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.

Description

Storm-relative helicity integrates the turning of winds relative to storm motion through a layer.

Storm-relative helicity integrates the turning of winds relative to storm motion through a layer. Its sign depends on the hodograph convention.^[1]

When to use Storm Relative Helicity SRH

Use this tool to 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.

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

How to use Storm Relative Helicity SRH and understand its results

Prepare the sounding profile or forecast verification counts. Check pressure levels, wind conventions, units and any requested layer bounds.
Enter heightsM, eastWindMPerSecond, northWindMPerSecond, stormMotionEastMPerSecond, stormMotionNorthMPerSecond, layerBottomM, layerTopM using the field table and calculation rules, then run the tool.
Read discreteStormRelativeHelicityM2PerSecond2. 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
heightsM	Heights m	list of number	Required
eastWindMPerSecond	East wind m per second	list of number	Required
northWindMPerSecond	North wind m per second	list of number	Required
stormMotionEastMPerSecond	Storm motion east m per second	number	Required
stormMotionNorthMPerSecond	Storm motion north m per second	number	Required
layerBottomM	Layer bottom m	number	Required
layerTopM	Layer top m	number	Required

Use increasing heights and aligned east/north winds with ordered layer bounds inside observed coverage. Interpolate boundary winds and sum oriented segment products. Return signed m²/s², with conventional clockwise turning positive.^[2]

SRH = Σ (upper east−storm east)(lower north−storm north) − (lower east−storm east)(upper north−storm north)

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

Output field	Meaning	Value type
discreteStormRelativeHelicityM2PerSecond2	Discrete storm relative helicity m2 per second2	number

json

{
  "input": {
    "heightsM": [
      0,
      1000
    ],
    "eastWindMPerSecond": [
      0,
      10
    ],
    "northWindMPerSecond": [
      10,
      0
    ],
    "stormMotionEastMPerSecond": 0,
    "stormMotionNorthMPerSecond": 0,
    "layerBottomM": 0,
    "layerTopM": 1000
  },
  "output": {
    "discreteStormRelativeHelicityM2PerSecond2": 100
  }
}

Limitations and assumptions

Storm motion is supplied; no tornado probability or extrapolated layer winds are inferred.

Numbers and computed results must be finite; overflow produces an error. Numeric lists are limited to 100,000 entries; the rules above may require smaller limits. Missing required fields, extra fields, wrong value types and violations of the calculation rules are input errors.

Alternative or Complementary methods

Use 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. For a complementary task, use Trade Wind Inversion Base Height Lookup: Identify measured contiguous inversion layers at caller lapse threshold and report observed base/top brackets; no climatological trade-wind lookup or inference of inversion between unresolved samples.

Further background: Convective environmental parameters and indices.

References

Convective environmental parameters and indices — National Weather Service
Storm Relative Helicity SRH — tool.io

Similar or alternative tools

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.
Trade Wind Inversion Base Height Lookup
Identify measured contiguous inversion layers at caller lapse threshold and report observed base/top brackets; no climatological trade-wind lookup or inference of inversion between unresolved samples.