SWEAT Index Severe

Evaluate named SWEAT with dewpoint/total-totals truncation and conventional direction/speed gates on shear term, explicit knots/wind-from degrees; not a calibrated warning or severe-weather probability.

Description

SWEAT combines moisture, thermal instability and wind terms.

SWEAT combines moisture, thermal instability and wind terms. Its directional shear contribution is enabled only under specific sounding gates.^[1]

When to use SWEAT Index Severe

Use this tool to evaluate named SWEAT with dewpoint/total-totals truncation and conventional direction/speed gates on shear term, explicit knots/wind-from degrees; not a calibrated warning or severe-weather probability.

Prepare the sounding profile or forecast verification counts. Check pressure levels, wind conventions, units and any requested layer bounds.

How to use SWEAT Index Severe and understand its results

Prepare the sounding profile or forecast verification counts. Check pressure levels, wind conventions, units and any requested layer bounds.
Enter temperature850C, temperature500C, dewpoint850C, wind850Knots, wind500Knots, wind850FromDegrees, wind500FromDegrees using the field table and calculation rules, then run the tool.
Read sweatIndex, directionalShearTerm. The explanation below defines the units, signs, ordering and any flags or placeholder values.
If the tool reports an input issue, correct the values and run it again. Apply the stated assumptions when interpreting a successfully returned result.

Input field	Meaning	Value type; see rules below	Requirement
temperature850C	Temperature850 c	number	Required
temperature500C	Temperature500 c	number	Required
dewpoint850C	Dewpoint850 c	number	Required
wind850Knots	Wind850 knots	number	Required
wind500Knots	Wind500 knots	number	Required
wind850FromDegrees	Wind850 from degrees	number	Required
wind500FromDegrees	Wind500 from degrees	number	Required

Use Celsius, nonnegative knots and wind-from degrees in [0,360), with dewpoint no greater than the 850-hPa temperature. Compute Total Totals as TT = temperature850C + dewpoint850C − 2 × temperature500C. Shear is 125(sin(direction500−direction850)+0.2) only for 850-hPa wind direction in [130°,250°], 500-hPa wind direction in [210°,310°], increasing direction and both speeds at least 15 knots; otherwise zero.^[2]

SWEAT = 12max(0,Td850) + 20max(0,TT−49) + 2wind850 + wind500 + gated shear

Units, indexing, boundary conditions and exceptional cases are defined in the calculation rules above.

Output field	Meaning	Value type
sweatIndex	Sweat index	number
directionalShearTerm	Directional shear term	number

json

{
  "input": {
    "temperature850C": 20,
    "temperature500C": -10,
    "dewpoint850C": 10,
    "wind850Knots": 20,
    "wind500Knots": 20,
    "wind850FromDegrees": 180,
    "wind500FromDegrees": 270
  },
  "output": {
    "sweatIndex": 350,
    "directionalShearTerm": 150
  }
}

Limitations and assumptions

The index is not severe-weather probability or a warning threshold.

Numbers and computed results must be finite; overflow produces an error. Missing required fields, extra fields, wrong value types and violations of the calculation rules are input errors.

Alternative or Complementary methods

Use Total Totals Index: Resolve named vertical/cross/total totals from fixed 850/500-hPa observations; unlike K index, no 700-hPa moisture layer and no storm occurrence/safety classification. For a complementary task, use Storm Relative Helicity SRH: Integrate signed storm-relative hodograph helicity over bounded observed layer using piecewise-linear winds and supplied storm motion; clockwise turns use positive conventional SRH, not tornado probability.

Further background: Convective environmental parameters and indices.

References

Convective environmental parameters and indices — National Weather Service
SWEAT Index Severe — tool.io

Similar or alternative tools

Total Totals Index
Resolve named vertical/cross/total totals from fixed 850/500-hPa observations; unlike K index, no 700-hPa moisture layer and no storm occurrence/safety classification.
Storm Relative Helicity SRH
Integrate signed storm-relative hodograph helicity over bounded observed layer using piecewise-linear winds and supplied storm motion; clockwise turns use positive conventional SRH, not tornado probability.