Severe and Unusual Weather Exam 3

Thunderstorms, Hail, Lightning, Tropical Cyclones, Tornadoes

Thunderstorm

Cloud or collection of clouds that produces lightning and thunder

Severe Thunderstorm

Thunderstorm that contains one or more of the following: wind damage or wind gusting to greater than 50 knots (58 mph), hail w/ diameter greater than 1 in, or a tornado

Thunderstorm Ingredients

1. Warm moist air near the surface

2. Lifting mechanism

3. Unstable atmosphere

4. Vertical wind shear

Types of Lifting Mechanisms

1. Differential Surface Heating

2. Topography

3. Fronts

4. Outflow boundaries from other thunderstorms

Lifting Condensation Level (LCL)

the place you switch from using the DALR to using the MALR; there will be a ‘kink’ in the Stuve chart

Level of Free Convection (LFC)

the location in the atmosphere where lifted air becomes warmer than the environment and will rise on its own; its now unstable and doesn’t need a lifting mechanism

Lifted Index

= Temp. of the Environment at 500 mb - Temp of the Parcel at 500 mb

CAPE

proportional to the area of the chart over which the parcel temperature exceeds the environmental temperature (J/kg)

Updraft

Stream of rapidly rising air within a thunderstorm

Anvil

a flat cloud formation at the top of the stream, created when the updraft hits the tropopause and spreads out laterally

Overshooting Top

“Bubble” of cloud that sticks above the anvil; forms when the updraft overshoots the anvil

Mammatus Clouds

‘Pouches’ of clouds that hang down from underneath anvils

Downdraft

Stream of descending air within a thunderstorm

Downburst

downdrafts that are strong enough to cause damage on the ground; downbursts spread out and cause strong straight line winds and damage

Outflow

cold air that develops under a thunderstorm, associated with the downdraft

Gust Front

Boundary between the cool outflow air mass and the warm air mass feeding into the storm

Shelf Cloud

cloud that extends below the base of the storm and forms along gust fronts ("arcus cloud”)

Roll Cloud

cloud that forms along gust front, is tube-like in appearance; detached from the base of the cumulonimbus cloud

Lightning

an electrical discharge or spark in the atmosphere

Charge Distribution in a Cumulonimbus Cloud

when cumulus clouds form we get a separation of charges within the cloud

1. Typical charges near the cloud top

2. A strong area of negative charge in the center of cloud

3. Clouds large negative charge repels negative charge on the ground, leaving positive charge