1. Locating (and Forecasting) Thunderstorms on Weather Maps METR 180 (Lightning and Thunderstorms)

2. We have seen how unstable humid air can lead to thunderstorms. Can we do better? For example, what areas will see thunderstorms? Even better, can we figure out which ones will get very strong thunderstorms, like this one?

3. Here’s a day that looks fairly active. All the dots were not just thunderstorms, but very strong thunderstorms. They had high winds, and hail. Most of the strong wind (blue dots) are in Michigan.

4. Lower Peninsula Here’s a map of the state of Michigan. The part south of the “pinch” is called the Lower Peninsula. Detroit Upper Peninsula

5. Radar showed numerous heavy thunderstorms the morning of April 25, 2009

6. The Lower Peninsula of Michigan was particularly hard-hit

7. What’s happening in Michigan? (see next slide)

8. Here are the local winds in Michigan and vicinity (a little later). In meteorology, the flags go in the direction of the wind, like arrows. This is the symbol for a thunderstorm

9. For instability, you need cold air aloft.

10. Same map, just a closer view -16  C is cold at 500 mb

11. What is on this map?

12. It’s the edge of the jet stream. The triangles mean 55 mph wind. This is 143 mph! It’s 72 mph in the Lower Peninsula

13. The atmosphere must have one more feature to produce heavy thunderstorms on April 25, 2009. What haven’t we discussed? It’s LIFT! We haven’t seen the surface map yet. Something pushed the parcels up. In other words, it gave the air a boost to rise from the surface.

14. e.

15. Fronts Cold frontWarm front Both cold and warm fronts produce lift. The lift with a cold front is usually stronger and is more likely to form thunderstorms but warm fronts do it too.

16. The colors show the temperatures. Where is the front?

17. Surface map on April 25. Lift is definitely in order.

18. Satellite Loop.

19. Terrain effects – also known as orographic uplift. This wasn’t happening in Michigan (maybe it would have happened in the upper peninsula which is mountainous)

20. Extreme Heating at the Earth’s surface When it gets really hot at the ground, air rises spontaneously. In deserts, this causes dust devils. This definitely did not occur that day in Michigan. Where there is more humidity, clouds and storms form.

21. Just for fun

22. So, are we ready to find areas that will get thunderstorms? This will be the basis of exercise 2, to be done Thursday. Questions?