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A systematic method is outlined for constructing workable approximations to the joint probability distribution scrP (ψ, ξ) of amplitude ψ and spatial gradient ξ of an active or passive scalar field that is advected by a prescribed isotropically distributed stochastic velocity field and subjected to molecular diffusion. scrP (ψ, ξ) is sampled along fluid-element paths, and closure is obtained by taking a multivariate-Gaussian reference field ψ 0 (x) and distorting it locally in x space so that it exhibits the current scrP (pxi, ξ).