As I write this, the mercury here in New Jersey is inching into the 90s. It seems like just a few weeks ago the trees were still budding. But summer has arrived, and with it, all the new flight planning considerations of the season. Most often, we think of summer as the time for thunderstorms and, maybe, those murky low-visibility days brought on by lingering high pressure, especially here in the Northeast. But the effect of high density altitude on aircraft performance can be sneaky. And if you're not keeping a watchful eye out, it can bite you. Especially flatland pilots venturing into areas of higher elevation on summer vacation trips.