Based on the calculation in the url we could extend
val T = temperature.state as Number
val RH = humidity.state as Number
val HI = -42.379 + 2.04901523*T + 10.14333127*RH - .22475541*T*RH - .00683783*T*T - .05481717*RH*RH + .00122874*T*T*RH + .00085282*T*RH*RH - .00000199*T*T*RH*RH
if (RH< 13 && T>= 80 && T<=110) {
// ADJUSTMENT = [(13-RH)/4]*SQRT{[17-ABS(T-95.)]/17}
var adjust = ((13-RH)/4) * Math.sqrt(17-Math.abs(T-95.)/17)
HI -= adjust
} else if (RH>85 && T>80 && T<87) {
// ADJUSTMENT = [(RH-85)/10] * [(87-T)/5]
var adjust = ((RH-85)/10) * ((87-T)/5)
HI += adjust
} else if (T<80){
// HI = 0.5 * {T + 61.0 + [(T-68.0)*1.2] + (RH*0.094)}
HI = 0.5 * (T + 61.0 + ((T-68.0)*1.2) + (RH*0.094))
}
// remember it is in F in Germany you would prefer to use C
// C to F = T(°F) = T(°C) × 9/5 + 32
// F to C = T(°C) = (T(°F) - 32) × 5/9