Wednesday April 18, 2012 (Wind Speeds of Hurricanes and Tornadoes; Weather Fronts)

The Launch Pad Wednesday, 4/18/12 Define the term “air mass.” A very large body of air, covering thousands of square miles, that contains similar temperature and humidity conditions throughout.

Assignment Currently Open Summative or Formative Date IssuedDate Due Date Into Grade Speed Last Day WS – The Structure of the Atmosphere F4/44/10 Activity – Write Test Questions on Atmospheric Heating S4/10 Quiz 26S4/13 Activity – Write Test Questions on Cyclones and Anticyclones S4/17

Announcements I will be available after school today until 5:15.

Latest News Greenland May Be Slip-Sliding Away Due to Surface Lake Melting Click below for article:

Wind Speeds of Tropical Depressions and Tropical Storms Tropical Depression A tropical depression is a tropical cyclone in which the maximum sustained wind speed is up to 33 kt (38 mph, 17 m/s). Depressions have a closed circulation.

Wind Speeds of Tropical Depressions and Tropical Storms Tropical Storm A tropical storm is a tropical cyclone in which the maximum sustained surface wind speed ranges from 34 kt (39 mph,17.5 m/s) to 63 kt (73 mph, 32.5 m/s). The convection in tropical storms is usually more concentrated near the center with outer rainfall organizing into distinct bands.

Saffir-Simpson Hurricane Wind Scale

Category 1 Hurricane

Category 2 Hurricane

Category 3 Hurricane

Category 4 Hurricane

Category 5 Hurricane

The Enhanced Fujita Tornado Scale (EF Scale) EF-0. Light damage Wind 65 to 85 mph. Causes some damage to siding and shingles EF-1. Moderate damage Wind 86 to 110 mph. Considerable roof damage. Winds can uproot trees and overturn single-wide mobile homes. Flagpoles bend. EF-2. Considerable damage Wind 111 to 135 mph. Most single-wide mobile homes destroyed. Permanent homes can shift off foundation. Flagpoles collapse. Softwood trees debarked. EF-3. Severe damage Wind 136 to 165 mph. Hardwood trees debarked. All but small portions of houses destroyed. EF-4. Devastating damage Wind 166 to 200 mph. Complete destruction of well-built residences, large sections of school buildings. EF-5. Incredible damage Wind above 200 mph. Significant structural deformation of mid- and high-rise buildings.

EF 1 Tornado

EF 2 Tornado

EF 3 Tornado

EF 4 Tornado

EF 5 Tornado

Weather “Fronts” cold frontwarm frontstationary front occluded front surface trough squall linedry linetropical wave

Cold Fronts A cold front is located at the leading edge of the temperature drop off, which in an isotherm analysis shows up as the leading edge of the isotherm gradient, and it normally lies within a sharp surface trough. Cold fronts can produce sharper changes in weather and move up to twice as quickly as warm fronts, since cold air is denser than warm air and rapidly replaces the warm air preceding the boundary. On weather maps, the surface position of the cold front is marked with the symbol of a blue line of triangle-shaped pips pointing in the direction of travel, and it is placed at the leading edge of the cooler air mass. Cold fronts come in association with a low pressure area. The concept of colder, dense air "wedging" under the less dense warmer air is often used to depict how air is lifted along a frontal boundary. The cold air wedging underneath warmer air creates the strongest winds just above the ground surface, a phenomena often associated with property-damaging wind gusts. This lift would then form a narrow line of showers and thunderstorms if enough moisture were present.

Cold Front

Warm Fronts Warm fronts are at the leading edge of a homogeneous warm air mass, which is located on the equator ward edge of the gradient in isotherms, and lie within broader troughs of low pressure than cold fronts. A warm front moves more slowly than the cold front which usually follows because cold air is denser and harder to remove from the Earth's surface. This also forces temperature differences across warm fronts to be broader in scale. Clouds ahead of the warm front are mostly stratiform, and rainfall gradually increases as the front approaches. Fog can also occur preceding a warm frontal passage. Clearing and warming is usually rapid after frontal passage. If the warm air mass is unstable, thunderstorms may be embedded among the strati form clouds ahead of the front, and after frontal passage thundershowers may continue. On weather maps, the surface location of a warm front is marked with a red line of semicircles pointing in the direction of travel.

Warm Front

Stationary Fronts A stationary front is a non-moving (or stalled) boundary between two air masses, neither of which is strong enough to replace the other. They tend to remain essentially in the same area for extended periods of time, usually moving in waves. [10] There is normally a broad temperature gradient behind the boundary with more widely spaced isotherm packing. [10] A wide variety of weather can be found along a stationary front, but usually clouds and prolonged precipitation are found there. Stationary fronts either dissipate after several days or devolve into shear lines, but they can transform into a cold or warm front if conditions aloft change. Stationary fronts are marked on weather maps with alternating red half-circles and blue spikes pointing in opposite directions, indicating no significant movement.

Stationary Front

Occluded Fronts An occluded front is formed when a cold front overtakes a warm front. The cold and warm fronts curve naturally poleward into the point of occlusion, which is also known as the triple point It lies within a sharp trough, but the air mass behind the boundary can be either warm or cold. In a cold occlusion, the air mass overtaking the warm front is cooler than the cool air ahead of the warm front and plows under both air masses. In a warm occlusion, the air mass overtaking the warm front is warmer than the cold air ahead of the warm front and rides over the colder air mass while lifting the warm air. A wide variety of weather can be found along an occluded front, with thunderstorms possible, but usually their passage is associated with a drying of the air mass. Occluded fronts are indicated on a weather map by a purple line with alternating half-circles and triangles pointing in direction of travel. Occluded fronts usually form around mature low- pressure areas.

Occluded Front

Weather Station Models

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Weather Station Models ??

Dew Point The dew point is the temperature where the water vapor in a volume of humid air at a constant barometric pressure will condense into liquid water. Condensed water is called dew when it forms on a solid surface. The dew point is a water-to-air saturation temperature. The dew point is associated with relative humidity. A high relative humidity indicates that the dew point is closer to the current air temperature. Relative humidity of 100% indicates the dew point is equal to the current temperature and that the air is maximally saturated with water. When the dew point remains constant and temperature increases, relative humidity decreases.