AHS 106 Day 23: Severe Weather and Tornadoes Study Notes

Class Business

  • Group Sheets: Each group needs one group sheet.

  • Individual Sheets: An individual sheet is required for every participant.

  • SmartBook Assignments:

    • SmartBook 12 on Hurricanes is due on November 20.

    • SmartBook 13 on Wildfires is due on November 25.

  • Final Exam Schedule: Scheduled for December 11 from 2:45 PM to 5:15 PM.

  • Today's Topics:

    • Hail

    • Supercells

    • Tornadoes

    • Tornado Safety

Hail

  • Definition of Hail: Hail consists of balls of ice that form within thunderstorms.

    • Notable personality related to hail: George Kourounis.

Hail Formation and Characteristics

  • Riming:

    • Defined as the accumulation of large amounts of super-cooled water found in the upper levels of a cloud.

    • Super-cooled water: Water that exists in a liquid state below its freezing point.

    • Can freeze onto various surfaces, including:

    • Branches

    • Airplanes

    • Existing ice crystals

  • Riming on Snowflakes:

    • Riming can also occur on snowflakes, leading to the formation of ice pellets, known as graupel.

    • Visual aids:

    • Unrimmed snowflake vs. rimed snowflake.

Hail Size

  • Hail sizes can be compared using a chart that includes various common objects.

  • Hail Size Comparison Examples:

    • Softball: 3.8 inches

    • Golf Ball: 1.75 inches

    • Baseball: 2.75 inches

  • Sizing visual comparison is important for reports and forecasts.

Historical Context of Hail

  • Notable Hailstone:

    • The largest recorded hailstone in the U.S. fell in Vivian, SD in 2010, measuring 8 inches in diameter and weighing nearly 2 pounds.

Hail's Economic Impact

  • Crop Damage: Hail can destroy crops, leading to economic losses of around $1 billion per year.

  • Structural Damage: Hail also causes significant damage to buildings and vehicles.

Hail Safety

  • Safety Recommendations:

    • The most critical advice during a hailstorm is to GET INSIDE and STAY INSIDE!

    • Advisories on inappropriate methods to protect vehicles during hailstorms are discussed humorously.

Supercells

Characteristics of Supercells

  • Definition: Supercells are long-lasting thunderstorms, often persisting for several hours.

  • Key Features of Supercells:

    • Rotating updraft

    • Need for directional wind shear.

    • Wind speeds can reach up to 100 mph.

Wind Shear in Supercells

  • Directional Wind Shear: Supercells favor winds that turn clockwise with altitude, including:

    • Southeasterly winds

    • Westerly winds

    • Southerly winds

    • Southwesterly winds

  • Mechanism: Shear creates rotational movement around a horizontal axis and influences the storm's dynamics.

Updraft Mechanics

  • As the updraft tilts, it influences the vortex tube rotation, primarily counterclockwise.

  • Observation in Structure:

    • The structure of the supercell reveals rotation that often leads to tornado formation.

Supercell Videos

  • Viewing multiple videos of supercells emphasizes observable rotation within these storms.

Tornadoes

Definition of Tornadoes

  • A tornado is defined as a rapidly rotating column of air (vortex) that extends downward from a thunderstorm.

  • Notable Example: Drone video showcasing a tornado in Andover, KS (2022).

Tornado Formation in Supercells

  • As surface air converges with the supercell's updraft, the rotation rate intensifies—similar to an ice skater performing a pirouette.

Characteristics of Tornadoes

  • Tornadoes possess distinct features, including:

    • Mesocyclone

    • Wall cloud

    • Funnel cloud

    • Debris cloud

Radar Signature of Tornadoes

  • Hook Echo: A signature indicating the presence of a tornado, marked by rain wrapping around the mesocyclone.

    • Recognition of the hook echo in radar data is crucial for predicting tornado occurrences.

Tornado Damage Ratings

  • Fujita Scale: Developed by Dr. Theodore Fujita, it categorizes tornado intensity based on post-storm damage assessments.

  • Enhanced Fujita Scale (EF-scale): This updated scale measures tornado intensity using damage estimates without relying solely on observed wind speeds.

EF Rating Breakdown

  • Intensity Ratings and Associated Wind Speeds:

    • EF-0: 65-85 mph (Minor damage)

    • EF-1: 86-110 mph (Moderate damage)

    • EF-2: 111-135 mph (Considerable damage)

    • EF-3: 136-165 mph (Severe damage)

    • EF-4: 166-200 mph (Extreme damage)

    • EF-5: > 200 mph (Massive/incredible damage)

  • Damage Descriptions: Examples of the types of structures affected and the expected damage associated with each rating.

Tornado Cases and Historical Context

Case Study: Sauk Rapids, MN, 1886

  • Date: April 14, 1886

    • Sauk Rapids was a significant city in Minnesota at that time, with the tornado rated as F4.

    • Fatalities: 44 in Sauk Rapids, contributing to a total of 72 deaths due to flying debris.

Case Study: Greensburg, KS, 2007

  • The tornado reached about ¾ of a mile wide, causing major destruction.

  • Fatalities: Eleven people died.

Case Study: Joplin, MO, 2011

  • This EF-5 tornado resulted in 161 total deaths, marking a significant historical event as the deadliest U.S. tornado in 60 years.

  • Economic Losses: Estimated damage was around $2.2 billion.

  • Destruction Extent: Approximately 10%-20% of the town was destroyed; ~75% of the town was damaged.

Case Study: Rochelle-Fairdale, IL, 2015

  • An EF-4 tornado that lasted for 41 minutes covering a distance of 30 miles.

Tornado Safety and Preparedness

Alerts and Warnings

  • Watches vs. Warnings:

    • Watch: Conditions are favorable for severe weather; stay updated.

    • Warning: Weather event is present and immediate action for shelter is necessary.

Tornado Safety Rules

  • Best Place During a Tornado: Get as far away from the tornado path as possible if safe to do so.

  • In your Home Safety:

    • Generally safe in sturdier homes during lower-rated tornadoes (EF0 or EF1).

    • Mobile homes are not considered safe during any tornado event.

Seeking Shelter

  • The best protection during a tornado includes:

    • Underground shelters

    • Basements or dedicated “safe rooms”

    • Stay away from windows and cover under sturdy objects.

Mobile Home Risks

  • Historical data identifies that mobile homes account for a significant number of tornado fatalities often due to their vulnerability to heavy winds.

Best Practices while in a Car

  • Driving to Safety: If possible, drive away from the tornado.

  • If Trapped: Find a ditch or shelter, but avoid hiding under overpasses as this poses severe risks.

Visual Aids and Reportings

  • Various photographs and visual aids have been used to document and communicate the impacts and protocols for tornado safety scheduling.