front-flank downdraft

rear-flank downdraft

front-flank gust front

rear-flank gust front

rotating updraft

upper-levelwinds overhanging

anvil

Supercells: Labelingthe Parts

(as viewed from the SE)

   

- Remember: supercells form in high-shear environments

The Supercell Updraft and Tornadoes

When a tornado forms, it's usually part of the supercell's rotating updraft. So why does the updraft rotate in the first place?

   

The shear in the environmental winds provides a source of background rotation. (Think of rolling a pencil between your two hands....)

   

shear in the environment

The end result is an environment favorable for tornado formation (Roughly 20-25% of supercells produce tornadoes.)

   

a rotating wall cloud at the base of a supercell updraft

   

and another, this time with tornado

   

this one also had a tornado, shortly before the (clearly photoshopped) picture was snapped

   

Favorable supercell conditions (and storm conditions in general) are when warm, humid air off the Gulf is drawn northward below an upper-level disturbance with strong shear, often as part of a developing cyclone.

   

   

Conditions for the April 15, 2011 Tornado Outbreak

   

EF0

EF1

EF2

EF3

EF4

EF5

64-85 mph

86-110 mph

111-135 mph

136-165 mph

166-200 mph

> 200 mph

The Enhanced Fujita (EF) Damage Scale

   

Frequency of tornado occurrence(average number per year by state)

Where are tornadoes most likely?

   Number of tornadoes by month in the US

What time of year are tornadoes most likely?

   Number of tornadoes by time of day in the US

What time of day are tornadoes most likely?

   

● Finally, large collections of individual storms (including any of the three types) often organize themselves into much larger systems, called mesoscale convective systems (MCS)

● The classic MCS types include:

● Squall lines usually form form in environments with significant shear

Collections of Storms

   

Collections of Storms

● MCCs tend to form in environments with weaker shear

● The classic MCS types include:

● Finally, large collections of individual storms (including any of the three types) often organize themselves into much larger systems, called mesoscale convective systems (MCS)