meteorology test number 4

Long-Range Forecasting of Atlantic Hurricanes

* Since 1980s, Prof. William M. Gray and colleagues at Colorado State University issue seasonal hurricane activity forecasts for Atlantic basin * NOAA also issues a Seasonal Outlook for Atlantic basin hurricane activity * Gives probabilities of overall seasonal activity compared to normal * Likely ranges of named tropical cyclones, hurricanes, major hurricanes * Accumulated Cyclone Energy (ACE)

Hurricane Threat to the Southeast

* Infrequency in major hurricanes in the 1970-80s * Lulled many coastal residents of the southeast U.S. into a false sense of security and * Encouraged coastal development and growth * In 2005, the coast is home to 53% of all Americans * Population growth is most rapid from Texas through the Carolinas, especially in Florida * Public safety officials are concerned about the trend toward more Atlantic tropical cyclones Barrier islands particularly at risk * Barrier island - elongated, narrow accumulation of sand oriented parallel to the coast and separated from the mainland by a lagoon, estuary, or bay * Facing open ocean, they absorb the brunt of ocean storms * Atlantic City, NJ, Miami Beach, FL, and Virginia Beach, VA are built entirely on barrier islands * Evacuations critical

Hurricane Modification

* Project STORMFURY (1961-1983) * Spurred by 6 destructive hurricanes that affected U.S. East Coast during the mid-1950s * Working hypothesis: seeding hurricanes with silver iodide crystals would reduce wind strength * Supposed to increase latent heat, enhance convection just beyond the eye wall * Assumed a new eyewall would then form farther out, and the hurricane's circulation would theoretically weaken * Any successes dismissed * Convective clouds in hurricanes found to have too little supercooled water for seeding to be effective

Tornado alley is

*a. Texas-Oklahoma-Kansas-Nebraska-South Dakota.

Nocturnal radiational cooling is most intense

*a. at the center of an anticyclone.

In the southern Great Plains, tornadoes are most likely to develop when

*a. dry Pacific air overlies a layer of maritime tropical air.

The most important force operating in a tornado is (the)

*a. pressure gradient force.

Hurricanes rarely form off the coast of South America primarily because of

*a. shear produced by strong winds in the middle and upper troposphere.

A downburst is designated a microburst or macroburst depending on

*a. the distance impacted along the ground.

Less than ______ of all thunderstorms produce tornadoes.

1%

Sustained surface winds in a hurricane are

119 km per hour (74 mph) or higher.

The only year on record in which major hurricanes were reported in all 6 months of the Atlantic hurricane season was

2008

thunderstorm life cycle

3 stages. Cumulus stage: dominated by updraft, precipitation forming but not yet falling. Mature Stage: warm updraft, cold downdraft; precipitation falling; liquid and ice in cloud; lightning and thunder. Dissipating stage: cold pool of air at bottom, warm air at top- the storm has stabilized the environment; rain falls through cloud. look at models.

Tropical cyclone formation requires a sea-surface temperature of at least 26.5 °C through an ocean depth of at least ______ meters.

45

The most intense tornadoes are rated ______ on the EF-scale.

5

There are hallmark signatures that characterize most supercell thunderstorms:

A mesocyclone, which is a rotating updraft that displays as a rotational couplet and 2) A hook echo, which is created by precipitation echoes wrapping around the mesocyclone.

Server thunderstorms model

A synoptic weather pattern that favors development of severe thunderstorms. The dryline is the western boundary of the mT air mass and brings about uplift in a manner similar to a cold front. A temperature sounding that favors the development of severe thunderstorm cells. • A capping inversion separates subsiding dry air aloft from warm, humid air near the surface.

Thunderstorm tracking

A thunderstorm often tracks at an angle to the path of its constituent cells. Squall lines organize and can stretch across the U.S. (technical name is QLCS = quasi-linear convective system)

Tornadoes

About 1,000 severe thunderstorms produce tornadoes in the U.S. each year (about 10% of all severe thunderstorms).Peak activity is in May and June. All 50 states have been hit by tornadoes. Average speed is 30 mph

The cloud and precipitation shield associated with a warm front typically is ______ the cloud and precipitation shield associated with a cold front.

Broader than

Evacuation

Coastal evacuation plans tested in 1985 * Category 3 Hurricane Elena (bottom figure) followed an erratic path over the Gulf * Downside of evacuation * During Hurricane Floyd in 1999 * 2 million were evacuated and massive gridlock occurred * Greater the uncertainty with forecast track, broader the evacuation zone and greater economic losses * Cost of evacuation ~$1 million/mi of coastline * Vertical evacuation may be an option * Other strategies to minimize loss of life and property: * Elimination of federal floodplain insurance * Preservation of mangrove swamps * Stringent building codes Home designed so 'first floor' is floodable. Actual house supported by anchored beams.

EF-2.

Considerable damage: est. wind 111-135 mph. Most single- wide mobile homes destroyed. Permanent homes can shift off foundation. Flagpoles collapse. Softwood trees debarked.

Usually air mass modification is most rapid when

Continental polar air moves over bare ground

The tropics

Day/night (diurnal) temperature changes are typically larger than seasonal changes • Humid, warm (mT) air • Fronts not present • The ITCZ, and the thunderstorm activity it generates, follows the subsolar latitude • Isobars are not much use in the tropics (unlike at mid-latitudes), since the pressure doesn't vary much • Streamlines are curves that are parallel to the wind direction; they are useful in tropical meteorology

EF-4.

Devastating damage: est. wind 166-200 mph. Complete destruction of well-built residences, large sections of school buildings.

Hurricane Characteristics

Haracan": storm god ("spirit of mayhem") of the Taino People, who lived on today's Haiti/Dominican Republic and nearby islands in 1492 • Via Spanish, the Taino also gave us the words "barbecue", "banana", "potato", "tobacco" Atlantic: Hurricane Pacific: Typhoon (Cantonese tai-fung "great wind") Indian Ocean, Australia: Cyclone (Greek kyklos "circle") • Hurricane: cyclone with 74 mph or higher sustained wind speed (sustained: 1-min avg, measured at 10 m altitude) • Compared to extra-tropical cyclones, hurricanes have much lower sea-level central pressure, and much larger horizontal pressure gradient and smaller in scale •Seasonal because need high sea- surface temp. SST > 26.5°C (80°F) in a layer 45 m deep or more •SST peaks 6-8 weeks after maximum solar radiation •Peak formation is mid-August to late October; official hurricane season runs the half year from 1 June to 30 November The above pic: SST in June (yellow is hottest) •NOTE: Text emphasizes role of water vapor and latent heat. In fact, hurricane modelers have done computer simulations of dry hurricanes---the important energy input is the surface heating itself, not the latent heat (water vapor).

Hurricane Hazards

Heavy rains and inland flooding * Freshwater flooding was responsible for 60% of deaths from 1970 - 1999 attributed to tropical cyclones or their remnants * Strong winds * Responsible for 12% of deaths during the same period * Tornadoes * Storm surge * Caused most of the 1,500 fatalities associated with Hurricane Katrina * Potentially most dangerous hazard Inland Flooding - Hurricane Irene * Became hurricane 21 August, 2011 * Est. 56 dead in Caribbean and US * $3.1 billion damages in Caribbean * $15.6 billion in U.S. * Storm Surge * 1.4 m (4.56 ft) at Sewells Point, VA, and the Battery in NYC * 13-38 cm (5-15 in) heavy rainfall * 2.8 m (9.21 ft) above flood stage in Rutland, VT Storm surge * A dome of ocean water 80 - 160 km (50 - 100 mi) wide that sweeps over the coastline near the hurricane's landfall * Caused by strong winds and low barometric pressure * Most likely on the side of the hurricane with onshore winds * Structural damage caused by wind-driven waves on top of the dome of water, armed with floating debris

Necessary Conditions for Thunderstorm

Humid Air: in bottom half of troposphere (often mT air: maritime tropical). Atmospheric Instability: the more humid the air, the lower the convective condensation level (CCL) and the more unstable the atmosphere. Source of Uplift: horizontal convergence, fronts, mountain slopes

EF-5.

Incredible damage: est. wind above 200 mph. Significant structural deformation of mid- and high-rise buildings.

The time of year when a lake breeze is most likely to develop along the Lake Michigan shoreline is

June

What Causes a Severe Thunderstorm?

Key: vertical wind shear (change in horizontal wind with altitude) • The gust front cannot push the humid air far from the cell • Most precip. falls alongside the tilted updraft, rather than through it • The shear cannot be too strong, or it will tear cumulonimbus apart

In summer, at the same pressure, maritime tropical air is ______ continental tropical air. a. more dense than

Less dense than

EF-0

Light damage: est. wind 65-85 mph. Causes damage to siding and shingles

Thunderstorm Hazards

Lightning, Downbursts, Derecho, Flash Floods, Hail

Severe Thunderstorms

Local damaging surface winds over 50 kts (58 mph), and/or large hail over 3⁄4 in. (1.9 cm) • Frequent lightning • May produce flash floods • May produce tornadoes

Contrasting air masses are brought together to form fronts by the surface winds blowing about the center of a ______ pressure system.

Low

EF-1.

Moderate damage: est. wind 86-110 mph. Considerable roof damage. Winds can uproot trees and overturn single-wide mobile homes. Flagpoles bent.

Storm surge

Prior to 1970, was responsible for the majority of hurricane- related fatalities. * 1895 unnamed hurricane killed an estimated 2,000, and left 20,000 to 30,000 homeless * 8000 people died in most deadly U.S. natural disaster: 4.6 m storm surge hit Galveston, TX, in 1900 * Hurricane Camille (1969) produced a 7.3 m (24.3ft) surge at Pass Christian, MS * Awareness, warnings and evacuation (since 1970) have increased survival * From 1970 to 1999, there were only 6 storm surge deaths. * East Pakistan (now Bangladesh) in 1970 - storm surge killed ~300,000

Necessary Conditions for Hurricanes

Relatively high sea-surface temperatures (SST) * Adequate Coriolis Effect to create the spin * With rare exception, tropical cyclones do not form within 5 degrees of the equator * Weak vertical wind shear * Allows cluster of cumulonimbus to form * Wind shear would tear these apart * Relatively humid air in the mid-troposphere

EF-3.

Severe damage: est. wind 136-165 mph. Hardwood trees debarked. All but small portions of houses destroyed.

Tornado thunderstorm connection

Supercells produce most of the violent tornadoes • Updrafts can exceed 150 mph • Horizontal rotation is tilted vertically by updraft, forming a mesocyclone • A portion of the rain-free base of the thunderstorm accompanies the mesocyclone, called a wall cloud • Most wall clouds do not produce tornadoes • Tornadic wall clouds have strong, persistent rotation before the appearance of a tornado • A tornado typically appears near the updraft and toward the rear of a supercell

Hurricane characteristics

The eye is at the center of a hurricane * Almost cloudless skies, subsiding air, light winds * Diameter ranges from 10 to 65 km (6 to 40 mi) * Eye shrinks as hurricane intensifies * The eye wall * Borders the eye of a mature storm * Ring of cumulonimbus clouds produce heavy rains and strong winds * On the side of the advancing system the wind blows in the same direction as the storm's forward motion, the most dangerous part of a hurricane * In the Northern Hemisphere, this is on the right side of the hurricane when facing in the direction of the system's forward motion * Cloud bands spiral inward towards the eye wall and produce heavy convective showers and hurricane-force winds * At high altitudes, cirrus or cirrostratus spiral outward

supercell thunderstorms

The updraft and downdraft are tilted and are thereby separated from each other.

MCS

Thunderstorms are mesoscale convection systems. classified based on the number, organization, and intensity of their constituent cells * Occur as single cells, multi-cellular clusters, and supercells

The ______ of the life cycle of a thunderstorm cell is characterized by mostly updrafts.

Towering cumulus stage

Hurricane Life Cycle

Tropical Depression * Maximum sustained winds reach 37 km per hr (23 mph) or higher * Tropical Storm * Winds reach at least 63 km per hr (39 mph) * Assigned a name * Hurricane * Winds reach 119 km per hr (74 mph) or higher * As storm weakens, it is downgraded by reversing this classification system

When sustained winds in an intensifying tropical disturbance reach 37 km per hr or higher, the storm system is called a

Tropical depression

Hurricane Origins

Weak vertical wind shear is needed for hurricanes to form, less than 23 mph from surface to upper troposphere •This allows a cluster of cumulonimbus clouds to organize over tropical seas, becoming a tropical disturbance • During El Niño, Atlantic hurricanes are infrequent because of too- strong vertical shear. For example, during the intense El Niño of 1997 only 3 hurricanes formed • Worldwide, an average of 88 tropical cyclones become strong enough to be named. About half of these reach hurricane strength. •Between 1931 and 2004, 10.2 named tropical storms formed in the Atlantic area that affects the U.S. (including the Caribbean and Gulf of Mexico)

A hurricane differs from a mature extratropical cyclone in that a hurricane

a. has no fronts. b. develops within a uniform warm and humid air mass. c. is more intense but smaller. d. is a warm-core system. *e. All of the above are correct.

A dryline

a. is a likely site for development of a severe thunderstorm cell. b. separates hot, dry air from warm, humid air. c. often occurs over Texas and Oklahoma. *d. All of the above are correct.

The eye of a hurricane typically

a. shrinks in diameter as the hurricane intensifies. b. features subsiding air. c. is surrounded by a ring of cumulonimbus clouds (the eye wall). *d. All of the above are correct.

Condition needed for the development of a tornadic circulation within a thunderstorm:

a. strong updraft. b. strong vertical shear in the horizontal wind. c. development of a mesocyclone. *d. All of the above are correct.

A tropical cyclone breeding ground:

a. the Indian Ocean east of Madagascar b. the Arabian Sea c. the Bay of Bengal d. the Gulf of Mexico *e. All of the above are correct.

A tropical disturbance may be triggered by

a. the intertropical convergence zone (ITCZ). b. a trough in the westerlies intruding into low latitudes. c. an easterly wave. *d. Any of the above is correct.

As a hurricane tracks inland, its

a. winds diminish. b. central pressure rises. c. rains continue and may be heavy. d. horizontal pressure gradient weakens. *e. All of the above are correct.

As a chinook wind is drawn down the leeward slopes of a mountain range,

all of the above

Thunderstorm cells associated with a fast-moving, well-defined cold front

all of the above are correct often occur as a squall line parallel to and ahead of the front. c. often form an elongated cluster parallel to the front.

A mesoscale convective complex (MCC)

all of the above are corrects not associated with a front. b. usually covers a large area, perhaps the size of a state. c. is primarily a warm-season phenomenon.

A dust devil

all of these are correct

The first sign that a hurricane may be developing over tropical seas is the appearance of

an organized cluster of cumulonimbus clouds.

A(n) __________ is often situated above a hurricane.

anticyclonic air flow

Thunderstorm development is triggered by

any of the above are correct uplift along a well-defined cold front. b. converging surface winds. c. uplift of warm, humid air along mountain slopes. d. forced convection.

The anvil top of a thunderstorm cloud is likely to be a ______ cloud that is composed of ______.

cirrus..... ice crystals

overshooting tops

clusters of intense thunderstorm cells appear as bright....

A Siberian high is an example of a ______ anticyclone.

cold-core

The northwest sector of a mature extratropical cyclone is usually the __________.

coldest

towering cumulus stage

cumulus clouds build vertically, driven by buoyancy from latent heat release. surge upward to altitudes of 8-10 km over 10-15 min. updrafts are strong enough to keep the liquid droplets and ice crystals suspended- no precipitation. Free convection: triggered by intense solar heating; usually not powerful enough on its own to produce thunderstorms. Forced Convection: Converging winds strengthen convection, as does orographic uplift. Generally, forced convection is the cause of thunderstorms.

A mountain breeze blows

downslope at night

In a mature extratropical cyclone, fog and drizzle are most likely to develop

in the cold air just above the surface warm front

In the United States over the 30-year period from 1970 to 1999, the majority of tropical cyclone- related fatalities was due to

inland fresh water flooding

Supercell Thunderstorm

large, intense cell with rotation, may generate a tornado

An occluded front forms

late in the cycle of an extratropical cyclone

The principal source of energy that sustains the circulation of a hurricane in the tropics is

latent heat

At the same pressure, which one of the following air masses is least dense?

maritime tropical

A tropical storm or hurricane develops in __________ air.

maritime tropical mT

Mesocyclone Convective Complex (MCC):

nearly circular cluster of interacting cells. Lifetime 6 hrs up to 12-24 hrs Warm-season phenomenon: March to September. Usually develop at night, with no associated front. Humid air fed by a low-level jet.

Of the nearly 1300 or so tornadoes that strike the United States each year, perhaps ______ will be rated EF5.

only 1

Dissipating Stage

precipitation and the downdraft spread throughout the thunderstorm cell. the supply of moisture is cut off as subsiding air replaces the updraft. adiabatic compression warms the subsiding air and the clouds gradually vaporize. the local environment is left in a stable condition.

By convention, the mature stage of the life cycle of a thunderstorm cell begins when

precipitation first reaches earth's surface

Along the track of an extratropical cyclone, the area to the right of the system's forward motion is

relatively warm

thunderstorm classification

single cell, multi cell cluster, multi cell line, supercell. Weakest to strongest.

The warmest sector of a mature extratropical cyclone is usually __________ of the cyclone center.

southeast

most server

squall line, quasi-linear convection system QLCS: elongated cluster of thunderstorm cells accompanied by a continuous gust front at the leading edge. Typically develop in warm southeast sector of a mature extra tropical cyclone

The horizontal air pressure gradient is ______ in a hurricane than in a typical extratropical cyclone.

steeper

Historically, the most destructive aspect of a hurricane striking a low-lying coastal area:

storm serge

Mature stage

tropopause arrests upward motion, causes anvil to form. frequent lighting, 20-30 duration. weight of droplets, ice crystals overcomes updrafts, precipitation starts, can be heavy. rain causes downdraft. dry air mixed into downdraft (entrained) causes evaporative cooling, which enhances the downdraft. Gust Front: small cold front formed by leading......

Appearance of cirrus clouds indicates ______ air advection aloft.

warm

Thunderstorms that produce flash floods form in an atmosphere with ______ vertical wind shear and ______ moisture.

weak....abundant

Saffir-Simpson Hurricane Intensity Scale

• Cat 1: minor damage to piers, mobile homes • Cat 2: roof damage, small boats break free of moorings • Cat 3: large trees blown down, some flooding • Cat 4: lost roofs, beach erosion, major flooding, evacuation • Cat 5: building failures, major flooding, massive evacuation • 100 to 300 times greater damage from a Cat. 4 or 5 hurricane compared to a Cat. 1

Hurricane Paths

•Tropical cyclone trajectories are often erratic •They typically drift northwestward and then curve northeastward when they reach the western Atlantic • Hurricanes that track the warm Gulf Stream can maintain their tropical characteristics far up the Atlantic coast • Otherwise, when they cross about 30°N, colder air is drawn in, fronts develop, and they acquire extra-tropical characteristics