April 29th-Weather Fronts and Thunderstorms

Cold Fronts vs. Warm Fronts

• The primary distinction between cold and warm fronts lies in their direction of travel.
  • Cold Front: Cold air displaces warmer air.
  • Warm Front: Warm air displaces colder air.
• If a cold front reverses direction, it becomes a warm front, and vice versa. The relative warmth of the air mass dictates the front type.

Physical Characteristics and Density Differences

• Colder air is denser than warmer air.
• Cold Fronts:
  • As a cold front advances, it forces warmer air to rise rapidly, creating a steep boundary or slope.
  • This rapid lifting leads to quick cooling, condensation, and precipitation near the front.
  • The onset of a cold front is characterized by rapid cloud formation, precipitation, and a temperature drop in a short time frame.
• Warm Fronts:
  • Warm air gradually rides over colder air, resulting in a gentler slope.
  • Cloud formation and precipitation can occur far ahead (up to hundreds of miles) of the surface warm front.
  • Surface temperature changes lag cloud formation and precipitation, with temperature increases occurring after these initial signs.

Cloudiness and Precipitation Patterns

• Cold Front: Expect rain and cloudiness directly along the front.
• Warm Front: Expect cloudiness to precede the front.

Real-World Weather Patterns

• Classic weather patterns involve a cold front advancing from the north and a warm front pushing up from the south.
• Air mass types associated with fronts:
  • Maritime Polar (MP)
  • Continental Polar (CP)
  • Maritime Tropical (MT): Contains significant water vapor and energy.

Frontal Positions and Weather

• Weather patterns typically align along cold and warm fronts and ahead of warm fronts.
• Precipitation can occur broadly due to the uplift of moist air over cooler landmasses.

Expected Understanding

• Understand the differences between warm and cold fronts, including associated weather patterns.
• Recognize that cloudiness and precipitation can precede surface temperature changes with warm fronts.
• Understand that cold fronts can cause rapid weather changes due to the sharp uplift of warm air.

Air Mass Stability

• Warm fronts are more complex due to the stability of air masses.
• Unstable Air: Forced lifting leads to continuous rising, resulting in tall cloud formation (cumulonimbus) and thunderstorms.
• Conditionally Unstable Air: Becomes unstable upon condensation.
• Stable Air: Limited vertical movement, resulting in thinner cloud layers and less condensation.

Stability and Condensation

• Saturation vapor pressure decreases with temperature; cooler air supports more condensation.

Key Air Masses

• American Polar (MP)
• Continental Polar (CP)
• Maritime Tropical (MT)
• Continental Tropical (CT): Drier, warm air in the Southwest United States.

Front Steepness and Friction

• Cold fronts are steeper than warm fronts due to friction with the ground.
• Friction causes the cold air to burrow under warm air, leading to abrupt updrafts and potentially more extreme weather.
• Cold fronts can form rapidly due to their steepness.

Frontal Movement and Evolution

• Cold fronts often catch up to warm fronts.
• Density differences drive this behavior.

Frontogenesis

• Frontogenesis is the development and evolution of frontal boundaries.
• Typically involves a cold air mass to the north and a warm air mass to the south, separated by a stationary front.
• Wind shear (e.g., westerlies and easterlies) causes friction and distortion of the boundary.
• This distortion leads to counterclockwise motion, breaking the stationary front into a cold front and a warm front.
• Storm systems generally track from west to east due to prevailing westerlies and Hadley cell circulation.

Occluded Fronts

• Occur when a cold front catches up to a warm front.
• The warm air mass is lifted off the surface, resulting in the dissipation of fronts and temperature gradients.
• Represents the end of frontogenesis.
• The whole reason why weather exists is to equilibrate energy. Frontogenesis is weather trying to get rid of gradients and different energy levels.

Understanding Frontogenesis

• Understand that the collision of fronts marks the beginning of their end.
• The warm air mass is displaced aloft, eliminating the temperature gradient at the surface.
• Frontogenesis occurs due to temperature gradients between air masses.
• Fronts form at the borders between MP and MT air masses.
• The warm air that used to be at the surface is pushed aloft.

Weather Characteristics

• Different weather characteristics are associated with air masses and fronts.
• Extreme weather is associated with fronts.
• Hurricanes are not usually associated with fronts, and they are usually formed in the tropics where you don't have air masses of different characteristics, you got one of the air mass, and that MT air.
• Can get tornadoes in Hurricanes.
• Frontogenesis is associated with Thunderstorm, Tornadoes, precipitation, hail and extreme weather.

Thunderstorms

• Thunderstorms are rapid, effective events, updrafts. The updrafts are usually the result of unstable air where there's enough humidity in the air to get condensation, and the ability of the air gives you the energy to tall the cloud.
• Tall cloud stormy clouds, are called cumulonimbus clouds.
• Cumulonimbus clouds are the very, very tall clouds. They can extend to 6, 7, 8 miles up in the sky, 30,000, 40,000 feet in the sky. They grow very rapidly, and they're often times associated with strong precipitation, lightning.
• Because Thunderstorms oftentimes are associated with lightning, because almost always get lightning with the thunderstorm.

Lightning Strike Frequency

• Central Africa you have maximum curence.
• The United States The vast majority of lightning strikes is actually in the South East of the United States.
• What powers thunderstorm the sun?

Convective Thunderstorms

• Result of simply heating Earth's surface, like a sunny, hot day.
• Surface of the atmosphere. So that air warms up. As it warms up, it expands, becomes point start to rise.
• Can accelerate giving you a cumulonimbus cloud which is by definition thunderstorm.
• The onset of the convective activity can start at two, three, four in the afternoon, five, six in the afternoon.
• You have these very very strong updrafts, and those very strong updrafts are what holds condensed water in place.
• Rain falls, It cools the ground, and You are no longer able to heat overlying air, and so then that the storm dissipates.
• Also called the single cell thunderstorm. Typically, lasts, about just and an hour to two hours and then it's gone.

Hazardous Thunderstorm Characteristics

• Typically, starts to get windy when thunderstorm forms.

Airports Downdrafts

• An issue around airports, they called airport down, and that's why they close down the airport, don't want to have down drafts catch a plane.

Essential Thunderstorm Ingredients

• Heat, sunlight, relativity humid, and some sort of instability mechanism for uplift and production.

Types of Thunderstorms

• Because you can have thunderstorms at night as generated by fronts, you have force lifting. fact with fronts, more severe thunderstorms and single cell pop up thunderstorms of the type we were just talking.
• The area of most frequent thunderstorms is Florida.

Florida Thunderstorms

• Florida has most of the thunderstorms because it's being a piece of land sticking you out into the Atlantic, so have an air mass collision/convergence over this peninsula.
• Because the air replacing rising air, there's air coming in from both sides of Florida. That air in and of itself is going to want to rise as well. This is a area called air mass convergence as a result of lifting of that air.
• Florida is unique because been a peninsula was jutting out in big pools of water. On both sides of Florida, you have warm water, which then the air over that warm water rushes in all Florida as the warm air of Florida begins to rise as a result of solar.\
• Warm water, air rush in over Florida as warm air rises because of solar, which leads to the area promoting an updraft.

Severe Thunderstorms

• Hailstones, which are around an inch or bigger you have have to, and, or you have to have tornadoes you have to sustain surface winds around 60 miles an hour, 62 miles an hour, a hundred kilometers an hour.

Wind Shear and Mesocyclones

• Mesocyclone starts out actually on the ground, the horizontal rolling pin of air on the surface as a result of wind shear, because if I have wind going in this direction down below and if I have wind going in a direction aloft, will happens, start to and starts rotate.