Two high speed winds traveling in opposite directions in the E layer of the atmosphere create a wind shear. This makes it possible to redistribute and compress ionized particles into clouds without the need to produce more ionization. These ionized clouds may only last a few hours and usually travel from southeast to northwest. They vary in density, which effect at what frequency radio waves will be reflected. The denser the sporadic E cloud, the higher the usable frequency.
The ions are thought to come from vaporization of meteors as they pass through the E-Region and mostly metal ions, iron and magnesium. Because of that, sporadic E is very good at reflecting radio waves so you don't need an elaborate antenna system. All you need is a transceiver, a modest antenna, and good listening skills. The 6 meter band will start hopping in the CW and SSB band portions, but you also find FM activity around 52.525. Because VHF and sporadic E conditions may degenerate quickly, get the basic exchanges done soon (your QTH,Grid Square and Name).
Look for this phenomenon know as sporadic-E during May, June and July. There is a lesser season in the winter months. In the southern temperate zone, like Australia and New Zealand, sporadic-E is highest during their summer season of November, December and January. With a lesser season May to June.
Spordic-E can yield contacts over 1000 miles away with power output as low as 10 watts. This is a phenomenon to watch for and participate in.
Fun Fun Fun!