Overview: There are 5 lectures on Storms. 
The "roadmap" table below outlines what we cover each day.

Learning Goals (LG) are listed at the end of this web page.

Storms Day 4

• "Fractal", a video by Chad Cowan (stormlapse.com), is a wonderful "teaser" that you can watch before class starts.  It shows beautiful time-lapse images of mammatus clouds (which we will learn about today), mesocyclones, gust fronts, lightning, and other thunderstorms hazards. https://www.youtube.com/watch?v=kOlBirvzV5g  (3:22.  Not testable.)

• Here is a link to a pdf copy of the slides that I present in the video snippets today.  Some students use these pdfs for note taking and studying.
  

Mammatus

1. Mammatus clouds are sometimes seen on the underside of thunderstorm anvil clouds .  (1:40. Lecture Video snippet d4s01.)

2. To see beautiful time-lapse images of mammatus clouds, view only the one-minute segment between video timing marks 3:00 and 4:00 of the YouTube video called "Storm of Beauty" by Pecos Hank.  https://www.youtube.com/watch?v=0jkfnIBJRBQ  .
   

   • Check your understanding.  (d4c1)

Atmospheric Forces, Acceleration, and Wind

1. Newton's 2nd Law of Motion tells us how forces can cause objects to accelerate. When applied to the atmoshere, it allows us to forecast the winds.  (4:38. Lecture video snippet d4s03.)

• Check your understanding.  (d4c2)
  

2. But to forecast the winds, we need to know the forces that act on air parcels.  We will look at buoyancy forces in the vertical, which cause updrafts and downdrafts in storms. We will also look at pressure-gradient force in the horizontal, which can cause storm winds in horizontal directions.
   

Buoyancy Force causes Updrafts and Downdrafts

3. Temperature affects air density, and density differences affect buoyancy.  (2:34. Lecture video snippet d4s04.)

• Check your understanding.  (d4c3)
  

Pressure-Gradient Force drives Horizontal Winds

4. Pressure is force per unit area, and forces can cause motion. Thus, pressure gradients (pressure changes across horizontal distances) create forces that drive horizontal winds.  (4:41. Lecture video snippet d4s05.)

• Check your understanding.  (d4c4)
  

5. As shown using hurricanes as an example, horizontal changes in temperature cause horizontal pressure gradients that get stronger with increasing altitude. In hurricanes, this causes winds to flow outward at the top of the storm.
   

Continuity Links Vertical and Horizontal Winds in Circulations

6. Air molecules tend to distribute themselves approximately uniformly within any space -- a concept known as continuity.  (5:09. Lecture video snippet d4s06.)

• Check your understanding.  (d4c5)
  

7. Here is a slide summarizing how heat in the atmosphere can create motion.

Atmospheric Rivers

8. Atmospheric rivers caused extensive flooding in southern British Columbia during November 2021.  As the next images show, horizontal temperature variations associated with Lows (L) and Fronts create horizontal pressure gradients that drive moisture-laden winds called Atmospheric Rivers.  When the winds are forced to rise over mountain ranges, the rising air cools adiabatically, causing water vapour to condense to form precipitation. If the atmospheric river hits the same geographic location for many hours or days, then extreme precipitation can accumulate that causes flooding and landslides.

Hail

1. Pecos Hank has a wonderful YouTube video about hail. https://www.youtube.com/watch?v=6JbU0dIq70E  (7:00)
   

2. Hail risk and safety.  (3:43. Lecture video snippet d4s08.)
   

3. Here is a slide summarizing rain and hail hazards.
   

   • Check your understanding.  (d4c6)
     

Summary

1. Insights about how you can stay safe in storms.  (0:40. Lecture video snippet d4s09) 

2. The Learning Goals below are a good study aid for the topics we covered today.  Please review them now to reinforce your understanding.

By the end of this lesson, you should be able to: