Thunderstorms

1
Thunderstorms

• Chapter 14

2
Thunderstorms

• A storm containing lightening and thunder
  convective storms may have heavy rain hail
• Ordinary Cell Thunderstorms
• Air-mass thunderstorms limited wind sheer
• Stages cumulus, mature, dissipating
• Entrainment, downdraft, gust front

3
(No Transcript)
4
A dissipating thunderstorm
5
Thunderstorms

• Multi-cell Thunderstorms
• Thunderstorms that contain a number of convection
  cells, each in a different stage of development,
  moderate to strong wind shear tilt, over
  shooting top

6
Multicell storm
7
Thunderstorms

• Multi-cell Thunderstorms
• Micro-bursts localized downdraft that hits the
  ground and spreads horizontally in a radial burst
  of wind wind shear, virga

8
Dust clouds from microbursts
9
Thunderstorms

• Multi-cell Thunderstorms
• Gust Front leading edge of the cold air
  out-flowing air shelf cloud, roll cloud, outflow
  boundary

10
(No Transcript)
11
Thunderstorms

• Severe thunderstorms one of large hail, wind
  gusts greater than or equal to 50kts, or tornado,
  tilted updraft/downdraft

12
Shelf cloud
13
(No Transcript)
14
Thunderstorms

• Multi-cell Thunderstorms
• Squall-line thunderstorms line of multi-cell
  thunderstorms, pre-frontal squall-line, derecho

15
Pre frontal Squall line
16
(No Transcript)
17
Pre frontal Squall line
18
The thunderstorms are producing strong
straight-line winds called a derecho
19
Thunderstorms

• Multi-cell Thunderstorms
• Meso-scale Convective Complex a number of
  individual multi-cell thunderstorms grow in size
  and organize into a large circular convective
  weather system summer, 10,000km2

20
(No Transcript)
21
Thunderstorms

• Supercell thunderstorms
• Large, long-lasting thunderstorm with a single
  rotating updraft
• Strong vertical wind shear
• Outflow never undercuts updraft
• Classic, high precipitation and low precipitation
  supercells
• Rain free base

22
A supercell thunderstormwith a tornado sweeps
over Texas
23
(No Transcript)
24
(No Transcript)
25
Thunderstorms

• Supercell thunderstorms
• Strong vertical wind shear
• Surface, 850mb, 700mb, 500mb, 300mb conditions
• low-level jet

26
(No Transcript)
27
Thunderstorms

• Supercell thunderstorms
• Cap and convective instability

28
(No Transcript)
29
Thunderstorms

• Thunderstorms and the Dryline
• Sharp, horizontal change in moisture
• Thunderstorms form just east of dryline
• cP, mT, cT

30
Fig. 14-23, p. 384
31
Thunderstorms

• Floods and Flash Floods
• Large floods can be created by training of storm
  systems, Great Flood of 1993
• Flash floods rise rapidly with little or no
  advance warning many times caused by stalled or
  slow moving thunderstorm

32
(No Transcript)
33
downtown Des Moines, Iowa, during July, 1993
Fig. 14-25, p. 387
34
Thunderstorms

• Topic Big Thompson Canyon
• July 31, 1976, 12 inches of rain in 4 hours
  created a flood associated with 35.5million in
  damage and 135 deaths
• Slow moving Thunderstorm

35
Fig. 1, p. 386
36
Flash Floods Slow moving or Stalled thunder
Storm, especially in canyon areas
135 deaths in 1976 flood 12 inches of rain in 4
hours (normal 16 inches /year)
37
(No Transcript)
38
(No Transcript)
39
(No Transcript)
40
Thunderstorms

• Distribution of Thunderstorms
• Most frequent Florida, Gulf Coast, Central Plains
• Fewest Pacific coast and Interior valleys
• Most frequent hail Central Plains

41
(No Transcript)
42
(No Transcript)