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Create perturbed initial conditions (RESOLVED)

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I would like to create an ensemble with perturbed initial conditions. In particular, I would like to perturb the initial temperature randomly for any grid cell with a number in [-1, 1] Kelvin. Can you please instruct me how to do that? I know that I can use the "ncap2" command to perturb all grid cells with the SAME number, e.g.

ncap2 -s 'where(TT>0.) TT=TT+0.1;' -O

However, I want to perturb each grid cell with a different random number in [-1,1]. I checked the WRF user guide, but I could only find stochastic parametrization schemes, which are not what I am looking for.

Any help would be greatly appreciated. Thanks!
If you're wanting to perturb the initial conditions, you may be able to use NCL to do so. Take a look at this presentation, and specifically starting with slide 40. If you have any NCL-specific questions, there is a separate NCL section of this forum and we have a specialist who answers those questions.