Inferenced value starting at 0 for parameter with mean 285, std at .285

I am working on an inverse problem where parameters are being estimated using pyro mcmc. The parameter is normally distributed as below:
k_av_rb = pyro.sample("k_av_rb", dist.Normal(k_av_rb_real, .001*k_av_rb_real))
k_av_lb = pyro.sample("k_av_lb", dist.Normal(k_av_lb_real, .001*k_av_lb_real))
mean is the actual value and standard deviation is .001xmean. The actual value of both parameters is 285.The model is a set of differential equations, solved using scipy.

The results I am getting ( num-samples = 500) is as follows:

I am curious as why the value is starting at 0 when the stdev is just .001x285=.285.