At what time of year is sporadic-E propagation most likely to occur?

Sporadic-E propagation is characterized by unpredictable, dense patches of ionization in the E-layer of the ionosphere. These patches allow for the reflection of higher frequency signals, such as on the 10, 6, and 2-meter bands, over distances of several hundred to a few thousand miles. Statistically, the occurrence of Sporadic-E peaks dramatically during the summer months, centered around the summer solstice. There is also a secondary, much smaller peak around the winter solstice. Unlike normal F-layer propagation, which often sees its best intercontinental DX conditions around the spring and fall equinoxes, Sporadic-E strongly favors the solstices.