def get_url(center, valid, product):
    """Return the URL given the provided options."""
    fn = "%s_00.00_%s00.grib2.gz" % (product, valid.strftime("%Y%m%d-%H%M"))
    if center == "mtarchive":
        uri = ("https://mtarchive.geol.iastate.edu/%s/mrms/ncep/%s/%s") % (
            valid.strftime("%Y/%m/%d"),
            product,
            fn,
        )
    else:
        uri = ("https://mrms%s.ncep.noaa.gov/data/2D/%s/MRMS_%s") % (
            center,
            product,
            fn,
        )
    return uri