An example showing the Hillsboro, North Dakota EF3 tornadic supercell on August 27, 2016, in which there were two RFD surges. The first RFD surge did not produce a tornado, while the second did. The first RFD surge pushed southward and did not undercut the low-level mesocyclone. Veered flow at 700 mb and a lack of cell mergers were limiting factors, keeping the first RFD surge to the west of the low-level meso. The second RFD surge pushed eastward, undercutting the low-level meso. The second RFD surge was aided by cell outflow and cell mergers during the 15 minutes preceding the tornado. Veered low to mid-level flow, associated with northwest flow aloft, can contribute to a problem in which a supercell’s RFD surge takes place too far west. When this happens, it can be difficult for the RFD to undercut the low-level mesocyclone. This problem makes tornadogenesis more unlikely in summer.
