Extreme Weather and Climate Events

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) • 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 > 70 000 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) • 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 (1968-1974) • California (1976-1977) • Northeastern US (late ’90s to early 2000s) • Much of western US (~2000 to present)