Before I get to the topic of my blog, I first want to thank mall the good people for their awesome comments. It’s because of you I continue to write, believe me all of you have made a tremendous impact on me. Today I will be writing on Tornadoes. The main topics I will write about are Tornado Ingredients or what is need for their formation, Tornado Genesis, The EF Scale that measures Tornado Intensity, and Tornado Trivia. I am going to get a little technical but stay with me because I will make sense of it all.
1. SUPERCELL AND TORNADO INGREDIENTS FOR FORMATION
There are 4 factors involved in Tornado Development
1. INSTABILITY – All instability means is warm air at the surface where we are and cold air aloft in the atmosphere. So a parcel of air rises when warmed or heated and it will continue to rise if the parcel of air is WARMER than the surrounding air in the environment. This is called Positive Buoyancy. For those who read all my Blogs you know that Latent Heat of Condensation is responsible for the continued rising of air. So once this air is rising it cools condenses and still rises because heat is released through condensation-(when water changes state from a vapor to a liquid. It takes 600 calories a gram, so if you have a lot of vapor you have a lot of calories used, thus a ton of energy absorbed and then released).
B. CAPE – Meteorologists use a CAPE index to measure instability in the atmosphere. CAPE stands for Convective Available Potential Energy, this is a key tool because it tells Meteorologists if there is a chance of thunderstorms, and possibly severe thunderstorms forecasted for a given day. Now the question is How is CAPE measured? CAPE is energy or potential energy, so it is expressed in j/kg, which stands for joules per kilograms. I know it sounds complicated but just remember the higher the joules/kg the greater potential for severe thunderstorms/tornadoes. To obtain CAPE values the National Weather Service gets soundings through release of weather balloons a few times a day that travel 100,000 in the atmosphere. If a local MET says CAPE values are 1000/j/kg, its pretty safe to say its a stable atmosphere, but 3000-4500 j/kg is loaded with energy and we must be alert for severe weather that day. Or at least the potential is there.
Here is an example of incredible instability where that parcel of air is WAY warmer than the Environment Air surrounding it. This is called ELR or Environmental Lapse Rate. The larger temperature contrast between the Parcel air temperature and the Environmental Air temp, the steeper the Lapse Rate, thus more energy is available for severe storms to develop. Diagram provided by www.wx1.eie.edu
2. AMPLE LOW LEVEL MOISTURE –
This is very important for thunderstorm and Tornado development. With abundant low level moisture , this allows water to condense quickly, resulting in a low cloud base. Ample Moisture also allows for updrafts in thunderstorms and tornadoes to continue due to the release of LATENT HEAT OF CONDENSATION. This concept was mentioned above, The moisture at the surface is measured by the DEWPOINT TEMPERATURE. It is what we feel, if the dewpoint temperature is below 60 degrees Fahrenheit it is comfortable seems dry outside and pleasant. For thunderstorms and tornadoes to form and intensify they need dewpoint temps above 60 degrees when it feels like you are wearing the humidity. In Florida and the southeast in the summer Dewpoint are always in the 70+ degree range feeling oppressive. 60 -69 degrees is considered muggy or quite humid and anything over 70 degree dewpoint is considered oppressive. Thunderstorms and Tornadoes thrive on 70+ degree dewpoint.
Graph provided by midwestweather.org. This is a mid-latitude cyclone or a strong Low pressure area probably in spring or early summer. The Low level moisture and instability is located in the Warm Sector of the storm where the warm front passed, and in the wake of the warm front southerly to southwesterly winds have ushered in heat and humidity with high dewpoints to initiate thunderstorm and possibly tornadic development.
3. CAPPING INVERSION –
This is a new development in the research of severe thunderstorms and tornadoes. It is theorized that if a cap is present in the atmosphere it will suppress all little storms to development and focus on a few monster storms. Its akin to pinching or clipping all you’re watermelon flowers to focus on growing that one big melon on the vine. I mentioned inversion and cap I will explain. A CAP INVERSION is when temperature increase with height in a small layer of the atmosphere and air can no longer rise because the environment Air is Warmer than the parcel air causing a sinking of air and stability. Now the Cap in this case is important for SUPERCELLS to form because 1. Its not a strong cap, and 2. the heat and instability building under this Cap can break through it. So, the Inversion Cap is important because it prevents premature release of energy by rising air parcels. And when the CAP is lifted or breached by the Parcels of air it is analogous to removing the lid of a pressure cooker and Rapid uplift of air occurs and explosive development occurs. Supercell Thunderstorms form this way or at least most form this way, and most Severe Tornadoes come from this process.
This is a great diagram from kcstormfront.wordpress.com showing the inversion cap at apprx. 6000 feet. Where the cap layer is relatively small but nonetheless effective in keeping the unstable air below it. Also clouds don’t have that great vertical tower appearance.
4. SHEAR – There are 2 kinds of shear needed for tornado development
A. Directional Shear – This is evident in a change in wind direction at height. For example for tornadoes to form you need to have a southerly flow or SW flow at the surface, as you go up in height the winds will continue to turn in a westerly direction, and as you go above 10,000 feet in a West to Northwest direction.
B. Speed Shear – This shear is similar to directional only difference is that speed shear is wind is increasing with height. For axample at he surface its relatively calm wind but as you go up winds increase dramatically. If you have the support of the Polar Jet, winds can reach 150 mph at 10,000 feet and higher.
The first diagram by typhoonmanila.weebly.com depicts directional shear and the next diagram is the examiner.com illustrates wind shear. With Directional Windshear and vertical Windshear present these two components establish a horizontal motion that can be ingested by the strong updraft and here’s a picture
Chart by geography.hunter.cuny.edu helps me to display the power of directional and speed shear present.
2. TORNADOGENESIS
A. MESOCYCLONE – Most mesocyclones develop in Supercell Thunderstorms. A Mesocyclone is an area of rotation in a Supercell thunderstorm visible on Doppler Radar. If the National Weather Service sees this they will issue a Tornado Warning for an area that has this occurring. Usually if a Mesocyclone is present 20-30 minutes after detection a tornado will form. Not all the time, but a good chance of a tornado forming after a half-hour of mesocyclone detection. A Mesocyclone is tilted and stretched due to the directional and speed shear evident, its diameter decreases and Rotation increases. It analogous to a figure skater pulling her arms closer to her body speeding up her rotation. Finally as speed increases, pressures increase toward the surface.
Great depiction by stormtrack.org showing strong mesocyclone rotation and tornado present and on the ground. Large Hail, damaging winds, and heavy rains are associated with this supercell thunderstorm and Tornado.
2. WALL CLOUD – A Wall Cloud is a precursor to a tornado.
A. As a Mesocyclone develops and intensifies it may produce a Wall Cloud. A Wall Cloud hangs below the rain free base or cloud base. The wall cloud forms from rapid convergence of inflowing air called INFLOW. Or simply put air flowing into the storm. It is really a Progenitor to a Tornado.
3. TORNADO
A. This is where a funnel cloud will originate from the wall cloud. The funnel cloud will connect with the updrafts from the occlusion front(where strong updrafts are present from where the cold front caught up with the warmfront and has lifted it).
B. It becomes a tornado once the connection with the ground is complete. Remember folks it is not a tornado until the condensation funnel has REACHED the ground. The Wall Cloud is often co-located with the occlusion of the rear-flank(back side of storm) and forward flank downdraft(front side).
C. The Forward Flank Downdraft occurs as a result of the heavy rain in the core of the storm, found in the Northeast side. The Rear Flank Downdraft occurs as a result of sinking air on the backside of the storm.
This is a picture of a mature tornado on the ground, you can clearly see the condensation funnel on the ground. It is a large WEDGE tornado meaning the base is really close to the ground. These storms are particularly dangerous because the are hard to see and the winds are ferocious.
4. DISTRIBUTION AND MEASUREMENTS OF TORNADOES
A. Tornadoes are abundantly distributed by the battle of the air masses where cP or continental Polar air mass or cold air mass, meets mT maritime Tropical or warm humid air masses. This occurs in the southeast U.S. and the Southern Plains. In fact cT contintental Tropical air mass a warm and dry air mass meets Maritime tropical air masses warm and humid to form a DRYLINE – This is a moisture gradient front that separates hot and dry and hot and moist air. It is also called a dewpoint front. The dryline is responsible for major tornadoes outbreaks in the central and southern plains, most frequently in Texas and Oklahoma. However tornadoes can happen everywhere, in Florida where I live there are a lot of tornadoes but they are weak because the jet stream and shear are not here. The Midwest and northeast get there tornadoes in the summer. The southeast in the fall and Spring. and the Plains states in Spring and early summer.
B. Enhanced Fujita Scale – The enhanced fujita scale is a modified version of a tornado magnitude scale measuring tornado strength from 0 – 5. 0 beings the weakest and 5 the strongest. The Fujita scale was developed and implemented by Dr. Ted Fujita and Dr. Greg Forbes. The scale goes by EF. I will show a diagram of it.
Thank you wxbrad.com for this graph. You can clearly see the stronger the winds the greater the damage. The only caveat with these scales is the intensity only measures the damage the tornado made and than the NWS gets the data and estimates the wind speed. However, if a EF -5 was in the field and didn’t effect anyone its deemed a minimal tornado because it didn’t do any damage.
5. TORNADO TRIVIA –
- Tornadoes are usually 75meters to 150meters wide.(multiply by 3 to approx. feet).
- The TRI_STATE Tornado a F-5 at the time travelled 350km or 217miles on the ground from Missouri to Indiana killing over 100 people it was the longest tracked tornado.
- Winds can exceed 300mph in the strongest of tornadoes. May 3, 1999 Moore Oklahoma Tornado reached 302mph.
- There are approximately 1000 tornadoes a year in the United States.
- Tornadoes can occur at anytime of year and at any hour of the day.
Well folks that’s it for this time. I hope you enjoyed my blog about tornadoes and until next time be safe when observing weather, especially severe weather. Be well and I will see you all next time. Bye, adios, Au Revoir.