| NATS 101 Lecture 27 Thunderstorms |
| Thunderstorm Basics |
| What is a thunderstorm? | |
| A cumulonimbus with lightning and thunder! | |
| Several km deep layer of conditionally unstable air is necessary to produce a cumulonimbus. Unstable layer lasts until: | |
| -Parcels rise far enough to condense into clouds. | |
| -Once the cloud topped thermals penetrate into the conditionally unstable layer, thunderstorms rapidly develop and the instability is released. |
| Annual Average Days with Thunderstorms |
| Types of Thunderstorms |
| Single Cell | |
| Multicell | |
| Squall Line | |
| Mesoscale Convective Complex | |
| Supercell (Tornado Lecture - Later) |
| Life Cycle of Air-Mass Thunderstorm |
| Mature Air-Mass Thunderstorm |
| Dissipating Thunderstorm |
| Severe Thunderstorm |
| A severe thunderstorm is a thunderstorm having at least one of the following: | |
| -Hail with diameter of 3/4Ó or greater | |
| -Winds of 50 knots (57 mph) or faster | |
| -Tornado |
| Severe Thunderstorm Features |
| Severe Thunderstorm Features |
| Overshooting Top |
| Shelf Cloud or Arcus Cloud |
| Roll Cloud |
| Severe Thunderstorm Weather |
| Sounding for Severe T-storm |
| Parcel is more than 10oC warmer than the ambient air from 500-200 mb! | |
| Sounding can give updraft speeds of nearly 100 mph! |
| Multicell Thunderstorm |
| Squall Line Formation |
| Squall Line Structure |
| Squall line propagation across the upper midwest |
| Old Storms Initiate New Storms |
| Phoenix Storm July 14, 2002 |
| Hazards from Thunderstorms |
| Lightning (Next Lecture) | |
| Hail | |
| Microburst Winds | |
| Flash Flooding | |
| Tornadoes (Lecture after Lightning) |
| Hail |
| Hail forms when ice particles are repetitively circulated inside T-storm. | |
| Diameter of hail indicates strength of updraft speed. | |
| 3Ó hail-100 mph updraft | |
| Hail is a serious economic threat to agriculture and a major public hazard. |
| Annual Average Days with Hail |
| Microbursts |
| Dry - Wet Microbursts | |
| Evaporation of rainfall cools air below cloud. | |
| The heavier, cooled air accelerates downward. | |
| Falling rain accentuates downward acceleration. | |
| Rapidly sinking air hits the ground and fans out as annulus of high winds. | |
| Common in AZ Summer |
| Dry Microburst |
| Wet Microburst |
| Microbursts and Wind Shear |
| Aviation Risks | |
| Microbursts are a serious hazard to aviation | |
| Rapid change in winds can lead to loss of lift during take-off, landing | |
| Microbursts have caused several crashes of jets |
| Mesoscale Convective Complexes |
| State-sized area of thick raining anvil that forms from organized storms. | |
| Located south of jet axis. | |
| Form during evening and last all night. | |
| Rainfalls of 2Ó-5Ó common Flash flooding hazard | |
| MCCÕs produce half of Midwest summer rains. |
| Heavy Flash Flooding |
| Do Not Enter Arroyos! |
| Monsoon rains, many miles away, can cause arroyos to rise several feet in a few seconds. | |
| Some cars can begin to flow when water depth exceeds just 6Ó- 8Ó. | |
| DonÕt risk being a... | |
| ÒStupid MotoristÓ or... | |
| ÒDarwin WinnerÓ |
| Supercell Thunderstorms |
| Summary: Key Concepts |
| What is a thunderstorm? | |
| A cumulonimbus with lightning and thunder! | |
| Deep layer of conditionally unstable air is necessary to produce a cumulonimbus. | |
| Several types of thunderstorms. | |
| Can pose serious hazards to public safety, transportation and commerce sectors. |
| Assignment for Next Lecture |
| Topic - Lightning and Thunder | |
| Reading - Ahrens pg 267-273 | |
| Problems - 10.15, 10.16, 10.17, 10.18 |