What is a shortwave?
A shortwave is an area of prolonged low pressures. They are not a low pressure system, but rather low pressure readings.
Can they cause precipitation?
Are they dangerous?
Since shortwaves typically aren't as powerful as a low pressure system, not really.
What does a shortwave look like?
A shortwave can be identified by a series of millibar lines on a map pushed down.
See the lines pushed down in the middle of the country?
That's a shortwave.