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I just want to clear something up here about the whole concept of seeing.
Actually the 300mb is not the only indicator of good seeing on any given night. In fact the absence of the jet stream from your skies almost never assures good seeing. Good seeing comes when all layers of the atmosphere are either still or travelling in the same direction.
Additionally the better chart to use during summer is the 200mb chart. during winter use the 300mb.
However even with or without the jet stream being present seeing can either be good or bad no matter what. The Jet only really affects the fine detail in an image ie tiny craters on the moon and tiny detail on the planets.
Where seeing is formed is the lower and middle layers of the atmosphere. You have to look at the what the middle level is doing more often than not. The middle layer can be going in the same direction as the Jet and you can still get good seeing even with the Jet stream present. However, if these are going in differing directions you can get what is known as fast seeing. That being the target looks really solid but cannot be focused correctly.
When you have local winds and high speed middle level this will also combine to make for very bad seeing. When seeing looks like the stars are smashed and wobbling, this is a result of all three levels travelling in totally different angles and directs.
The bottom line is that predicting seeing is a complicated affair and much attention needs to be paid to all the charts and satellite images. When the Jet is not there, check everything else.
Good luck next time.
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