Weather and Climate

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Weather and Climate

Notes

• New surface analyses are due TODAY

before lecture begins!

• Reading: these notes


First attempt at analysis . . .


Weather and Climate

(Lecture 27)

Instructor: Prof. Michael C. Morgan

Teaching Assistant: Dianna N. Nelson


Questions from last lecture


Weather near a rapidly moving cold

front typically consists of:

A. light, steady precipitation

B. calm winds and sunny skies

C. cold temperatures and dry

conditions

D. intense precipitation from deep

convection


For a single cell thunderstorm, the stage that

consists of a strong updraft and downdraft

with precipitation is known as:

A. the cumulus stage

B. the mature stage

C. the convective stage

D. the dissipating stage


Besides a lifting mechanism, which of the

following conditions are most favorable to the

development of a thunderstorm

A. cold, moist air at low levels; warm,

moist air aloft

B. warm, moist air at low levels; cold, dry

air aloft

C. cold, dry air at low levels; warm, moist

air aloft

D. d. warm, dry air at low levels, cold,

moist air aloft


Map discussion

http://weatherbonk.com

http://aurora.aos.wisc.edu/~morgan/personal_links.html

http://weather.cod.edu/analysis/analysis.raob.html


Fronts


Formation - Ingredients

• Moisture (water vapor) in the lowest levels

of the atmosphere

• Cold, dry air aloft (2-3 miles above the

surface)

• Lifting mechanism


Air Mass (Single-Cell)

Thunderstorms

• Formed by uneven heating of the earth’s

surface

• Brief, but well-defined lifespan with three

stages

– Cumulus Stage

– Mature Stage

– Dissipating Stage


Three stages


Mature Thunderstorms

• The updraft can become so strong that it

penetrates into a region of stable air,

resulting in a overshooting top.


Which is mature and which is

dissipating


Lifespan of a Thunderstorm

• A single cell, consisting of an updraft and

downdraft, lasts 20 minutes.

• But we have all observed thunderstorms

that appear to last longer than 20

minutes….

WHY


Multicell storms

• Sometimes when the cold downdraft reaches

the surface, it may force the warm, moist

surface air upward

• This rising air can condense and build a new

thunderstorm

Multicell cluster

Multicell line (Squall Line)


Downdrafts


Gust fronts


Gust front


Downbursts


Straight-line winds

• Associated with a cluster of severe

thunderstorms

• May exceed 90 knots

• If wind damage extends 250 miles

along storm path, it is called a

derecho.


Tree damage

What does it look like from a

downburst vs. a derecho


What makes a thunderstorm a

severe thunderstorm


Severe thunderstorm

• Hail ¾” or greater

• Winds in excess of 50 knots (57.5 mph)

•Tornado


Severe thunderstorms


Supercell thunderstorms


Capping inversion

• An important component of creating a

severe thunderstorm is the strength of

the boundary layer cap.

– Too strong nothing develops

– Too weak numerous cumulus clouds

– Just righthelps to funnel the air into a

strong updraft


Supercell thunderstorms

Radar

Weather and Climate


Squall line


Squall line


Tornadoes


Tornadoes


Tornado alley


Photos courtesy of Ross Lazear


Photos courtesy of Ross Lazear


23 June 2004 Madison tornado

From the National Weather Serveice/NOAA:

...DANE COUNTY...

A TORNADO THAT STARTED ABOUT 835 PM ABOUT 2.5

MILES SOUTHWEST OF MIDDLETON...MOVED EAST

SOUTHEAST THROUGH SOUTHERN MADISON JUST

NORTH OF THE SOUTH BELTLINE...AND ENDED ABOUT

844 PM AT A POINT ABOUT 2.3

MILES SOUTH OF THE CAPITOL SQUARE. ESTIMATED

WINDS ABOUT 110 MPH.

SEVERAL BUILDINGS AND SIGNS SUSTAINED DAMAGE

AND NUMEROUS TREES WERE

EITHER UPROOTED OR DAMAGED. PATH LENGTH 7.8

MILES. RATED F1.


23 June 2004 tornado track


Hurricanes (Tropical Cyclones)

• Sustained wind speeds in excess of 74mph

• Tropical origin

• The clear area in the center is called the

eye of the hurricane.


Hurricanes

Eyewall


Hurricanes

• The hurricane season runs from June to

November. (surface water is warm >79 o F)

• Most Atlantic hurricanes form due to a

wave coming off of Africa.

• Hurricanes are very efficient storm

systems


Hurricane stages of development


Hurricane movement

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