What a difference the Sun makes

So the unthinkable happened.  I did a double, 2 2 mile runs oddly enough both were done at the same temp and same humidity(according to weather.com after both runs).  In the morning I was a little sluggish but it seemed really hot/humid.  Tonight when I ran it seemed much cooler.

I was thinking during my run what the best way of going about training.  I was torn between doing a lot of doubles to get my mileage up or just trying to tough out doing some longer runs and trying to make sure I go slow enough to make it home.  Either way I need to make sure I am keeping hydrated all day and potassium intake.  I would really like to make it through the summer running and not have my calf problem come up again.