1. Bellwork 5/11 Happy Friday!! 
Using the surface map and the data provided, describe why our current weather is occurring. (Today is tricky!!)

2. Coming Up Today: Finish severe weather, work time
Tuesday 5/15: Work day
MAKE SURE YOU HAVE DATA FOR THIS DAY!
Thursday 5/17: Weather Project due, Begin climate unit

3. We’ve entered Severe Weather Season in the US!
First WI Tornado in Washington County

4. Severe weather types Thunderstorms Occurrence Features
2,000 in progress at any one time
Cumulonimbus clouds
Heavy rainfall, hail
100,000 per year in the United States
Lightning
Most frequent in Florida and eastern Gulf Coast region
Live Data

5. Average number of days per year with thunderstorms

6. Worldwide Thunderstorm Activity

7. Thunderstorms All thunderstorms require Warm, moist air
Instability (lifting)
High surface temperatures
Most common in the afternoon and early evening

8. Thunderstorms—Stages of Development
1. Cumulus stage
Require continuous supply of warm air and moisture
Updrafts start to form
“stocking up” on precipitation depending on the strength of the updraft

9. Thunderstorms 2. Mature Stage: 3.Dissipating Stage
Eventually heavy precipitation falls
Gusty winds, lightning, hail
3.Dissipating Stage
Warm surface temperatures are gone, ending the updrafts
Precipitation becomes light
Cooling effect of precipitation triggers the end of thunderstorm activity

10. Lightning How does it form? Water droplets freeze from the outside in.
Water expands as it freezes, causing the icy shell to shatter—lighter ice pieces are pushed upward and heavier water/ice particles fall toward the bottom
Friction between these particles causes electrons to be “ripped off”
The top of the cloud is then concentrated with positive charges, while the bottom of the cloud is negatively charged.
Lightning

11. How does a lightning bolt form?
When the differences in charge have built up enough, the negative charge “looks” for a place to release its charge.
Takes the path of least resistance
Most lightning occurs within or between clouds. Some occurs between a cloud and the ground

13. Thunder Heat from lightening causes the air around it to warm rapidly
This warm air expands and then quickly cools and contracts
This contraction causes the noise we hear after a lightning strike.
Speed of sound: ~340m/s
Speed of light: 299,792,458 m/s

14. Severe weather types Tornadoes Local storm of short duration Features
Rotating column of air that extends down from a cumulonimbus cloud
Low pressures inside causes the air to rush into the center

15. Tornadoes Occurrence and development
Most frequent from April through June
Exact mechanism of tornadoes formation is not known
Basic observations show us:
1. Strong winds create horizontal rotation
2. Updrafts (associated with thunderstorm) force the rotation in a vertical position
3. Mesocyclone created & MIGHT touch down on the ground

17. Only about HALF of the mesocyclones formed become tornadoes!

18. Conditions for the formation of tornadoes
Occur most often along a cold front
Associated with huge thunderstorms called supercells
Cold cP air mixing with warm mT air
Larger the difference, larger the storm

21. How do we track a tornado?
Doppler Radar
VORTEX2 projects
TOTO…(didn’t work)…Twister instrument was modeled after this

22. Measuring a Tornado Can only be measured AFTER a tornado has passed
Intensity measured by the Enhanced Fujita intensity scale
Can only be measured AFTER a tornado has passed

23. Severe weather types Tornadoes Tornado forecasting
Difficult to forecast because of their small size
Tornado watch
To alert the public to the possibility of tornadoes
Issued when the conditions are favorable
Covers 65,000 square km (25,000 square miles)

24. Severe weather types
Tornado warning is issued when a tornado is sighted or is indicated by weather radar
Use of Doppler radar helps increase the accuracy by detecting the air motion

25. Work time Hurricane Lab Weather project
Make sure you have all of your data collected
Start organizing/analyzing the data you do have!