Introduction

This page describes two studies of different convective cases; one over N. America associated with formation of severe tornadoes, the other over central Africa.

Both cases are studied starting the forecast from the same date/time (initial conditions).

The N.America case has strong large scale forcing whereas the central African case is driven by the diurnal cycle.

US Tornado convection case (Arkansas)

On the 27 April 7pm local time (00UTC 28 April), tornadoes hit towns north and west of Little Rock, Arkansas killing approx 17 people.  (http://edition.cnn.com/2014/04/28/us/severe-weather/index.html?hpt=hp_c2). On the evening on the 28 April fatal tornadoes occurred over Mississippi (http://www.bbc.co.uk/news/world-us-canada-27199071).

More information can also be found on the ECMWF Severe Event Catalogue 201404 - Convection - Arkansas U.S.

African diurnal deep convection (Central Africa)

To be done.

 

 

Initial conditions

To be done.

Key questions to address with the control forecast

TODO: Add maps.

Case study: N.America deep convection

On 27 April 2014 7pm local time (00UTC 28 April), tornadoes hit towns north and west of Little Rock, Arkansas.


  1. Understand the weather situation resulting in tornadoes
  2. Evaluate the control forecast and compare it to the ECMWF reanalysis and observations
  3. What is the area of threat according to the control forecast? TODO: explain
  4. How does the convective adjustment process takes place and and what is the role of large scale forcing (why and where it happens)?

 

Case study: African deep convection

TODO: note area of interest (show WV image?)

 

  1. Understand the weather situation over Africa.
  2. What is the role of large scale in this case (compare with N.America case).
  3. Look at the diurnal variation of key parameters (2m temperature, surface heat fluxes, precipitation, outgoing-longwave-radiation) for location 0N,25E.
  4. Compare differences in convection profiles between Central Africa and (i) open ocean, and (ii) Amazonia.

Sensitivity experiments

The IFS is highly tuned to give the best forecast over a range of initial conditions. However, it is instructive to try some sensitivity experiments to understand the role of various physical and dynamical processes.

Not all of the suggested experiments are applicable to both cases, indicated in brackets.


Additional questions

Further reading

More information about the N.American tornadoes can be found on the ECMWF Severe Event Catalogue - 201404 - Convection - Arkansas U.S

Comments

The forecasting system at ECMWF makes use of "ensembles" of forecasts to account for errors in the initial state. In reality, the forecast depends on the initial state in a much more complex way than just the model resolution or starting date.  At ECMWF many initial states are created for the same starting time by use of "singular vectors" and "ensemble data assimilation" techniques which change the vertical structure of the initial perturbations.

As further reading and an extension of this case study, research how these methods work.

Acknowledgements

 

 

 

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