The heat wave over the eastern US has introduced higher radiation readings with it. . Again, this has to do with sinking air from upper levels of the atmosphere… but, unlike the recent Indiana radiation event, where the sinking had to do with convergence of two separate air streams in the vicinity of the jet stream, this time the sinking air is from an upper-level ridge which features sinking air (subsidence) from the upper levels, compresses it, and heats it. It is the same principle that your refrigerator uses, the air is compressed, heats up, the heat is pumped out. This time, though, there is no jet stream nearby. Beta radiation on the morning of June 20 was elevated in Pittsburgh PA, which was under the upper ridge. The wind in the early morning was calm which caused the radiation to build up, just like in South Bend. Later, the wind picked up and the radiation level dropped. A similar thing happened in Baltimore and Washington DC.
So there is radiation in the upper air (30,000 feet) far away from the jet stream. It is worse in the jet stream, but there is a substantial amount outside of it, as Potrblog pointed out in his recent rain radiation measurement. We have a radioactive cloud over most or all of the US now.