Page: 192 FIGURE 7.35 A microwave pulse is sent out from the radar transmitter. The pulse strikes raindrops and a fraction of its energy is reflected back to the radar unit, where it is detected and displayed, as shown in Fig. 7.36.

SEVERE THUNDERSTORMS (Chapter 14) A wall cloud associated with a supercell thunderstorm spins counterclockwise over the plains of Texas. Beneath the wall cloud, dust rising from the surface indicates that a tornado is about to form.

ORDINARY (“AIR MASS”) THUNDERSTORM LIFE CYCLE Page: 386 FIGURE 14.2 Simplified model depicting the life cycle of an ordinary cell thunderstorm that is nearly stationary as it forms in a region of low wind shear. (Arrows show vertical air currents. Dashed line represents freezing level, 0°C isotherm.)

SEVERE THUNDERSTORM 1 inch diameter hail, or 50 knot surface winds, or Page: 388 FIGURE 14.5 A simplified model describing air motions and other features associated with an intense multicell thunderstorm that has a tilted updraft. The severity depends on the intensity of the storm’s circulation pattern. 1 inch diameter hail, or 50 knot surface winds, or tornadoes

SEVERE THUNDERSTORM Page: 392 FIGURE 14.16 A side view of the lower half of a squall-line thunderstorm with the rear-inflow jet carrying strong winds from high altitudes down to the surface. These strong winds push forward along the surface, causing damaging straight-line winds that may reach 100 knots or more.

SEVERE THUNDERSTORM

SHELF CLOUD Figure 14.14 A dramatic example of a shelf cloud (or arcus cloud) associated with an intense thunderstorm. The photograph was taken in the Philippines as the thunderstorm approached from the northwest.

SHELF CLOUD Page: 389 FIGURE 14.8 A dramatic example of a shelf cloud (or arcus cloud) associated with an intense thunderstorm. The photograph was taken in central Oklahoma as the thunderstorm approached from the northwest.

SHELF CLOUD

ROLL CLOUD

ROLL CLOUD Page: 389 FIGURE 14.9 A roll cloud forms with a gust front.

SQUALL LINE THUNDERSTORM Page: 392 FIGURE 14.14 Pre-frontal squall-line thunderstorms may form ahead of an advancing cold front as the upper-air flow develops waves downwind from the cold front.

SQUALL LINE Page: 391 FIGURE 14.13 Doppler radar display superimposed on a map shows a pre-frontal squall line extending from Texas into Oklahoma and Arkansas during February 2011. Some of the thunderstorms embedded within the squall line (dark red and orange color) produced high winds, heavy rain, and large hail.

MESOSCALE CONVECTIVE COMPLEX (MCC) Page: 394 FIGURE 14.19 An enhanced infrared satellite image showing the cold cloud tops (dark red and orange colors) of a mesoscale convective complex extending from central Kansas across western Missouri. This organized mass of multicell thunderstorms brought hail, heavy rain, and flooding to this area. summer late night, early morning Midwest heavy rain, hail, high winds, flooding, tornadoes southerly, low-level jet (1.5 km above surface) (moisture and wind shear)

Derecho 1) Concentrated area of convectively induced wind damage/gusts greater than 50 knots (60 miles per hour) 2) The area must have a major axis length of 400 kilometers. 3) Wind reports should show a continuous and nonrandom pattern of occurrence. For instance, a swath of storms should consistently produce wind reports as the system moves to the east or southeast. 4) In the storm reported areas, at least three reports, separated by 64 km or more, should include wind gusts greater than 64 knots, or 74 mph. 5) A derecho is typically continuous and can sustain itself for hours. With that said, no more than three hours can elapse between successive wind damage events.

DRYLINE cP cT mT Page: 398 FIGURE 14.27 Surface conditions that can produce a dryline with intense thunderstorms.

Severe Thunderstorm Factors (Eagleman, 209)

THUNDERSTORM DAYS PER YEAR Page: 402 FIGURE 14.30 The average number of days each year on which thunderstorms are observed throughout the United States and southern Canada. (Due to the scarcity of data, the number of thunderstorms is underestimated in the mountainous far west.)

HAIL DAYS PER YEAR Page: 402 FIGURE 14.31 The average number of days each year on which hail is observed throughout the United States and southern Canada.

TORNADO! (Chapter 15) Figure 14.32 A mature tornado with winds exceeding 150 knots rips through southern Illinois.

Ideal Tornadic Thunderstorm Conditions jet stream trough westerlies aloft (cP) southerly low-level jet (mT) Page: 397 FIGURE 14.25 Conditions leading to the formation of severe thunderstorms, and especially supercells. The area in yellow shows where severe thunderstorms are likely to form. warm sector

Tornadic Thunderstorm Vertical Profile (cP) Page: 398 FIGURE 14.26 A typical sounding of air temperature and dew point that frequently precedes the development of supercell thunderstorms. The thickness of the warm, moist air from the surface up to the cap at 800 mb is usually on the order of about 2000 m or 6000 ft. (An actual sounding on the day that a severe thunderstorm tore through Moore, Oklahoma, May 20, 2013, is shown in Fig. 13.4 on p. 353.) (mT)

VERTICAL WIND SHEAR AND VORTEX TUBE Page: 426 FIGURE 15.15 (a) A spinning vortex tube created by vertical wind shear. (b) The strong updraft in the developing thunderstorm carries the vortex tube into the thunderstorm producing a rotating air column that is oriented in the vertical plane.

TORNADIC THUNDERSTORM CHARACTERISTICS FIGURE 14.19 Some of the features associated with a classic tornado-breeding supercell thunderstorm as viewed from the southeast. The storm is moving to the northeast.

TORNADIC THUNDERSTORM CHARACTERISTICS Page: 427 FIGURE 15.17 A classic mature tornadic supercell thunderstorm showing updrafts and downdrafts, along with surface air flowing counterclockwise and in toward the tornado. The flanking line is a line of cumulus clouds that form as surface air is lifted into the storm along the gust front. (Note: Supercell thunderstorm is NOT at proper scale as drawn above)

Conservation of Angular Momentum angular momentum=mass x velocity x radius

Wall Cloud FIGURE 14.20 A wall cloud photographed southwest of Norman, Oklahoma.

April 3-4, 1974 Super Outbreak

# TORNADOES PER 10,000 SQ. MILES PER YEAR Page: 418 FIGURE 15.5 The average annual number of observed tornadoes per 10,000 square miles in each state from 1991 to 2012. (Data from NOAA) “Tornado Alley”

TORNADO TRACKS, 1950–2013 (SOURCE: NOAA)

AVERAGE U.S. TORNADOES BY MONTH (2000–2010) Page: 418 FIGURE 15.6 Average number of tornadoes during each month in the United States from 2000 to 2010.

JET STREAM AND TORNADO ACTIVITY Summer Jet Spring/Fall Jet Winter Jet

Number of U.S. Tornadoes per Year Page: 417 FIGURE 15.4 Total number of tornadoes reported in the United States for each year from 1952 to 2012 (blue bar); and the total number of strong tornadoes with winds exceeding 117 knots or 135 mi/hr reported during the same period (red line). (Note: Tornadoes that occurred before the introduction of the Enhanced Fujita (EF) Scale in 2007 have been converted to the new scale.)

FUJITA TORNADO SCALE (Used damage to infer windspeeds)

ENHANCED FUJITA TORNADO SCALE (Considers structure type and wind observations)

Rotary windspeed=100 kts. Forward speed=50 kts. At “D,” they are added Page: 420 FIGURE 15.8 The total wind speed of a tornado is greater on one side than on the other. When facing an onrushing tornado, the strongest winds will be on your left side. At “D,” they are added At “B,” they counteract each other

Page: 420 FIGURE 15.9 A powerful multi-vortex tornado with three suction vortices.

EF 5, Joplin, MO, 2011

EF 5, Joplin, MO, 2011

Sharknado