The TT (Total Totals) is an index used to assess storm strength. The TT is a combination of the Vertical Totals (VT) and Cross Totals (CT). The VT is the temperature difference between 850 and 500 mb while the CT is 850 mb dewpoint minus the 500 mb temperature.
TT = (T850 - T500) + (Td850 - T500)
| <44 |
Convection not likely |
| 44-50 |
Likely thunderstorms |
| 51-52 |
Isolated severe storms |
| 53-56 |
Widely scattered severe |
| >56 |
Scattered severe storms |