Pg. 37

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Wild Weather
Pg. 37 75 of deaths from Natural Disasters are
from weather More than EQ, MW, and volcanoes
combined WHY??? OVERVIEW (we will be adding a
few others but basically) principles of
weather thunderstorms wind tornadoes extre
me heat and drought
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Wild Weather
Pg. 37 PRINCIPLES OF WEATHER Water Heat (sun)
weather Warm air more heat energy and more
moisture Cool Air less heat energy and less
moisture WATER and WATER VAPOR has huge heat
capacity ND pg. 273 table 10.1 Snickers
vs. rice cake absorbs and holds LOTS of heat
transports it around the earth and releases
it HEAT - more of suns energy absorbed at
equator less at poles due to angle earth is
tilted Pole vs. equator sun energy AIR
MOVEMENTwarm air to poles cool air to
equator but things complicate this simplicity
often STORMS
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Wild Weather
Pg. 37 WHAT CAUSES WEATHER IN THE UNITED
STATES?? 1.) Global Wind Patterns Air heated at
equator heats, expands and rises. As expands
(lowers pressure/density) causes
cooling (adiabatic process) total heat stays the
same but volume increase causes temperature to
drop Cooling air sinks and compresses becoming
dense so warms heat at surface warms
also. GLOBAL WIND PATTERNS
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Wild Weather
Pg. 37 ADD BUT WAIT We first need to talk
about THE CORIOLIS EFFECT 1.) Northern
hemisphere -Air currents and ocean currents are
deflected to the right 2.) Southern hemisphere
-Air currents and ocean currents are deflected
to the left
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Wild Weather
Pg. 37-38 WHAT CAUSES WEATHER IN THE UNITED
STATES?? 1.) Global Wind Patterns(continued) Angle
of Earths tilt causes different amounts of
radiation to hit surface at different
points. Differential surface heating Produces
Cells of global air circulation Hadley - produce
deserts Ferrel - occur over continental masses
turbulence and jet stream variation create
severe weather conditions Polar cool air
sinks and moves toward equator But remember
Coriolis Effect
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Wild Weather

• Pg. 38
• Jet Stream - area of pressure gradient between
• cold polar air and warm subtropical air lots of
• atmospheric disturbance
• Occurs in troposphere(up high) hot airhigh
  pressure
• cold airlow pressure
• THIS IS OPPOSITE BAROMETRIC PRESSURE
• Coriolis bends the wind to the right/east
• MOVES LOTS OF AIRweather
• fast moving air (up to 370 mph)
• from 5 to 8 miles high
• moves from west to east over North America
• position changes due to seasons and turbulence

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Wild Weather
Pg. 38 3.) Fronts - Air masses have different
temperatures so dont mix, boundary
fronts Air masses in U.S. related to latitude
and relationship of ocean/land 3 types of
fronts Cold - cold air under warm, warm
moved upward thin band of intense
thunderstorms Warm - warm over wedge of cold
gentle gradient wide spread clouds Occluded
- 3 masses warm, cool and cold come together
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Wild Weather
Pg.38 4.) High and Low pressure
zones Barometric Pressure - measured by a column
of mercury
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Wild Weather
Pg. 38 Low Pressure - rising warm air creates low
pressure so air rushes in to replace rising air
produces counterclockwise surface winds air
moving upward cools, water vapor condenses
precipitation (stormy) ADD Two things
contribute or can cause rising air 1.) warm air
rises 2. divergence aloft creates a vacuum and
sucks up air from below BOTH cause upward
movement of airlow pressure
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Wild Weather
Pg. 38 Low Pressure (continued) Chicken or the
egg? Divergence or warm air? Usually working
together
Aloft air diverges Has to go some place
Warm Air rises
Barometer Effect?
Air Rushes in from side
Low Pressure Air rising
Ground
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Wild Weather
Pg. 38 Low Pressure (continued)
Top View
Coriolis Effects bends wind to Right (---)
Rushing in wind begins to blow from one arrow
to the next creating circular path-counterclockwi
se
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Wild Weather
Pg. 39 Cyclone - winds rotate counterclockwise
about a core of air moving upward Northern
Hemisphere-counterclockwise Low pressure-air
rises ND pg. 281 fig. 10.17 Generally occurs
in/downstream of trough of jet- divergence WHY???
13
Wild Weather
Pg. 39 High Pressure - air comes together in
upper atmosphere and descends and/or cold air
sinks Produces clockwise surface winds ADD
Two things can cause air to sink 1.)
convergence aloft crashing air aloft is forced
down 2.) cold air sinks
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Wild Weather
Pg. 39 High Pressure (continued) Chicken or the
egg? Divergence or cold air? Usually work together
Air converges aloft and is forced down
Cold Air Sinks
Barometer Effect?
Air hits ground and Rushes out to sides
High Pressure Air sinking
Ground
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Wild Weather
Pg. 39 High Pressure (continued)
Top View
Coriolis Effects bends wind to Right(---)
Rushing OUT air begins to bend to right and set
up clockwise rotation
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Wild Weather
Pg. 39 Descending air WARMS as it descends so
creates dry windy conditions no precip. (clear
weather) Anticyclone - winds moves clockwise
around downward moving air ND pg. 281 fig.
10.17 Generally occurs at ridge of jet-
Convergence WHY??
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Wild Weather
Pg. 38 GENERAL RULES Warm air rises Cold air
sink land dry ocean moist
TEMP? SUMMER -land is warmer WHY?? RAIN and
Storms? WHY??
Warm air rises OR divergence aloft Low pressure
Cold air sinks OR convergence High pressure
HEAVY RAIN
Land
Ocean
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Wild Weather
Pg. 38 GENERAL RULES Warm air rises Cold air
sink land dry ocean moist
TEMP? WINTER ocean is warmer WHY?? RAIN and
Storms? WHY?
Cold air sinks OR convergence High pressure
Warm air rises OR divergence aloft Low pressure
Light RAIN
Land
Ocean
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Wild Weather

• Pg.39
• MIDLATITUDE CYCLONES - (air mass rotating
• counterclockwise around a low pressure core)
• Produce most severe weather in U.S.-WHY???
• Three Scales of cyclones
• 1) LARGEST Jet stream weather system
• cold front behind warm front thunderstorms
• over large area DO FIRST ND pg. 281 fig. 10.17
• 2) Smaller localized can produce thunderstorms
• over smaller area
• 3) Tornado - smaller radius rotation of
• wind (higher speed winds)

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Wild Weather

• Pg. 40
• 6. Focus on THUNDERSTORMS
• HOW DO THEY WORK?
• warm moist air absorbs heat so less dense and
• rises (hot summer afternoons)
• as rises cools and water vapor condenses into
• clouds (as water condenses releases heat so
• rise even higher)
• ice and water becomes heavy updraft cant
• support so falls (precipitation) creating
  downdrafts
• that pull in cool air

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Wild Weather

• Pg. 40
• 6. Focus on THUNDERSTORMS
• HOW DO THEY WORK
• 4. updrafts and downdrafts occur in thunderstorm
• violent thunderstorm move ice up and down and
• create hail
• once downdraft pulls in a lot of cool air
  overwhelms updraft of warm air (no new moisture
  moved upward) and thunderstorm begins to die out
• 6. SUMMARY another summary

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Wild Weather
Pg. 40 MOST OCCUR WHERE? 1. Florida and inland
as tropical moist air moves off of Gulf
WHY??? 2. Mountains of western U.S. Moist Gulf
air contact dry desert air - moisture
moves up (mountains help force upward) and
you get a thunderstorm WHY????
Moist Air Forced aloft by low pressure Over land
Moist Air Forced aloft
Florida warm
Mountains
Ocean cool
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Wild Weather
Pg. 40 WHAT TYPE OF WEATHER DO THEY BRING? 1.
heavy rain - floods (TEXAS 22 INCHES IN 2 3/4
HOURS!!) and mass wasting Why Texas? - location
next to Gulf, air flow onto land over low-lying
coastal plain is moved up over highland created
by a fault system (warm air moved upwardprecip)
Moist Gulf Air sent aloft
Texas highlands
Low-lying coastal plains
fault
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Wild Weather

• Pg. 41
• flash floods in desert especially (S. Utah
  canyons)
• WHY?
• low vegetation
• hard surfaces
• thin soils
• topography-narrow passages
• 3. hail - nasty on crops - Texas again and
  Oklahoma (need colder air in interior for ice to
  form) largest 17 in diameter!!
• 4. lightning - starts forest fires and direct
  strikes cause deaths

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Wild Weather
Pg. 41 Lightning - a spectacular show in the
atmosphere Electric current seeks to balance
areas with excess charges cloud to cloud OR cloud
to earth Bottom of thundercloud builds negative
charge (due to colliding and shattering of
supercooled water drops)-not very well
understood The negative build up induces a
positive build up on the ground directly
below. ND Pg. 323 fig. 11.27 Diagram Awesome
site describing process
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Wild Weather
Pg. 41 Anatomy of Lightning step leaders
-Negative charge heads toward ground, when close
positive charges moves upward and they connect
and see flash. Animation Thunder results from
high temp of lightning flash (up to 55,000
degrees F) heats air and expands explosively
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Wild Weather

• Pg. 41
• winds
• SURFACE WINDS ALWAYS BLOW FROM
• HIGH TO LOW PRESSURE
• straight-line (derecho)
• rotating (tornado)- a little different than H
  to L
• straight-line wind up to 100 mph
• tornado wind speed up to 310 mph
• Small but deadly

Low Pressure
WIND
WIND
WIND
High Pressure
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Wild Weather
Pg. 42 WHAT MAKES A TORNADO?? (3 things) 1.)
humid warm air from Gulf gt75 degree F moves
north 2.) meeting fast gt50 mph cold dry air
3.) jet stream winds gt150 mph 4.) single
cell vs. super cell system ND pg. 326 fig.
11.30 When these air masses meet warm air is
lifted upward, strong updraft is sheared and spun
by fast-moving cold air and twisted at
upper levels by jet tornado ND pg. 326 fig.
11.29
Courtesy NOAA
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Wild Weather
Pg. 42 HOW DO THEY (TORNADOES) DESTROY? pressure
differences - very low pressure in
center, pressure inside a building is
much higher - when pressure outside
drops instantly - buildings explode. Utah-can
occur but rare. WHY?? SLC 1 fatality Kentucky/Ind
iana case Onset is rapid very little
warning. First siren warning at 149am. Second
at 159am tornado struck at 201am. F3(force3)
category. 158mph-206mph winds
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Wild Weather
ADD ON Tornadoes are classified based on wind
speed and resultant damage Fujita Scale Here
is a BIGGIE
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Wild Weather
Pg. 42 WHERE DO THEY OCCUR? Good Old
Okalahoma-WHY? Can happen in Utah
uncommon-WHY
VIDEO????