, yeah, there is some increased risk in going straight from 7 to 10. You would have to be careful and "listen to your body" on that run. An alternative would be to do your first 10-miler run/walk, maybe run 5 minutes, walk 1 or 2 minutes (repeat as necessary ). Really, though, what's your hurry? You're peaking at 13 and you have 7 or 8 weeks to get there. You could add one mile per week and still get there easily. Training plans are just plans - they're not law. You may not be used to doing so, but there is nothing wrong with making adjustments in the plan to suit your circumstances.