What caused the March 2, 2012 Tornado Outbreak?

An unseasonably warm air mass moved into the area at the start of the day on March 2. A low tracking from the plains moved almost directly over the Attica area to the north east. Before the low even got here, a cluster of storms from the previous night formed and moved across Illinois and Indiana. These storms produced hail up to golf ball size in Terre Haute Indiana with larger hail further to the west. This hail event was caused by a few lone super cells that tracked for approximately 6 hours!!

A line of storms developed in Illinois and raced east-northeast ward. Shortly thereafter, a PDS tornado watch was issued from our area. (Image Credit: Storm Prediction Center spc.noaa.gov )

As these storms raced east-northeast ward, they encountered a very strong jet stream. The jet stream combined with warm air from the south and cold air crashing in from the north east, produced an immense amount of rotation in the lower levels. Especially in Southern Indiana and Northern Kentucky.

This strong jet also allowed for speeds of the thunderstorms to be extreme. Tornado warning were issued for Central Kentucky that said the speed of the thunderstorm was 85mph. If a tornado is confirmed to move this fast, this would set a new world record which would beat the previous 73mph set by the Tri State Tornado in 1925. (Dr. Jeff Master's Blog ) Tornadoes that move this fast will come and go with little warning. This is also a major factor when it came to the high death toll of the event. On the other hand, there was a lot of warning for this storm system to be very dangerous.

This combination of jet stream, warm air moving north, and cold air rushing in from the northeast caused helicity values to soar over 1000m^2/s^s. High helicity values signify high rotation in various parts of the atmosphere. These 1000+ values were located fairly close to the ground. This is a big reason why tornadoes occurred and were exceptionally strong. (Unfortunately, I can't find a graph for this, you will have to take my word for it. I found this information on the day of the event when I was monitoring it from school/home.)

Another factor, that goes along with the unseasonably warm temperatures, is the high CAPE values. CAPE is instability that feeds thunderstorms. The higher the CAPE the more energy there is in the atmosphere. CAPE in southern Indiana exceeded 1000J/Kg which is more than enough for severe storms to feed off of. High dewpoints (especially in Southern Indiana) also fueled the fire for these storms. Dew points soared into the 60s. Henryville, IN, right before the tornado went through was sitting at 66.7 degrees with a dew point hovering around 60. ( Henryville, IN) Where the line stops is when the tornado struck or about 3:14p.m. You can see where the wind began to pick up and what the pressure was the instant the tornado struck. The pressure was lowered right before the tornado struck. This proves that supercells are miniature low pressure systems themselves.

Here is a radar image of Henryville IN (radar image from wunderground.com) This was a typical radar and wind image seen from Indiana southward to Alabama and Georgia. (Images obtained from Dr. Jeff Master's Blog )

 These radar signatures showed a very strong tornado and the results proved this image. At one point, I was looking at the radar for different areas around the Southern U.S. and I could tell with out showing the warning where tornado warning were at. I saw many hook echos (which is an example of the the image at the top) and many positive wind indicators (immediate top). This outbreak had all the ingredients necessary for a widespread outbreak and it lived up to its potential.

All in all, there have been 915 reports of severe weather thus far. 307 were damaging winds, 464 were hail with 48 being hail larger than 2" in diameter, and an astounding 144 reports of tornadoes. The tornado number means this is how many tornado reports have been received,  not necessarily the number of tornadoes that occurred. At this time 50 tornadoes have been confirmed with 15 EF2s, 10 EF3s, and 1EF4 (Henryville Indiana)