SPC issues Day 1, Day 2, and Day 3 Convective Outlooks that depict non-severe thunderstorm areas and severe thunderstorm threats across the contiguous United States, along with a text narrative. The categorical forecast specifies the level of the overall severe weather threat via numbers (e.g., 5), descriptive labeling (e.g., HIGH), and colors (e.g., magenta). The probabilistic forecast directly expresses the best estimate of a severe weather event occurring within 25 miles of a point. The text narrative begins with a listing of severe thunderstorm risk areas by state and/or geographic region. This is followed by a concise, plain-language summary of the type(s) of threat along with timing that is focused on the highest-risk areas. The rest of the outlook text is written in scientific language for sophisticated users. This technical discussion usually includes a synopsis section to provide a general overview of the weather pattern, emphasizing features that will influence the severe and general thunderstorm threats. Additional sections of the discussion are usually separated by geographic areas. Within these individual geographic areas, the text offers meteorological reasoning and justification for the type of coverage and intensity attendant to the severe weather threat.
SPC also issues a Day 4-8 Severe Weather Outlook that similarly depicts severe thunderstorm threats across the contiguous United States and contains a technical discussion.
Severe Weather Risks
The level of categorical risk in the Day 1-3 Convective Outlooks is derived from probability forecasts of tornadoes, damaging winds, and large hail on Day 1, and a combined severe weather risk on Days 2 and 3.
- TSTM (light green) – General or non-severe thunderstorms – Delineates, to the right of a line, where a 10% or greater probability of thunderstorms is forecast during the valid period.
- 1-MRGL (dark green) – Marginal risk – An area of severe storms of either limited organization and longevity, or very low coverage and marginal intensity.
- 2-SLGT (yellow) – Slight risk – An area of organized severe storms, which is not widespread in coverage with varying levels of intensity.
- 3-ENH (orange) – Enhanced risk – An area of greater (relative to Slight risk) severe storm coverage with varying levels of intensity.
- 4-MDT (red) – Moderate risk – An area where widespread severe weather with several tornadoes and/or numerous severe thunderstorms is likely, some of which should be intense. This risk is usually reserved for days with several supercells producing intense tornadoes and/or very large hail, or an intense squall line with widespread damaging winds.
- 5-HIGH (magenta) – High risk – An area where a severe weather outbreak is expected from either numerous intense and long-tracked tornadoes or a long-lived derecho-producing thunderstorm complex that produces hurricane-force wind gusts and widespread damage. This risk is reserved for when high confidence exists in widespread coverage of severe weather with embedded instances of extreme severe (i.e., violent tornadoes or very damaging convective wind events).
Day 1 Outlook
Day 2 Outlook
Day 3 Outlook