Mesoscale convective systems occur worldwide and year-round and are accompanied by the potential for severe weather and flooding. This lesson describes typical system evolution by examining squall line, bow echo, and MCC characteristics throughout their life cycles. This lesson has less emphasis on the physical processes controlling MCS structure and evolution than our previously released Mesoscale Convective Systems: Squall Lines and Bow Echoes lesson. Instead, this newly updated lesson includes more material on tropical squall lines, MCC's, and on NWP’s ability to predict convective systems. The lesson starts with a forecast scenario and concludes with a final exam. Rich graphics, audio narration, and frequent interactions enhance the learning experience.
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After completing this lesson, you should be able to do the following things.
- Recall the definition of an MCS
- Recall common types of MCS organization, especially squall lines and bow echoes
- List the potential weather hazards most likely associated with MCSs
- Identify key features associated with MCS initiation and evolution
- Recognize a likely MCS in radar imagery Squall Lines
- Identify the various forms and compositions of squall lines
- Locate key squall line structures, including the cold pool, leading gust front, and rear-inflow jet
- Recall evolution of the surface pressure pattern during the lifetime of a squall line
- Explain the types of squall line formation
- Identify the phases of squall line evolution
- Using satellite and radar imagery, recognize the type and phase of a squall line
- Explain what determines if a squall line will be weak-to-moderate or moderate-to-strong
- Quantify low-level shear and identify which vertical wind shear most controls squall line strength
- Recall movement of long lines versus short lines, and movement of cells within a line
- Identify line back building and recognize conditions which support it
- Describe a line echo wave pattern and identify one from radar data
- List the differences between tropical and extratropical squall lines Bow Echoes
- Define bow echoes and identify weather patterns conducive to their development
- Explain what a rear-inflow notch is and how to assess it with the MARC technique
- Discuss the factors that contribute to bow echoes being an especially severe form of MCS
- Describe the most likely time of onset and location of damaging winds from a bow echo
- Describe the characteristics of a derecho Mesoscale Convective Complexes (MCCs)
- Recall how MCCs are defined via satellite imagery
- Describe where MCCs usually occur
- List the potential weather hazards associated with MCCs
- Explain what an MCV (or MVC) is and its relationship to an MCC
- Recognize the signature of an MCV from satellite imagery
- Recall why it is important to monitor an MCV MCSs and Numerical Weather Prediction (NWP)
- List model convection issues and describe their impact on forecast elements
- Describe the difference between a model with convective parameterization and one without
- List the relative strengths and weaknesses of using a model with higher resolution (10 km WRF) versus one with lower resolution (22 km Eta)
- Describe common NWP limitations and errors related to forecasting large-scale convection
- Explain how model output should be applied to forecasting MCS occurrence
MCS, severe convection, mesoscale convective systems, squall line, convection, MCS organization, MCS structure, MCS evolution, bow echo, bow echoes, gust front, cold pool, derecho, rear-inflow jet, RIJ, mid-altitude radial convergence, MARC, back building, back-building, line echo wave pattern, LEWP, tropical squall line, MCV, MVC, Mesoscale Convective Vortex, MCC, mesoscale convective complex, NWP, numerical weather prediction, convective parameterization
September 2016: This lesson has been updated to conform to current HTML standards and brings the original content to a new, easier to navigate format. The title was changed, dropping the numeral from Severe Convection II.
July 2014: Due to its age, this lesson contains products generated from the Eta model, which is no longer in operational use. This primarily impacts the MCSs and NWP section. Additionally, while the information presented is largely still valid, it does not include new discoveries including MCSs initiated as elevated convection, not surface convection. Much of this work is covered in literature by Schumacher.
