Turbulence

This 3-D field shows expected turbulence levels on a 0-1 scale as predicted by ITFA - the NCAR Integrated Turbulence Forecasting Algorithm. The colors indicate the turbulence level or intensity (smooth, light, moderate, severe). ITFA is only computed on the high-resolution domains of the WRF model. For that reason the Turbulence product only covers domain 2 and domain 3, but does not extend to domain 1. The specific ITFA threshold values for each intensity category are:

Smooth	ITFA < 0.25
Light	0.25 < ITFA < 0.50
Moderate	0.50 < ITFA < 0.75
Severe	ITFA > 0.75

Various researchers have derived indices aimed at predicting the presence of turbulence from numerical weather prediction model (such as WRF) data. The AOAWS ITFA computes the following 8 of these indices:

1. Ellrod1 (shear x deformation)
2. NGM1 (speed x deformation)
3. DTF3 (turbulence kinetic energy)
4. -Ri (stability/wind shear)
5. TEMPG (magnitude of horizontal temperature gradient)
6. -NVA (negative vorticity advection)
7. NCSU1 (advection x vorticity gradient/Ri)
8. EDR (eddy dissipation rate)

The combination of indices at any given point is calculated as follows:

1. A weight W_i is assigned to each index i, based on its relative performance deduced from comparisons to PIREPs over the U. S.
2. Each index D_i is computed from the WRF output.
3. Each index is normalized to 0-1, D*_i.
4. The ITFA weighted sum of indices is computed as
   ITFA = Sum(W_i D*_i) / Sum( W_i)

The current weights Wi for each of the 8 indices are as follows

Index	Weight
ELLROD1	0.656
NGM1	0.502
DTF3	0.534
RI	0.545
TEMPG	0.629
-NVA	0.537
NCSU1	0.606
EDR	0.575

Turbulence All-levels