def get_precip_data(cell):
    """
    Parse a precip data cell.

    """
    tc = [s.strip() for s in cell.itertext()]
    for i, t in enumerate(tc):
        if t in {'---', ''}:
            tc[i] = float('nan')
        elif t.endswith('%'):
            tc[i] = float(t[:-1])
        else:
            tc[i] = float(t)
    return tc