def get_closest_level_below(search_coord, lvl_elev_dict):
    """
    retrieves the closest level below a given coordinate
    """
    closest_elev_below = None
    for lvl_elev in sorted(lvl_elev_dict):
        if search_coord.Z > lvl_elev:
            closest_elev_below = lvl_elev
        else:
            break
    return lvl_elev_dict[closest_elev_below]