1. Supercells
and Tornadoes

2. A SUPERCELL IS AN ENORMOUS THUNDERSTORM CELL WITH ONE UPDRAFT ZONE
The most violent of severe weather storms
(as opposed to MCC and squall lines which have multiple updraft zones)
Supercells have a rotating updraft: MESOCYCLONE
20% of supercells produce tornadoes
Also a Japanese band

3. CONDITIONS PROMOTING SUPERCELL DEVELOPMENT:
mT at surface MEETS…
cP from northwest: cold front
Divergence aloft
East side of trough at 500 mb level
Jet streak in east side of trough
wind shear and low level jet
cT from central Mexico; aloft
(6500 ft; 2 km)
Dryline (dew point front)

5. What causes updraft to rotate?
Vortex tube
Wind shear creates horizontal roll of air (invisible) : VORTEX TUBE

6. UPDRAFT LIFTS TUBE INTO VERTICAL POSITION

7. Mesocyclone Up to 6 mi. diameter; inside supercell
Draws in moist air; energy
Rotation speed increases

8. Mesocyclone
BECOMES VISIBLE AS CONDENSATION TAKES PLACE

11. Video of rotation
Video of tornado, Aurora, NE

12. Wall cloud : BASE OF MESOCYCLONE actually is cool, humid air condensing at a lower height than rest of cloud

18. ANATOMY OF A SUPERCELL:
Forward flank
downdraft
Rear flank downdraft: SW of updraft: produced by cclkwise ppt on outside of
Mesocyclone; chilled air sinks in downdraft ; rain-free base: ppt cannot fall there

19. Overshooting tops

20. SW winds aloft blow ppt to NE; hail N of updraft;; heavy rain N of hail
No ppt inside mesocyclone: bounded weak echo region

21. Regions beneath the supercell receiving precipitation are shown in color: green for light rain, yellow for heavier rain, and red for very heavy rain and hail.

22. Hook echo Conventional radar signature
Precipitation drawn into cyclonic circulation of mesocyclone

23. Velocity signature on radar

24. Velocity signature

26. If rear-flank downdraft interact with surface air , tornado forms:
Cold air of rear-flank and forward flank downdrafts swirls around mesocyclone
Cuts off the warm air from rising
So updraft slows down, shrinks horizontally, stretches vertically
Law of Conservation of Angular Momentum: spins faster!
Tornado vortex

27. The funnel cloud is condensation:
The air is rushing upwards, expanding, cooling, condensing
The funnel cloud looks like it is descending because the air keeps rising and cooling and condensing at lower and lower elevations

32. If funnel cloud contacts
debris cloud on ground….