1. Extreme Weather and Climate Events
Blizzards, Thunderstorms, Hurricanes, Floods, and Drought

2. Why Look at Extreme Events?
Can harm human and natural systems both during and after event
Economic losses
Occurrence may be affected by human activity according to various studies, including IPCC, 2001

3. Blizzards
A strong winter storm with cold temperatures, strong winds, and intense falling or blowing snow
Rarely experienced in US below ~ 35°N
Types
Longwave cyclone: low pressure centers both at surface and in upper atmosphere; move very slowly; affect northern portions of US; usually in spring
Trough cyclone: develops in association with trough in jet stream; then upper-air features strengthen low pressure at surface; move faster; typically along eastern coast of US (nor’easters); any time during winter

4. Features Associated with Blizzards
Low pressure, fronts
Cold temperatures (usually < 20°C (-6°F))
Strong winds (> 35 mph)
Intense falling or blowing snow
Sleet and freezing rain south of snow
Sometimes rain even farther south
Low visibility due to falling/blowing snow
“Whiteout” conditions

5. Problems Associated with Blizzards
Economic loss – businesses closed
Death – due to exposure, accidents, etc.
Other health problems – hypothermia, frostbite
Utility complications
Structural damage – weight of snow
Travel inconvenience – closed airports, closed highways, accidents

6. A Few Examples Montana (March 1969) Eastern US (January 1978)
20+” (45+cm) of snow
Trough cyclone
Eastern US (January 1978)
Lowest central pressure = 958 mb, winds to ~ 90 mph, almost 100 deaths
Longwave cyclone
Storm of the Century – eastern US (March 1993)
Lowest central pressure = 960 mb, up to 56” of snow (Tenn.), 24” in Mtn. City, Georgia, winds > 75 mph
Every major East Coast airport closed, 3 million customers with no electricity, roofs collapses
In Florida – 27 tornadoes, 3 m storm surge
In total, ~ 270 deaths and > $3 billion in damage

7. Thunderstorms
A strong local storm that contains intense updrafts and downdrafts, lightning, and thunder
Capable of producing flooding, strong winds, hail, and tornadoes
Severe if produces any/all of following
Hail > 0.75” (1.9 cm)
Wind > 57 mph (50 knots, 92 km/hr)
Tornado

8. Some Features in Thunderstorms
Overshooting top – intense updrafts push cloud into stratosphere (top > ft)
Hail – chunks of ice that grow inside a storm due to internal circulation; most common in Great Plains
Microburst – strong winds at surface produced when precip pulls air with it (leading edge at surface called gust front)
Lightning – series of huge “sparks” caused by differing electrical charges
Thunder – sound waves produced by rapid expansion of air due to heat from lightning
Tornadoes...

9. A Few Examples Tri-State Outbreak (March 18, 1925)
Missouri, Illinois, and Indiana
7 tornadoes over ~ 440 mi (700km), 695 deaths
Palm Sunday Outbreak (1965)
Midwest US
30 tornadoes in 5 states, 256 deaths
Topeka, KS (June 8, 1966)
16 deaths, hundreds of houses destroyed or damaged, Washburn University badly damaged

10. A Few More Examples Lubbock, TX (May 11, 1970)
26 deaths, > $100 million in damage
Weather observer records
April 3-4 Outbreak (1974)
13 states (central AL to s. MI, central IL to central VA)
16 hrs, 148 tornadoes, 307 deaths, > 6000 injuries, approximately $600 million in damage
Central Oklahoma Outbreak (May 3, 1999)
~ 74 tornadoes through Oklahoma
In OKC, estimated$1.2 billion in damage, 41 deaths, 675+ injuries (winds estimated at 300 mph)

11. Floods
Condition in which water cannot be drained adequately by (1) stream discharge to prevent overflow of channel banks or (2) infiltration, runoff, or evaporation to prevent excessive “ponding” on the surface
North Atlantic region most prone region in US

12. Causes of Floods
Excessive precip over brief period (flash flood) or extended period (as in a hurricane)
Moderate precip over extended period (slow moving cyclone, repeated passing of cyclones, stationary front, “training” of thunderstorms)
Snowmelt (in spring, combined with rain)
Dam or levee breakage

13. Rillito River (July 2006)

14. Rillito River (July 2006)

15. Problems Associated with Floods
Water supply
Agricultural and other economic losses
Water-born diseases
Human and animal deaths (drowning, electrocution)
Travel inconveniences
Fire

16. A Few Examples Much of East Coast (1972) – Agnes
Big Thompson Canyon (1976)
Due to thunderstorm (12” (30.5cm) in 4 hours!)
135 deaths, $35.5 million in property damage
Mississippi River, a.k.a. The Great Flood (1993)
Due to repeated passing of cyclones
50 deaths, 70,000 evacuated, $12 billion in property damage
California (summer 2004)
Due to levee breakage

17. Drought
Definition varies depending on agricultural or hydrological considerations
Deficiency of water normally obtained from precip
Various monitors exist, one of which is the Palmer Drought Severity Index (PDSI) – updates available on Internet
Causes
Weather/climate-related
Lack of rainfall
Strong winds
Teleconnections

18. Drought (cont’d) Causes (cont’d) Associated problems
Human-induced aggravation
Poor farming practices
Increased population
Expansion of civilization
Removal of vegetation
Excessive water usage
Associated problems
Water supply
Agricultural and other economic losses
Landscape changes
Death
Fire
Dust storms

22. A Few Examples The Dust Bowl (1930s)
Western and central US (early to mid-1950s)
Northeastern US (early 1960s)
Sahelian Drought ( )
California ( )
Northeastern US (late ’90s to early 2000s)
Much of western US (~2000 to present)