Severe and Unusual Weather Test #3

What is a rain free base caused by?

updraft

What is highly unusual to have on the leading edge of a storm?

tornado

What is the most concerning part of a shelf cloud?

straightline winds

3 Body Scatter Spike

An artifact on a weather radar display indicative of large hail. They are identified by a spike of weak reflectivity echoes that extend out from a thunderstorm, and away from the radar site.

Tornado Basics

-50 to 275 knots wind speed
-150 ft to 1/2 mile path widths
-Most see 1-3 mile path lengths...strongest up to 30 mile path lengths
-Strength scale: weak...strong...violent
-Damage Scale (Enhanced Fujita Scale): EF0...EF1...EF2... EF3...EF4...EF5

Problems with the original Fujita Scale

-What about tornadoes in rural areas?
-All structures are not built the same
-Residential buildings vs commercial buildings?
-Building code compliance

Suction Vortices

Outgrowth of a very strong tornado

Tri State Tornado of 1925

-Worst tornado disaster in US history
-18 March 1925
-Track length: 179 miles
-Avg forward speed: 60-65 mph
-Avg path width in MO: 1/4 mile
-Avg path width in IL: 1/2 to 1 mile
-Killed: 695
-Injured: 2,027
-Damage: $16.5 million

Super Outbreak of Tornadoes

-3 and 4 April 1974
-Worst outbreak of tornadoes in US history
-148 tornadoes (At one time, 15 were on the ground simultaneously)
-Killed: 335
-Injured: 5,500
-Damage: $600 million

Landspouts

-Non-supercell (non-mesocyclone) thunderstorms often on frontal boundaries

Tropical Cyclone Related Tornadoes

Right forward side of tropical cyclone embedded within rainbands, difficult to see, very quick moving.

"Fair" Weather Waterspouts

Cumulus congestus cloud lines (not necessarily rain producing) weak short lived waterspouts

Supercell Waterspouts

Cumulonimbus clouds associated with supercells/ mesocyclones longer lived/ stronger tornadoes

Gustnadoes

Short lived and weak. Often on gust front/ outflow boundary. Circulation within boundary/ friction layer.

Cold Air Funnels

Develop from elevated convective clouds that develop over colder air. Often form under cumulus clouds in the circulation of large, upper air cut off lows. Rarely reach the ground.

Dust Devils

Associated with dry convection (hot surfaces)

Tornado Statistics

-"Tornado Alley" of the USA
-Only 25% of all tornadoes globally on avg are outside the US
-By geographical area
-Damage scale (Enhanced Fujita Scale)
-By month
-By hour
-By path length

Which month has the most tornadoes?

May

What month has more violent tornadoes?

April

Around what time do most tornadoes occur?

4-7 pm

Tornado Detection

-Storm spotters/ chasers
-WSR88D Doppler radar (velocity mode)
-Surface observations
- DOWs (Doppler on Wheels): University of Oklahoma, Texas A&M University

Storm Chasers vs Storm Spotters

Spotters know more about what they are doing and aren't just in it for a thrill...less liability.

Tornado Forecasting Tools

-Hourly surface analysis charts
-Constant height charts
-Thermodynamic diagrams
-Hodographs
-Computer models
-Composite charts
-SPC severe weather outlook/ guidance
-Atmospheric Stability Indices: CAPE, Lifted Index, Storm Relative Helicity, Energy Helicity Index

Composite Chart

Combines all weather elements and shows where they interact the most

5 Elements of a Thermodynamic Diagram

-Air Temp
-Temp Inversion
-Moisture
-Wind
-Instability

Where is most hail in regards to a tornado?

To the north and east of the tornado

4 Thunderstorm Ingredients

-Moisture
-Instability
-Lift
-Vertical wind shear

A severe storm has to have at least one of the following:

-Hail 1 in or larger in diameter
-Wind gusts at 58 mph or higher
-Tornado

5 Thunderstorm Types

-Single Cell
-Pulse
-Multicell Cluster
-Multicell Line
-Supercell

2 important characteristics that distinguish supercells from ordinary thunderstorms:

-Persistent rotation at the rain free base
-A rear flank downdraft

Types of Supercells

-Classic
-Low precipitation (LP)
-High precipitation (HP)

Lightening

-Forms as a result of separation of charges created because of the presence of ice crystals and cloud droplets in the strong updrafts and downdrafts.
-100 lightening strikes every second around the world
-On avg in the US, about 100 deaths and 1,000 injuries as a result of lightening
-On average in the US, $25 million in lightening damage every year
-Lightening can strike up to 10-20 miles away from the parent t-storm ("bolt from the blue")
-T-storms are officially observed when thunder is first heard and end 15 min after last thunder is heard

Where does lightening begin in t-storm development?

At the very end of the cumulus stage into the mature stage of t-storm development.

How big is a bolt of lightening?

About the diameter of a pencil

What is the temperature within a lightening bolt?

About five times the temperature of the outer surface of the sun.

Types of Lightening

-Cloud to ground (LTGCG)
-Cloud to cloud (LTGCC)
-Cloud to water (LTGCW)
-Cloud to air (LTGCA)
-Intracloud (LTGIC)
-...or combinations (LTGICCCCG)

Most frequent type of lightening

Cloud to cloud and Intracloud (60%)

Most deadly type of lightening

Cloud to Ground (20%)

Frequency of lightening

-Occasional (OCNL): less than one minute per flash
-Frequent (FQT): about 1-6 flashes per minute
-Continuous (CNS): More than 6 flashes per minute

Lightening "capital" of the US

Florida

Other lightening related terms

-Heat lightening
-Sheet lightening
-Ball lightening

Heat lightening

Seeing lightening, but not hearing thunder

Sheet lightening

can occur within a cloud, or intervening clouds, brightest part within a cloud

Ball lightening

looks like luminous sphere that appears to float in the air or slowly dart about for several seconds

Hail

-Hail size is entirely dependent of t-storms updraft and downdraft speeds
-When considering hail size, free fall velocity of hail stones is important when considering damage
-Mainly responsible for property and agricultural damage in the US; few injuries and deaths

What is considered severe hail?

1" diameter or larger

In regards to a tornado where does the largest hail often fall?

Northeast of the tornado

Where in the US is hail occurance most frequent?

In the central and southern plains

Largest hailstone in US history

7 inch in diameter and 18 3/4" in circumference in south central Nebraska at Aurora on June 22, 2003.

Straight Line Thunderstorm Winds

-Much more common than tornadoes
-Strong downdraft winds from thunderstorms
-Major threat to aviation
-Referred to, in general, as "downbursts"
-Wet and dry downbursts occur

Macroburst

Downburst "foot print" of greater than 2.5 miles in diameter

Microburst

Downburst "foot print" of 2.5 miles or less in diameter

Tornadoes

-A violently rotating column of air extending from the base of a cumulonimbus cloud and reaching the earths surface
-Narrow path with a convergent damage pattern

Flash Floods

-One of the top weather killers in the US
-General public does not understand the power of moving water

Types of flooding

Flash flooding and river flooding

Flash flood capital of the US

South central Texas

Why does south central Texas have so many flash floods?

-Subsoil limestone layers
-Urbanization
-Hilly nature of Texas hill country

What is the number one weather killer in the US?

Summer heat. Heat related illnesses and heat stroke