Michael,

First, welcome to soaring. All of us were beginners once, and it's
great that you are asking questions. The things that come to mind with
rain:

Is there a possibility of lightning? If so, stay clear. Composite
ships are especially prone to lightning damage and I seem to remember
hearing of damage to the metal control linkages in one glider.

High performance gliders will suffer more loss of L/D in rain due to
their laminar flow airfoils -- which rain makes non-laminar flow, with
higher drag.

Will visibility stay VFR? Aside from seeing other traffic, is there
any danger of loss of spatial orientation?

A good general rule: If it feels dangerous, it probably is. At a
minimum, err on the side of believing that until you confirm
otherwise.

Martin