- Will Chicago, IL face tornado risk on August 21?2¢
- Will Houston, TX face tornado risk on August 21?31¢
- Will San Antonio, TX face tornado risk on August 21?<1¢
- Will Dallas, TX face tornado risk on August 21?49¢
- Will Austin, TX face tornado risk on August 21?<1¢
- Will Columbus, OH face tornado risk on August 21?<1¢
- Will Charlotte, NC face tornado risk on August 21?<1¢
- Will Denver, CO face tornado risk on August 21?<1¢
- Will Nashville, TN face tornado risk on August 21?<1¢
- Will Oklahoma City, OK face tornado risk on August 21?<1¢
- Will Memphis, TN face tornado risk on August 21?<1¢
- Will Louisville, KY face tornado risk on August 21?<1¢
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 August 21, 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. 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.
National Weather Service Storm Prediction Center outlooks for August 21 highlighted a 2% tornado probability across parts of northern Illinois and southern Wisconsin, including the Chicago suburbs of Aurora, Naperville, and Rockford plus Milwaukee, driven by modest deep-layer shear of 20-30 knots and sufficient low-level veering to support brief tornadoes amid multicell and marginal supercell storms. Moderate instability and a weak frontal boundary favored this localized threat, while broader severe wind and hail risks extended into the central Plains and Carolinas. Actual reports focused more on damaging winds and prior-day tornadoes in the Northeast, with no widespread Midwest confirmations by late August 21. Updated SPC guidance and National Weather Service local office surveys represent key near-term data that could refine city-specific resolution.