The supercell storm is the pinnacle of thunderstorm formation. This page includes info on supercell structure, how tornadoes are formed and historical tornado events both past and present. Fellow storm chasers Reed Timmer and Joel Taylor from Oklahoma, USA. chase these regularly. You can visit his site at http://tornadovideos.net
GREENSBURG EF5 DEADLY TORNADO 2007
A fitting music video to the victims of this event.
Footage of the 1999 Oklahoma tornado outbreak. 8 minutes of jaw dropping news footage.
http://video.google.com/videoplay?docid=-2000750381881061105&q=May+3+1999+tornado+coverage&ei=f1gjSK6AEoac4gLnvui1AQ
I strongly recommend reading Prof Howard Bluestein's
book titled 'Tornado Alley. Monster storms of the Great Plains'
avaiable through http://amazon.com/
Oklahoma City holds the the enviable or unenviable record for the most hits by tornadoes. Over 100+ in fact - although this has been updated as season 2007-8 progresses, Huntsville AL comes in second.
Supercells are the ultimate thunderstorm. Not only are they able to sustain their own longevity by utilizing the conditions to their own benefit, but they are also predatory storms which feed off weaker cells nearby, but also storms ahead of them to become stronger!
Okay, time to get into the nitty gritty of supercells and tornadoes. What causes them and what are they. Supercells/storms are categorized into three main types; HP (high precipitation) LP (low precipitation) and Classic.
The obvious answer is always that tornadoes are borne from supercells resulting in... "Cold air moving south from Canada and meeting warm moist air from the Gulf Of Mexico and dry air from the Rockies". This is a gross oversimplification.
Many storms form under these scenarios and almost never come close to producing tornadoes. Storms are found on cold fronts, warm fronts and dry lines anyway. Supercells by their nature are defined as having a persistent rotating updraught, that's the difference. They rotate anticlockwise in the northern hemisphere and clockwise in the southern hemisphere Even more incredible that in reality supercells are rare and tornadoes even rarer - if you can believe that the US has on average 1800 twisters per season!
Outstanding supercell photo courtesy of Kevin Cox/NSSL/NOAA)
LP storms/supercells
(Lakeview TX tornado shot courtesy NSSL)
(global tornado requency)
F1 - 73 - 112 mph / 3 second gust @ 79 - 117.
F2 - 113 - 157 mph / 3 second gust @ 118 - 161.
F3 - 158 - 206 mph / 3 second gust @ 162 - 209.
F4 - 207 - 260 mph / 3 second gust @ 210 -261
F5 - 261 - 318 mph / 3 second gust @ 262 - 317
F6 - greater than 319 mph.
EF 1 - 3 second gust @ 86 - 110
EF 2 - 3 second gust @ 111 - 135
EF 3 - 3 second gust @ 136 - 165
EF 4 - 3 second gust @ 166 - 200
EF 5 - 3 second gust over 200.
(photo NSSL)
Hodographs display different heights in millibars as surface winds up to 700mb are blue, from 700 through to 300mb are yellow and the winds above 300mb are in white. The dots are the actual wind velocities (the direction and speed). The numbers by the dot represent the pressure level at which this velocity was located - ie: 7 = 700mb, 3 = 300mb. Colours may vary but an example of a hodograph is further down .
Generally 'standard storms or pulse storms have an erratic movement on the graph, multicells have a defined gradual increased line to the right with horizontal movement. Supercells have a more horizontal lineage to the right without any erratic behaviour. Whilst all show increased rotation (shear) and a gradual increase in speed, multicells and supercells have significant speed increases along a broad path in their motion.
Diagram of converging cold and warm fronts with low pressure areas - triple point scenario. An occluded front is formed during the process of cyclogenesis when a cold front overtakes a warm front. The cold and warm fronts curve naturally poleward into the point of occlusion, which is also known as the triple point in meteorology. Supercells are often tornadic with these systems.
(below is a past Skew-T shounding from Mississippi in which an F3 tornado grounded)
(Below is a Dopplar radar storm velocity wind image.)
The hodograph shows storm motion from the west at 15kts (remembering that supercells tend to be 'right movers'). The figures in the colum represent direction and wind speed at the different heights.
Courtesy Matthew J Bunkers NWS
As can be seen from just these charts etcetera, there's a hell of a lot of information chasers and meteorologists have to consider! Even when all the atmospheric conditions seem perfect, the CAPE, CIN, shear, WRF models - it can all go to blue sky if something changes. Supercells are no different.
All storms are dependant on the 'right' conditions for the right amount of time. A weakening of shear, a strengthening of upper winds, cold inflow from cold pools - over a period of time what looks like a grandios storm could be a fizzer - but that's what chasing is all about. Education and observation.
(two charts courtesy of NWS/NSSL)
This incredible chart below shows a 100mb pressure drop as it passed over a pressure sensor. This is a fantastic example of the forces around and within a tornado. 100mb drop in less than 2 minutes!
SIGNIFICANT HISTORICAL TORNADO OUTBREAKS:In this section I've put some info on some of the more historical tornado events that have happened over the years. In review also I'll include events from 2007 as these will be remembered as historical with well over 150 tornadoes sighted to date (May 2007) and more no doubt by season's end. Not only were there many killed but whole communities wiped out by killer storms.
Why some seasons are worse than others is probably anyone's guess, whether they occur in seasonal cycles or if it's just plain atmospheric conditions that meet the criteria for severe weather on a sustained scale. One thing is for sure, outbreaks continue to occur when we least expect them. If tornadoes are actually 'rare' with supercell formation then these must surely remind us that significant storm systems can produce killer tornadoes on a wide scale and not are not always localised events on the plains or elswhere.
The Oklahoma City tornadoes of June 13 1998 and October 4 1998.
(photos & graphs courtesy of NOAA/NSSL/NWS Norman)
9 separate tornadoes touched down in central and western Oklahoma on 13 June 1998. Thunderstorms developed during the afternoon and quickly grew to supercell status and tracked eastward into the central sections of the state. One initial storm was so powerful it spawned an amazing 7 individual tornadoes as it tracked through Oklahoma from the Canadian County. Although so many tornadoes were produced only two were rated F2, four rated F0 and three rated F1. Which probably proves that not every 'mother of all supercells' produces just one giant F4-5. Thankfully there were no fatalities during this outbreak although there were many injuries (21) reported in Oklahoma County. Injuries that were sustained were confined to the Frontier City theme park from an F2 tornado when it crossed Interstate 35.
(separate Oklahoma tornado path in 1999)
The tornadoes developed near a dry line and the most significant cell developed at around 4pm CST. The majority of storms spawned tornadoes between 4:45pm to 8:23pm from Blaine County right across to El Reno, in the Canadian County, North Oklahoma City and Northeast OKC. The general wind speeds were from 73 - 157mph within the F0 to F2 range.
(Okalhoma 1999 tornadic supercells)
List of tornadoes which occurred in
central and western Oklahoma on 6/13/1998:
|
1998 Oklahoma tornado outbreak
Map of Tornadoes in the
Immediate Oklahoma City Area:
At least 19 tornadoes struck the portion of Oklahoma served by the NWS Norman office. These include tornadoes in the cities of Moore and Shawnee. Eight more other tornadoes touched down in northeastern Oklahoma in the area served by the NWS office in Tulsa.
| Tornado Timeline on October 4, 1998 | |||||
|---|---|---|---|---|---|
| Tornado ID |
Time | County | Location | Intensity | Length (miles) |
| A1 | 3:25-3:43 | Woods/Alfalfa | 11 SSW Dacoma - 4 NW of Carmen | F2 | ~10 miles |
| A2 | 4:05 | Alfalfa | 5 SE Cherokee | F0 | short |
| A3 | 5:04 | Grant | 5 W Medford | F0 | short |
| B1 | 5:38-5:41 | Blaine | 8 SW - 6 SW Watonga | F0 | 1.5 miles |
| B2 | 5:50-6:12 | Blaine | 3 SW Watonga - 9 ENE Watonga | F2 | 12 miles |
| C1 | 6:14 | Comanche | Just north of Lake Lawtonka (About 5 N Medicine Park) | F0 | short |
| B3 | 6:28-6:42 | Kingfisher | 6 SW Dover - 2 SE Dover | F1 | 7 miles |
| B4 | 6:47-6:56 | Payne/Noble | Lake Carl Blackwell - just east of Lake McMurtry (10 W Stillwater - 6 NW Stillwater) | F1 | 6 miles |
| C2 | 6:45 | Caddo | 1 NE Cyril | F0 | 1/2 mile |
| C3 | 6:54-6:55 | Grady | 9 WSW Ninnekah - 7 WSW Ninnekah | F2 | 2 miles |
| C4 | 8:15-8:21 | Grady/McClain | 4 NW Blanchard - just SW of Newcastle | F2 | 5 miles |
| C5 | 8:26-8:28 | McClain/Cleveland | Extreme north Newcastle into extreme SW OKC | F0 | 1.5 miles |
| C6 | 8:34-8:41 | Cleveland | Moore | F2 | 3 miles |
| C7 | 9:37-9:40 | Lincoln | 4 SE Meeker - 5 E Meeker | F2 | 3 miles |
| C8 | 9:45-9:52 | Lincoln | 7 W Prague - 4 NW Prague | F2 | 6 miles |
| D1 | 9:50-9:55 | Pottawatomie | NW Shawnee | F1 | 3 miles |
| C9 | 9:52-10:08 | Lincoln | 6 NW Prague - 7 NNE Prague | F1 | 8 miles |
| D2 | 9:58-10:00 | Pottawatomie | SE Shawnee | F1 | 2 miles |
| D3 | 10:08-10:25 | Seminole/ Pottawatomie | 5 WNW of Little - Center View - 3 SE Prague | F3 | 10 miles |
The Red River Valley tornado
outbreak of April 10, 1979
(below is track path map made by Dr Fujita/courtesy NSSL - note numbers indicating each tornado's rating)
Below are some images from different areas affected by these storms.
(Storm track of Wichita Falls supercell/vehicles scattered like toys from the Seymour TX tornado April 10 1979 This link will take you to all the tornado images from various people. Worth a view at http://www.srh.noaa.gov/oun/wxevents/19790410/wichitafalls.php
(All photos courtesy NSSL)
(second photo of Vernon '79 tornado courtesy Dennis Lingnau) 
)
The 1925 Tri-state tornado outbreak. In 1925 weather records and observation techniques were obviously not what they are today and given our knowledge of such storms today reminds us this outbreak surely must rate as truly significant.
On March 18 looking at the weather conditions one could assume there was a moderate to severe risk for tornado formation! Here's a brief summation of the weather ingredients courtesy of the NOAA/NWS report;
'During the morning a surface low pressure area over northwest Arkansas and southwest Missouri tracked across southeast Missouri, southern Illinois and southwest Indiana during the day, reaching eastern Indiana that evening. Extending east from the low was a warm front with a cold front trailing to the southwest. as the low tracked northeast during the day its associated warm front advanced north allowing warm moist air from the Gulf of Mexico to infiltrate the Tri-state area. In fact, temperatures that started out in the 50s during the morning reached the 60s over most of the tornado track by 1pm in teh area of Cairo, Illinois by 4pm.
We can assume from that that the lifting mechanism was in place! (tornado track map courtesy John W Wilson, 'Illinois Tornadoes') What can also be inferred also that there must have been very good upper level support given the fact that the tornado traveled at speeds of 60 to 70 mph along most of its path, we can safely assume that perhaps 100 knot upper level jet max was nosing into the area from the west-southwest. With veering winds (south at the surface becoming west-southwest aloft) wind shear was also present to help initiate the storm's rotation. There must have been decent instability as well with warm air advection at the surface and probably cold air advection in the upper levels.
( NOAA/NSSL photo)
The damage and death toll was incredible - hopefully never to be repeated, the facts below are startling!
Photos and report from resident in Jarrell from that destructive tornado that destroyed a community and several lives. http://www.tagworld.com/sklee/World/MyWeb.aspx?page=5dbd8664-b7ae-4c6b-b6e4-00536b1647c0
FACTS: 3 states affected (Missouri, lllinois, Indiana) 13 counties affected. 19+ communities affected. 219 mile path length!!! Accounts of a mile wide path width. 3 hours of continuous devastation. 1:01pm - tornado touched down 3 miles NNW of Ellington, Missouri. 4:30pm tornado dissipated about 3 miles SW of Petersburg, Indiana. 62 mph average speed. 73 mph record speed between Gorham and Murphysboro. F5 tornado with winds perhaps in excess of 300mph. 28.87" lowest pressure measured on a barograph trace the the Old Ben Coal Mine in west Frankfort, Illinios. 695 deaths. 234 deaths in Murphysboro. 33 deaths at the De Soto school (only bombings and gas explosions have taken higher school tolls) 2,027 injured 15,000 homes destroyed.
THE MAY 4 2007 GREENSBURG EF5 TORNADO.
On Friday night at around 7:12pm the town of Greensburg in the Comanche/Kiowa County was obliterated by an EF5, 1.7 mile wide tornado. 17 people lost their lives.
(NASA/GOES satellite photo of storms affecting Greensburg)
WEATHER SUMMARY OF THIS EVENT:
The Storm Prediction Centre issued a moderate risk across parts of Kansas, Oklahoma and Nebraska on May 4 while temps were in the mid to high 80F. A powerful low pressure system developed across the southern Rockies and a warm front provided additonal moisture coming from the Gulf of Mexico and with the increasing amounts of instability across much of the region. A dry line which divides dry and humid air was positioned near the areas affected by the system. This scenerio is a chasers dream, unfortunately it also is ripe for violent supercells, high winds and large hail - and tornadoes.
On May 5 the same centre issued a high risk for Central Kansas and central nebraska wehre additional destructive tornadoes were possible. If that wasn't enough, softball sized hail, high winds and flooding were possible. (estimated wind of 145km/h was reported!) On May 6 the centre issued a moderate risk for severe storms over parts of Central Kansas and northwestern Oklahoma. At least 10 MORE tornadoes were reported that day in the same general area as the preceding two days! A slight risk was issued but no tornadoes were reported on May 7. The days of tornado outbreaks were May 4-6 2007. Total duration was 48 hours. Maximum rated tornado grounded EF5. Total tornadoes sighted - and incredible 72 confirmed, 143 reported. Fatalities 14. Most of the Central United States was affected.
Total destruction of the community and many photos can be seen here from residents and professional chasers http://www.greensburggreentown.org/photos.
Manitoba, Canada F5 tornado June 22
2007.
Weather Conditions Leading Up To The
Tornado
The synoptic situation on June 22 was conducive to a major severe weather event in southern Manitoba. A low pressure system came in from Saskatchewan through the day, and then moved over southern Manitoba throughout the evening. A warm front was positioned north of Elie for much of the day with a trailing cold front residing west of Elie near the Lake Manitoba basin southwest through southeast Saskatchewan. A lake breeze boundary was also present south of Lake Manitoba.
(NSSL photo of a wedge tornado)
Very warm air was situated over Southern Manitoba that day as temperatures climbed into the high 20s°C (low 80s°F). The humidity was also uncomfortably high, with dewpoints ranging from 18-22°C (65-72°F). Directional and speed shear were present as well as high helicity values. These conditions were favourable for supercells which are thunderstorms with rotating updrafts, and they developed within the warm sector located in the Red River Valley and areas farther west. The situation was exacerbated by the presence of the lake breeze boundary because the atmosphere was capped through much of the day with little in the way of a trigger. This boundary provided the focus for storms to develop rapidly and become severe, given the high instability present.
Don't ever believe that strong winds can't kill you. Even a small CAT1 cyclone can whip up winds that can hurl objects around. This record was impaled into a tree during the Tri-State tornado outbreak in the USA. It should serve as a visual warning to stay indoors during severe weather events.
Here's the current average tornado data from the Severe Prediction Centre in the USA for 08. Increased tornado activity is evident.
Below is the 2007-2009 tornado hit list. Just add around 20 more red dots and you still won't keep up as of May 2009!
