Storm Prediction Center Outlooks
Day 1 Convective Outlook
Day 2 Convective Outlook
Day 3 Convective Outlook
Day 4 Convective Outlook
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Day 6 Convective Outlook
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Day 1/2 Operational Conversion (CIG Levels)
| Probability | CIG Level | Tornado | Wind | Hail |
|---|---|---|---|---|
| 2% | None | Marginal | N/A | N/A |
| CIG 1 | Marginal | N/A | N/A | |
| CIG 2 | Slight | N/A | N/A | |
| 5% | None | Slight | Marginal | Marginal |
| CIG 1 | Slight | Marginal | Marginal | |
| CIG 2 | Enhanced | Slight | Slight | |
| 10% | None | Slight | N/A | N/A |
| CIG 1 | Enhanced | N/A | N/A | |
| CIG 2 | Enhanced | N/A | N/A | |
| 15% | None | Enhanced | Slight | Slight |
| CIG 1 | Enhanced | Slight | Enhanced | |
| CIG 2 | Moderate | Enhanced | Enhanced | |
| CIG 3 | Moderate | N/A | N/A | |
| 30% | None | Enhanced | Slight | Slight |
| CIG 1 | Moderate | Enhanced | Enhanced | |
| CIG 2 | High | Enhanced | Enhanced | |
| CIG 3 | High | N/A | N/A | |
| 45% | CIG 1 | Moderate | Enhanced | Enhanced |
| CIG 2 | High | Moderate | Moderate | |
| CIG 3 | High | High | N/A | |
| 60% | CIG 1 | High | Moderate | Moderate |
| CIG 2 | High | High | Moderate | |
| CIG 3 | High | High | N/A | |
| 75%/90% | CIG 1 | N/A | Moderate | N/A |
| CIG 2 | N/A | High | N/A | |
| CIG 3 | N/A | High | N/A |
Day 3 Operational Conversion (Probabilistic)
| Probability | CIG Level | Categorical Risk |
|---|---|---|
| 5% | None | Marginal |
| CIG 1 | Marginal | |
| CIG 2 | Slight | |
| 15% | None | Slight |
| CIG 1 | Slight | |
| CIG 2 | Enhanced | |
| 30% | None | Enhanced |
| CIG 1 | Enhanced | |
| CIG 2 | Moderate | |
| 45%/60% | CIG 1 | Moderate |
| CIG 2 | Moderate |
History of SPC Outlooks
The Storm Prediction Center (SPC) has evolved significantly over the past five decades, adapting its outlook systems to better serve forecasters and the public. Below is a timeline of major developments in SPC convective outlooks.
1974 - First SPC Outlooks
The first SPC Outlooks were established with three categorical levels: Slight, Moderate, and High. These initial outlooks covered only the next 12-24 hours.
1986 - Day 2 Outlooks Implemented
Day 2 outlooks were introduced, extending the forecast period to include predictions for days beyond the initial 24 hours.
May 3, 1999 - Historic F5 Tornado
An F5 tornado passed by SPC headquarters, highlighting the critical importance of accurate severe weather prediction and the work done by forecasters at the center.
2000 - Day 3 Outlooks Added
Day 3 outlooks were introduced, extending the forecast period to the third day, providing extended-range severe weather guidance.
January 24, 2003 - Web Accessibility & Probabilities
A major milestone: SPC Outlooks became viewable on the web for the first time. That same year, the SPC also introduced detailed Tornado, Hail, and Wind Risk probabilities, enabling more precise risk assessment.
2005 - Extended Range Outlooks
Day 4-8 Outlooks were introduced, providing extended-range convective outlooks for the 4th through 8th days of the forecast period.
2010 - EF4 Tornado at SPC
An EF4 tornado passed by SPC headquarters. Debris from this tornado fell on the building, serving as a stark reminder of the destructive power of severe weather.
October 2014 - Risk Category Expansion
The SPC expanded the outlook system to include Marginal Risk and Enhanced Risk categories. This five-category system (Marginal, Slight, Enhanced, Moderate, High) remains in use today as of March 2026.
March 3, 2026 - CIG Scale Implementation
The SPC expanded Tornado, Hail, and Wind risk outlooks to use the new CIG (Conditional Intensity Groups) Scale, moving away from the legacy SIG (Significant) format. This change also included updated graphics on the SPC website.
Academic References
Ernst, S., Ripberger, J., Krocak, M. J., Jenkins-Smith, H.,
& Silva, C. (2021).
Colorful Language: Investigating Public Interpretation of
the Storm Prediction Center Convective Outlook.
Weather and Forecasting.
https://doi.org/10.1175/waf-d-21-0001.1
Cited by: 13
Herman, G. R., Nielsen, E. R., & Schumacher, R. S.
(2018).
Probabilistic Verification of Storm Prediction Center
Convective Outlooks.
Weather and Forecasting, 33(1), 161–184.
https://doi.org/10.1175/waf-d-17-0104.1
Cited by: 41
Krocak, M. J., Ripberger, J. T., Ernst, S., Silva, C. L., &
Jenkins-Smith, H. C. (2022).
Exploring the Differences in SPC Convective Outlook
Interpretation Using Categorical and Numeric
Information.
Weather and Forecasting, 37(2), 303–311.
https://doi.org/10.1175/waf-d-21-0123.1
Cited by: 9
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