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This market will resolve to "Yes" for each listed city that falls within a tornado probability area rated ≥2% in the NOAA Storm Prediction Center Day 1 Convective Outlook on September 4, 2026. Otherwise, this market will resolve to "No". The SPC Day 1 Convective Outlook assigns tornado probability percentages (2%, 5%, 10%, etc.) to geographic areas across the US. If a city's coordinates fall inside any area rated 2% or higher, that city resolves "Yes". If a city is outside all tornado probability areas, or only within areas rated below 2%, that city resolves "No". The SPC outlook is published as machine-readable geographic data (GeoJSON) at spc.noaa.gov. Each city's coordinates and the polygon boundaries are publicly verifiable. Borderline cases can be independently confirmed using the polygon data (excluding the hatched SIGN overlay, which is not a probability rating) and the city's listed coordinates. The point-in-polygon test is performed on unprojected WGS84 (EPSG:4326) coordinates, which is the native coordinate system of the SPC GeoJSON data. Resolution is based on the scheduled 01:00 UTC Day 1 Convective Outlook update issued on the following UTC calendar day. The SPC Day 1 outlook covers a 24-hour period from 12:00 UTC to 12:00 UTC the following day. Subsequent revisions published after that scheduled update will not be considered. If the SPC outlook is not published or is unavailable, the market remains open until data is available. The resolution source for this market is the NOAA Storm Prediction Center at spc.noaa.gov.
The Storm Prediction Center's September 4 Day 1 outlook established a slight severe risk across the southern Great Lakes and mid/upper Ohio Valley into the Mid-Atlantic, driven by a frontal boundary, moderate instability, and northwesterly flow aloft. A 2% tornado probability contour covered parts of central Ohio and adjacent Indiana, with Columbus, Fort Wayne, and Dayton among the larger centers highlighted, while broader marginal areas extended to Detroit, Chicago, and the Carolinas. Damaging winds dominated the threat profile per probabilistic graphics, consistent with observed severe thunderstorm warnings that day. Low tornado odds reflected limited shear and discrete storm modes rather than supercell-favorable setups. Resolution hinges on official SPC or NWS verification of tornado watches, warnings, or confirmed events within the 24-hour period.