What kind of weather conditions are favorable for tornadoes?

Question

What kind of weather conditions are favorable for tornadoes?

Answer 1

Unstable airmasses with a lot of moisture and cold air aloft.   There are conditions as well that cause the rotation but the mean element is instability.   Meaning essentially,  how fast the air is moving upward.

Answer 2

low pressure systems and cold fronts are good triggers. Tornadoes happen most around march and april because you have big temp contrasts. It can be 80 one day and 60 the next.  Once summer gets here, the cold fronts are weaker, doesn't cool the air off as much.  You can also get tornadoes from the hot humid air in the summer, but most tornadoes generally happen about this time of year

Answer 3

Technically, the best setup is an unstable atmosphere where the lower levels are moist and rather warm.  Couple that with a vertical wind structure in the atmosphere that changes in both speed and direction as altitude increases, most likely winds that change in direction from southerly to westerly within about 10 to 15 thousand feet from the surface, as well as an increase in speed.  This setup is known as shear.  Then get things started by initiating the rising air, such as a front or other weak boundary.

Answer 4

they form when a long, funnel-like column of air sinks down from a cumulonimbus cloud, as warm air rises and rotates around it .

Answer 5

Tornadoes can travel at any speeds. The average foreward motion of a tornado is between 25-35 mph, however, speeds can vary from stationary to as much as 65-70 mph! The average direction a tornado travels is from Southwest to Northeast but again tornadoes can travel in any direction.

Tornadoes are most likely to strike areas to the East of the Rocky Mountains and to the West of the Appalachians. However, tornadoes can strike anywhere in the United States and in the world (except Antarctica and North Pole).

For tornadoes to form you need warm moist air at the surface and cold dry air aloft. The warm moist air rides Northward from the Gulf of Mexico and the cool dry air comes in from Canada or from air traveling over the Rocky Mountains. You also need lots of speed shear (change of wind speeds with height) and directional shear (change in wind direction with height). You don't want wind speeds to be too strong though as this can actually kill off tornadoes b/c the updraft gets tilted too much and the storm can't grow very tall. You also need lots of instability but the amount of instability doesn't have to be as great when you are working with lots of shear.

In the Plains you want surface winds to be out of the South or the Southeast. This will bring in the warm moist air needed at the surface. Up at 925mb you want winds to be S or SE as well b/c you need warmth and moisture at this level as well. Dew points here should be above 18-20C. Winds should be between 20-40 knots here. At 850mb winds should be more from the S. This means there is slight directional shear here and there is also moisture at this level. Winds of 30-45 knots is looked for. Dew points here should be greater than 12C-14C. At 700mb you want winds to be more from the WSW. Winds here should be right around 40-45 knots. This would be winds coming more of land than from the Gulf which means the air here would be much drier. Dew points should be less than 5-6C and below 0C is considered significant. You want temps here to be below 8C but this is season dependent. At 500mb you would like to see temperatures below -15C but this again is season dependent. Winds here should be around 60-80 knots. On rare occasions winds at this level could be as much as 100 knots. Meteorologists refer to this as the "barb of death". Winds should be more out of the W here, even NW winds here combined with S or SE winds at the surface indicated strong directional shear. The 500mb winds are also considered the Mid level jet. At 250-300mb, where the upper level jet is located you would like winds to be at least 85-90 mph but no stronger than 135-150 knots. Winds here should be more out of the WNW. You really don't want to see NNW winds as these tend to blow the anvils to areas ahead of the storm which can decrease potential instability. If you look on a map and see a U-shaped bend in the Upper Level Jet these have been noted in some major outbreaks.

You also want high helicity values which you will have if you have strong directional shear.

You should also have very steep lapse rates. Lapse rate is defined as decrease of temperature with height. The steeper the decrease of temperature the steeper the lapse rates. This is also a factor which can strongly increase lift.

The set-ups usually are a low pressure digging in from the Southern Rockies. As the low travels over the Rockies it deepens very quickly. The low then drags a Warm Front Northward which pushes the warm moist air Northward. The low also drags a cold front South and East. This is where the warm moist air and cooler drier air meet. Along warm fronts is usually where the increased tornado threats exist as there is strong directional shear along warm fronts.

Answer 6

Low pressure and cold fronts. A drastic change in temperture is a good warning sign. A good sign a tornado is heading your way is a yellow sky every tornado I have ever been in there was a yellow sky.