How this works. Each member's hourly-maximum 2–5 km updraft helicity marks the path of a rotating updraft. A storm object is a connected area of UH ≥ 25 m²/s² with at least one point ≥ 75 (the surrogate-severe threshold SPC uses for convection-allowing ensembles), linked hour to hour when consecutive swaths come within 15 km. The shading is the neighbourhood probability: the share of members with UH ≥ 75 within 40 km (25 mi) during the 12Z–12Z day; each area reaching 15% is listed, with the members whose storms ran through it. Lows are minima of smoothed sea-level pressure at least 2 hPa deep, tracked for 12 h or more; the phase space (Hart 2003) reads each low's thermal structure from the 900–300 hPa heights within 500 km every three hours: B for frontal asymmetry, −VT for warm (positive) or cold (negative) core in the lower and upper troposphere. Model storms, not warnings: for those, weather.gov.