cloudy black sky,cold temperature dropping and snow or rain falling.
Tornadoes are not a result of oceanic conditions, they are a result of atmosphereic conditions. See the related question for more information.
No, tornadoes never cause a blizzard. I will note that some storm systems that produce blizzard conditions on their northwest side, can also produce tornadoes on their southeast side. Perfect example was March 13, 1993 when a storm storm system moved out of the Gulf of Mexico (While Alabama and Georgia were getting blizzard conditions, Florida was getting tornadoes)
Tornadoes occur in other countries besides the US. However, the US heartland has ideal conditions for tornadoes.
The Tornadoes website offers a variety of information about tornadoes. These include: types and categories of tornadoes, weather conditions that signify tornadoes forming, and safety tips.
Generally not. Tornadoes form from thunderstorms called supercells, which form under similar conditions to ordinary thunderstorms and as anybody can tell you, thunderstorms don't need to form over an ocean. That said, some tornadoes do form on the ocean.
No, not really. The national weather service can see that some conditions exist that could lead to a tornado, but they can not predict when it will happen or where.
if conditions are favorable then yes.
Floods, Tornadoes and wins
If general weather conditions favor the formation of tornadoes then a tornado watch is issued.
There is no way to avoid tornadoes. Weather conditions cause these and unfortunately there is no way to change the weather.
Cold fronts often do result in storms that produce tornadoes, but are not a direct cause of tornadoes. Not all tornadoes are associated with cold fronts, nor do all cold fronts result in the formation of tornadoes. Other conditions, such as wind shear and instability, need to be present for tornadoes to occur. Squall lines can produce tornadoes, but those tornadoes are usually short-lived and weak. Tornadoes are more often associated with discrete supercell thunderstorms.
Not directly. Condensation can trigger thunderstorm. If these thunderstorms are strong enough and encounter the right conditions then they can produce tornadoes.