I could see this being a white hat op. Solstice is close so lots of daylight. Temperate weather but not super hot yet. If the power goes out, nobody's going to freeze to death and most of the country can survive the outside temps, though some may be a bit uncomfortable. Minimal heat related deaths. Minimal weather-related disruption to transportation if relief supplies needed. Some crops are harvestable now so food less of an issue than other times of year. Kiddos out of school.

If you're going to push an op and want to limit civilian casualties, this is the time of year to do it.