Weather Weather

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Weather Weather

SCOTT HANDEL

National Oceanic and Atmospheric Administration

Photo: Courtesy AP

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Outline Outline

• Clouds

• Thunderstorms

• Hail/Lightning

• Tornadoes

• Hurricanes

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CLOUDS

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Cirrus Clouds

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Stratus

Stratus Nimbostratus Nimbostratus

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Cumulus

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Cumulonimbus Cloud

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Cloud Formation

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Thunderstorm Formation

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Lightning

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How Lightning Forms How Lightning Forms

The connection is made and the protons rush up to meet the electrons. It is at that point that we see lightning and hear thunder. A bolt of lightning heats the air along its path causing it to expand rapidly.

Thunder is the sound caused

by rapidly expanding air.

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Hail Hail

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How does Hail Form?

Strong updrafts of warm air and downdrafts of cold air are in a thunderstorm.

If a water droplet is picked up by the

updrafts...it can be carried well above the freezing level. With temperatures below 32°F...our water droplet freezes.

As the frozen droplet begins to

fall...carried by cold downdrafts...it may thaw as it moves into warmer air toward the bottom of the thunderstorm

But...it may also get picked up again by another updraft...carrying it back into very cold air and re-freezing it. With each trip above and below the freezing level our frozen droplet adds another layer of ice.

Finally...our frozen water droplet...with

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What can hail do?

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Tornadoes Tornadoes

What is a tornado?

"a violently rotating column of air, pendant from a cumuliform

cloud or underneath a cumuliform cloud, and often (but not

always) visible as a funnel cloud."

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HOW DO TORNADOES FORM?

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WHERE DO TORNADOES FORM?

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WHY DO TORNADOES LIKE WHY DO TORNADOES LIKE THE CENTRAL U.S.?

THE CENTRAL U.S.?

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Fujita Tornado Damage Scale Fujita Tornado Damage Scale

Scale

Scale Wind Estimate Wind Estimate (MPH)

(MPH) Typical Damage Typical Damage

F0 F0 < 73 < 73

Light – Some damage to chimneys, branches Light – Some damage to chimneys, branches broken, signs damaged.

broken, signs damaged.

F1 F1 73-112 73-112

Moderate – Peels surface off roofs; mobile Moderate – Peels surface off roofs; mobile homes pushed off foundations or overturned.

homes pushed off foundations or overturned.

F2 F2 113-157 113-157

Considerable – Roofs torn off frame houses, Considerable – Roofs torn off frame houses, mobile homes demolished, large trees snapped mobile homes demolished, large trees snapped

F3 F3 158-206 158-206

Severe – Roofs and some walls torn off well Severe – Roofs and some walls torn off well constructed homes, trains overturned

constructed homes, trains overturned

F4 F4 207-260 207-260

Devastating – Well-constructed homes leveled; Devastating – Well-constructed homes leveled;

cars thrown and large missiles generated cars thrown and large missiles generated

F5 F5 261-318 261-318

Incredible – Strong frame houses leveled off Incredible – Strong frame houses leveled off foundation and swept away, trees debarked foundation and swept away, trees debarked

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F0 Damage

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F1 Damage

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F2 Damage

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F3 Damage

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F4 Damage

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F5 Damage

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Tornado Embeds

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Tornado Embeds

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NOAA/Geophysical Fluid Dynamics NOAA/Geophysical Fluid Dynamics Laboratory

Laboratory

timothy.marchok@noaa.gov timothy.marchok@noaa.gov

Princeton University

Quest Science Workshop

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What is a hurricane?

A hurricane is an intense cyclonic storm (i.e., a

cyclone) that begins as an area of low pressure over the tropical oceans.

 “ “ Hurricane” is a specific regional Hurricane” is a specific regional name. In general, these storms are name. In general, these storms are

known as “tropical cyclones”:

– Tropical depression: Tropical depression: winds < 39 mph winds < 39 mph – Tropical storm: Tropical storm: winds < 74 mph winds < 74 mph

– Hurricane: Hurricane: winds winds > > 74 mph 74 mph ( gets named! )

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- - Atlantic and Eastern Pacific Oceans Atlantic and Eastern Pacific Oceans (hurricanes)

(hurricanes)

- Western North Pacific Ocean - Western North Pacific Ocean

(typhoons) (typhoons)

- South Pacific and Indian Oceans - South Pacific and Indian Oceans

(cyclones) (cyclones)

Where do tropical cyclones form?

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(nn) Number of storms per year

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Why are the winds so strong in a Why are the winds so strong in a

hurricane?

force” (PGF). At large distances from a low (e.g., at point A in the diagram on the right), there is almost a balance between the Coriolis effect and the PGF. As a

parcel of air gets closer to the low pressure center, often the pressure gradient intensifies (analogous to a terrain gradient increasing when on a mountainside and getting ready to drop rapidly into a canyon), accelerating

the parcel (this is felt in the increase of winds as you near a hurricane’s center). Close to a strong low, the influence of the Coriolis effect becomes unimportant compared to the PGF, and the parcel moves more in a direction towards the low. Very close to an intense hurricane’s center (e.g., at point B in the diagram on the

right), as the air rotates rapidly around the center, there is nearly a balance between the PGF and an

outward force due to centripetal acceleration.

A B

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How is a lawn mower like a How is a lawn mower like a

hurricane?

Gas provides the fuel for the mower’s engine

The engine uses the fuel to perform work

and move the grass-cutting

blade

The starter rope and spark plug are

the “triggers” for making the mower

start

Exhaust fumes are expelled out

away from the

engine

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The hurricane heat engine: how it The hurricane heat engine: how it

works works

3. Having lost most of its heat and energy, the air is now expelled outward away from the center of the storm in the cooler hurricane outflow at high levels.

In mature hurricanes, an eye forms in the center. Here, the air is

descending and the region is generally cloud-free.

2. The warm, moist air rises in thunderstorms surrounding the eye, supplying the fuel that helps strengthen the storm and intensify the winds.

1. As air rushes into the hurricane’s low pressure center, the air picks up heat and moisture (fuel) from the warm ocean surface.

H L H

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Wind Damage examples Wind Damage examples

A 1x4 board of wood was

pierced

through a palm tree by

Hurricane

Andrew’s winds in August,

1992.

A mobile home park near Miami, FL was completely destroyed by Hurricane Andrew in August, 1992.

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How are hurricanes different from tornadoes?

Hurricanes

Hurricanes Tornadoes Tornadoes

Where they form

Where they form Hurricanes form over warm Hurricanes form over warm water in the tropical oceans water in the tropical oceans and develop best when far and develop best when far

from the jet stream.

Tornadoes form over land Tornadoes form over land and form within storms and form within storms that are often very close that are often very close

to the jet stream to the jet stream

How big they are

How big they are Up to several hundred miles wideUp to several hundred miles wide No more than ¼ mile wideNo more than ¼ mile wide

How long they last

How long they last Average of 9 days (up to 3 Average of 9 days (up to 3 weeks)

weeks) No more than an hourNo more than an hour

How strong the winds How strong the winds

areare

Less than 200 mph

Less than 200 mph Up to 300 mphUp to 300 mph

Occurrences per year

Occurrences per year An average of 10 tropical storms An average of 10 tropical storms in the Atlantic Ocean

in the Atlantic Ocean In the United States, 800-In the United States, 800- 10001000

Advance warning from Advance warning from forecasters

forecasters

Several days

Several days No more than 15-30 minutesNo more than 15-30 minutes

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Saffir Simpson Scale

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Storm Surge

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Storm Surge examples Storm Surge examples

Storm surge from

Hurricane Carol

completely inundates a yacht club in August, 1954.

Hurricane Katrina’s 30-foot storm surge obliterated every home within several blocks of the shoreline in Pass Christian and Waveland, Mississippi.

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