SPC convective outlook risk categories: how to read probability and Conditional Intensity

Categorical outlook · Overall severe risk

Marginal through High summarize coverage and intensity

SPC's familiar five-category scale summarizes the overall risk of organized severe thunderstorms during the outlook's valid period. It is a forecast for an area, not the chance that your address will be hit.

1 · Marginal

Isolated severe thunderstorms are possible, generally with limited organization, longevity, coverage, or intensity.

2 · Slight

Scattered or short-lived severe thunderstorms are possible. “Slight” is a category name, not a promise of slight impacts.

3 · Enhanced

Numerous or persistent severe thunderstorms are possible, with greater coverage than a Slight risk.

4 · Moderate

Widespread, long-lived, and intense severe thunderstorms are likely.

5 · High

Widespread, long-lived, and particularly intense severe thunderstorms are expected.

A separate general-thunderstorm area means thunderstorms are forecast but organized severe storms are not the primary expectation. It is not an all-clear: lightning, heavy rain, localized strong wind, and flooding can still be dangerous outside a shaded severe-risk area.

Probability layers · Tornado, wind, and hail

The hazard maps explain what drives the color

The categorical map compresses several hazards into one view. The tornado, damaging-wind, and severe-hail layers show SPC's best estimate of a qualifying event occurring within 25 miles of a point during the valid period.

Read the percentage as an area-based forecast, not as the odds that one storm will strike one building. A 10% tornado area, for example, does not mean 10% of the shaded land will have a tornado, and it does not mean every storm in the area has a 10% chance of producing one. It means the forecast probability is 10% within 25 miles of any point in that contour.

The category can be driven by one hazard more than another. Two places with the same categorical color may have different main threats, timing, and uncertainty. That is why the individual hazard maps and the written outlook discussion matter.

New in 2026 · Conditional Intensity

Intensity is not the same as probability

NOAA added Conditional Intensity to the Day 1 Convective Outlook in March 2026. The new layer separates two questions that a single risk color cannot fully answer: how likely is a hazard, and how intense could it reasonably become if it occurs?

Conditional Intensity highlights reasonable maximum intensity based on the storm environment and expected storm mode. Tornado and wind use three intensity levels; hail uses two. A highlighted intensity area does not say that the hazard will occur, that every storm will reach that strength, or that every point will experience the displayed maximum.

• Probability asks “how likely?” Use the tornado, wind, or hail percentage contours.
• Conditional Intensity asks “how strong if it happens?” Use the separate intensity legend for that hazard.
• The categorical risk is unchanged. Marginal, Slight, Enhanced, Moderate, and High still summarize overall severe risk.

A lower-coverage setup can therefore carry a higher conditional-intensity signal, while a broad event with many reports may have a lower intensity signal. Do not infer one from the other. Open the full legend and text instead of relying on a cropped screenshot or color alone.

Valid day · Forecast precision

Day 1 is more detailed than Day 4–8

First confirm which day the outlook covers. A Day 1 map covers the near term and includes the most detailed hazard information. Days 2 and 3 retain categorical and probability guidance, while Day 4–8 highlights areas where predictability supports a meaningful extended severe-weather signal.

Longer-range outlooks are broader because storm timing, placement, ingredients, and mode are less certain. A blank extended map means SPC did not outline an area at the product's threshold; it does not guarantee no thunderstorms or severe weather, and later outlooks can add, remove, or shift areas as confidence changes.

Recheck the newest issuance before travel, school, work, or an outdoor event. Use the local NWS point forecast and Area Forecast Discussion for timing and uncertainty, then use any watch or warning for the protective decision.

Outlook, forecast, discussion, watch, warning

Each product changes a different decision

Outlook

A broad forecast of organized severe-weather potential. Use it to identify the valid period, main hazards, uncertainty, and need to keep checking.

Local forecast

Expected conditions and timing for a point or area. Use it to plan the day, but do not treat it as an urgent alert.

Mesoscale Discussion

SPC forecaster reasoning about a developing or changing area. It can discuss watch potential, but it is not a watch or warning.

Watch

Severe thunderstorms or tornadoes are possible across a larger area. Be prepared, know the shelter, and be ready for warnings.

Warning

Severe weather or a tornado is occurring, imminent, or indicated for the warning area. Follow the protective instruction immediately.

A Marginal or Slight outlook can still lead to a warning at your location, and an Enhanced, Moderate, or High outlook does not mean every point will be struck. Once a warning is issued for your location, the warning—not the earlier outlook color—controls the immediate action.

A practical reading order

Turn the map into a plan without overreading it

1. Confirm the valid day and time. Do not use yesterday's map or a social screenshot without its timestamp.
2. Locate your route and destinations. Check the places you will actually be, not only your home ZIP code.
3. Read the categorical area. Treat it as an overall planning signal, not a local warning.
4. Open tornado, wind, and hail layers. Identify which hazard drives the risk and read the percentages correctly.
5. On Day 1, inspect Conditional Intensity. Keep intensity separate from probability and read the legend for the specific hazard.
6. Read the text and monitor alerts. Use the discussion for timing and uncertainty; act immediately if your location enters a warning.