Weather question: barometer

Question

so a barometer reading of less than 29.0 (for the northeast USA) would suggest stormy weather?

Answer 1

It would indicate a nearby low pressure system. If the pressure was continuing to fall, it would indicate an approaching low pressure system. Any time a low pressure system is approaching, the chance for stormy weather is increasing.

So, in essence, your statement is correct.

Answer 2

Not necessarily.  In the desert southwest there is often a thermal low caused by heated air rising and it doesn't indicate rain.  The barometric pressure along with many other atmospheric measurements gives a more accurate prediction of weather than just pressure alone.  29.92 is average sea level pressure.  

Answer 3

Yes, you have it right.  A barometer is based on 36 inches of mercury placed in a tube and placed upside down in an open air dish.  The resulting vacuum settles around 30 in.  Some hurricanes can go as low as 27 in.