The mesoscale convective system (MCS) index is an objective tool intended for use in forecasting MCSs. The MCS index indicates areas that are favorable for supporting MCS development and sustenance over the next six hours given that convective initiation has occurred or is expected to occur. The index is defined below:

 

where each term (i.e., lifted index (LI), 0-3 km shear, and 700 mb temperature advection) is normalized by subtracting the MCS sample mean and dividing by the sample standard deviation. Note that the MCS index should only be examined where convective development is probable (e.g., LI<0 chosen for these forecasts).

The MCS index is calculated using data from the North American Mesoscale (NAM) model analyses and forecasts.  Data from the GOES sounder (obtained from CIMSS) is also used to update values of the LI every hour, which is incorporated into analyses of the MCS index.  Additionally, GOES infrared data are overlaid on analyses of the MCS index to identify MCSs.

 

The table below provides general guidelines for the likelihood of MCS development given that a highly-concentrated group of thunderstorms has formed:

 

MCS index < -1.5 or undefined

unfavorable

-1.5 < MCS index < 0

marginal

0 < MCS index < 3

favorable

MCS index > 3

very favorable