"Somewhat unusual weather patterns", how much can we attribute to jet stream ?

As we experience somewhat unusual weather patterns, how much can we attribute to jet stream changes not previously seen, 

while taking into account both natural and seasonal changes?

During a period with a strong jet stream, weather conditions at the surface tend not to stay in position for long periods of time since the jet stream moves them away quickly.

When the jet stream is weak however, these waves become more amplified (the waves are larger) and move more slowly. Weather patterns at the surface may remain in the same position for longer periods of time and can remain stuck for many days, or even weeks. 

This is particularly significant during more extreme weather events. Long periods of heavy rain lead to flooding, or conversely long term dry conditions lead to drought.

http://www.eyetowardsthesky.com/jet-streams/