What is SWEAT?
SWEAT meaning Severe Weather ThrEAT index; a stability index developed by the Air Force which incorporates instability, wind shear, and wind speeds as follows:
SWEAT=(12 Td 850 ) + (20 [TT-49]) +( 2 f 850) + f 500 + (125 [s+0.2]) where
- Td 850 is the dew point temperature at 850 mb,
- TT is the total-totals index,
- f 850 is the 850-mb wind speed (in knots),
- f 500 is the 500-mb wind speed (in knots), and
- s is the sine of the angle between the wind directions at 500 mb and 850 mb (thus representing the directional shear in this layer).
SWEAT values of about 250-300 or more indicate a greater potential for severe weather, but as with all stability indices, there are no magic numbers.
The SWEAT index has the advantage (and disadvantage) of using only mandatory-level data (i.e., 500 mb and 850 mb), but has fallen into relative disuse with the advent of more detailed upper air sounding analysis programs.
reference: National Weather Service Glossary