(temp, humidity, dew=None)
return ((c_1 + (c_2 * T) + (c_3 * R) + (c_4 * T * R) + (c_5 * (T**2)) +
             (c_6 * (R**2)) + (c_7 * (T**2) * R) + (c_8 * T * (R**2)) +
             (c_9 * (T**2) * (R**2))) - 32.0) / 1.8
Calculate Heat Index as per USA National Weather Service Standards

    See http://en.wikipedia.org/wiki/Heat_index, formula 1. The
    formula is not valid for T < 26.7C, Dew Point < 12C, or RH < 40%
Calculate Heat Index as per USA National Weather Service Standards
Calculate Heat Index as per USA National Weather Service Standards
def usaheatindex(temp, humidity, dew=None):
    """Calculate Heat Index as per USA National Weather Service Standards

    See http://en.wikipedia.org/wiki/Heat_index, formula 1. The
    formula is not valid for T < 26.7C, Dew Point < 12C, or RH < 40%

    """
    if temp is None or humidity is None:
        return None
    if dew is None:
        dew = dew_point(temp, humidity)
    if temp < 26.7 or humidity < 40 or dew < 12.0:
        return temp
    T = (temp * 1.8) + 32.0
    R = humidity
    c_1 = -42.379
    c_2 = 2.04901523
    c_3 = 10.14333127
    c_4 = -0.22475541
    c_5 = -0.00683783
    c_6 = -0.05481717
    c_7 = 0.00122874
    c_8 = 0.00085282
    c_9 = -0.00000199
    return ((c_1 + (c_2 * T) + (c_3 * R) + (c_4 * T * R) + (c_5 * (T**2)) +
             (c_6 * (R**2)) + (c_7 * (T**2) * R) + (c_8 * T * (R**2)) +
             (c_9 * (T**2) * (R**2))) - 32.0) / 1.8
def usaheatindex ( temp , humidity , dew = None ) : if temp is None or humidity is None : return None if dew is None : dew = dew_point ( temp , humidity ) if temp < 26.7 or humidity < 40 or dew < 12.0 : return temp T = ( temp * 1.8 ) + 32.0 R = humidity c_1 = - 42.379 c_2 = 2.04901523 c_3 = 10.14333127 c_4 = - 0.22475541 c_5 = - 0.00683783 c_6 = - 0.05481717 c_7 = 0.00122874 c_8 = 0.00085282 c_9 = - 0.00000199 return ( ( c_1 + ( c_2 * T ) + ( c_3 * R ) + ( c_4 * T * R ) + ( c_5 * ( T ** 2 ) ) + ( c_6 * ( R ** 2 ) ) + ( c_7 * ( T ** 2 ) * R ) + ( c_8 * T * ( R ** 2 ) ) + ( c_9 * ( T ** 2 ) * ( R ** 2 ) ) ) - 32.0 ) / 1.8