Storms

Thunderstorms

Towering clouds that produce thunder and lightning and contain strong down drafts

• strong ones may contain hail, winds, and tornadoes 

• mostly occur over tropics

Thunderstorm development

1. Moist air present

2. lifting mechanism

3. atmospheric instability

frequent during warm seasons

movement along front 

• type of lifting mechanism

• cold air forces warm air up 

gust forms 

• type of lifitng mechanism 

• downdrafts act like small cold front

less distinct boundaries

• type of lifting mechanism 

• cool air moves below less buoyant warm air 

high relief (geographic lift)

• type of lifting mechanism 

• mountains force iar upslope 

convergence 

• type of lifting mechanism

• Colliding air causes lifting

atmospheric instability

when the atmosphere promotes vertical air movement; air is moving up and down

Cold front

leading edge of cold air mass that causes warm air to rise

Saturated air

air with the maximum amount of water vapor that it can hold for its temperature/environment

• form clouds as they rise and cool

unsaturated air

not holding the max amount of water vapor for it’s temp/pressure

Adiabatic Lapse Rate 

air expands as they rise

environmental lapse rate

the rate at which the temperature drops as altitude increases (4-9 C/km)

dry abietic lapse rate

rate that unsaturated air cools as it rises; 10C/km

• if DAR> environmental lapse rate, air will stop rising

Moist Abietic Lapse Rate

rate at which saturated air cools as it rises (lower rate than DAR and environmental rate) 

Conditional instability

when an air parcel ruises and becomes saturated, leads to things like clouds and thunderstorms rises

Ordinary thunderstorms

do not have axis or strong winds

stages of ordinary thunderstorm

1. moist air is lifted and expands, forming unstable conditions 

2. ice particles fall and melt into raindrops

3. falling ice particles cause downdraft from cooling 

4. downdraft suppressed updraft, cutting of “energy” and ceasing storm 

squall line tornados

thunderstorms that are organized in a line as a result of a shelf cold front

frontal squall line tornados

storms occur in a very long line which can span states

derechos

“direct”, severe straight winds over large regions

supercell storms

large thunderstorms with long last, rotating upward draft, common tornado precursor

supercell tonado fomation 

1. wind shear produces rolling wind tube near the ground 

2. updraft lifts tube to create a domed cloud 

3. downdraft splits the sotrm into 2 storms

4. wind feeds SSE storm, NW storm dies 

Lighting

charge separation that develops in thunderclouds and causes electrons to jump from small ice crystals (+) to larger ice particles (-)larger

lighting process

1. Updrafts carry crystals to high altitude

2. large particles sit on cloud bottom

3. air act as insulator, electrostatic discharge occurs (lighting)

stepped leader

part of cloud to ground lightning, electrons in cloud surge to ground in steps

positve streamer

ionized electrons from ground rise to meet the stepped leader

electron flow channel

forms when stepped ladder and positive streamer meet, “return stroke” (lightning) occurs 

Thunder

lightning strike massively heats air, and suddne contraction of air following strike causes thunder sudden

downbursts 

strong downward air columns that descend from thunderstorms

microburst

downburst that affects a small area

Hailstones

spherical ice lumps that are supercooled water droplets

hail swatch

path where hail falls to ground