You can find out what the jetstream is doing:
Go to
http://www.bom.gov.au/aviation/?ref=ftr
Press "Accept"
On the left hand side, select 'Aviation Observations', this expands to a submenu;
Select 'Aerological Diagrams', and choose a city near or west of your location. West, because at high altitude the prevailing windstream is westerly and ideally you should choose a site upwind of your location.
These are produced by the release of a meteorological balloon carrying a telemetry package and a radar reflector allowing its height and location to be tracked as it rises; from this the BOM calculates the wind speed and direction at altitudes up to the upper atmosphere.
The BOM provides a more detailed explanation of how to read the tick marks (wind speed) and direction.
When the jetstream dies down below 40 km/h the seeing is usually very good, however such nights are rare.
A good clue is a large high pressure system with the centre over your location (learn to read the synoptic maps).
