What does HIGH risk mean in SPC outlooks?

HIGH is SPC's top level 5 of 5 — a major severe-weather outbreak is expected. Long-track violent (EF3+) tornadoes, derecho-magnitude wind, or 3″+ hail are likely. SPC issues HIGH only ~3-4 times per year on average; it triggers maximum operational posture from NWS, EMAs, and broadcast meteorology.

What historical events were HIGH risks?

Notable HIGH risks include April 27 2011 (Super Outbreak — 360+ tornadoes, EF4/EF5 across Alabama), December 10 2021 (Western Kentucky — long-track EF4), March 24 2023 (Mississippi Delta — Rolling Fork EF4), and several days during the active May 2024 plains pattern. HIGH-risk days are referenced by date in the operational community for years afterward.

What Does HIGH Risk Mean from SPC? — Top of the Convective Outlook Scale

What Does HIGH Risk Mean from SPC? — Top of the Convective Outlook ScaleHIGH is the top of the SPC convective outlook scale (level 5 of 5). A major severe-weather outbreak is expected — long-track violent (EF3+) tornadoes, derecho-magnitude wind, or 3″+ hail. SPC issues HIGH only ~3-4 times per year.HIGH is the top of the Storm Prediction Center's categorical convective outlook (level 5 of 5). A HIGH risk means a major severe-weather outbreak is expected — long-track violent (EF3+) tornadoes, derecho-magnitude wind, or 3″+ hail. SPC issues HIGH only ~3–4 times per year on average; it triggers maximum operational posture from NWS, EMAs, and broadcast meteorology.HIGH severe probabilityThe formal SPC threshold for High Risk is a 30%+ tornado probability with the hatched (SIG = EF2+) overlay, or equivalent extreme wind or hail probability. HIGH is conceptually "we expect a major outbreak today" — not "many strong storms" but "a regional, life-threatening severe-weather event."How rare HIGH isHIGH is issued ~3–4 times per year on average. Not issued at all in some quiet years (2018 had only one); issued multiple times in active spring seasons (2011 had several; 2024 had multiple). HIGH days are remembered by name in the operational severe-weather community.HIGH vs. MDTHIGH is reserved for major outbreaks with strong-to-violent (EF3+) tornado potential or derecho-magnitude wind clusters. MDT (level 4) is widespread severe storms with significant (EF2+) tornadoes likely. The jump from MDT to HIGH represents the difference between "major severe day" and "this could be one of the worst days of the decade."What HIGH risk triggersHIGH is the maximum-posture tier. NWS forecast offices in the area run continuous operations, broadcast meteorologists cut all programming, school districts close early, EMAs run full operations with shelter activation messaging, and the SPC issues frequent Mesoscale Discussions through the event. Public messaging is direct ("this is a life-threatening situation").Notable HIGH risk days

April 27, 2011 — Super Outbreak. 360+ tornadoes, multiple long-track EF4/EF5 across Alabama. The benchmark modern HIGH risk.

April 14, 2012 — Central plains outbreak. Long-track tornadoes Oklahoma to Kansas.

December 10, 2021 — Western Kentucky outbreak. Long-track EF4 tornado from Arkansas through Tennessee into Kentucky.

March 24, 2023 — Mississippi Delta. Rolling Fork EF4 tornado.

Several days during May 2024 — Active plains pattern, multiple HIGH risk days.

HIGH-risk days are referenced by date in the operational community for years afterward.See the full SPC convective outlook guide for the complete scale and the supercell / MCS / QLCS glossary.

Frequently asked questions

What does HIGH risk mean in SPC outlooks?: HIGH is SPC's top level 5 of 5 — a major severe-weather outbreak is expected. Long-track violent (EF3+) tornadoes, derecho-magnitude wind, or 3″+ hail are likely. SPC issues HIGH only ~3-4 times per year on average; it triggers maximum operational posture from NWS, EMAs, and broadcast meteorology.
How rare is a HIGH risk?: Issued ~3-4 times per year on average. Not issued at all in some quiet years (e.g., 2018 had only one); issued multiple times in active spring seasons (2011 had several; 2024 had multiple as well). HIGH days are remembered by name in the operational severe-weather community.
What is the difference between HIGH and MDT?: HIGH (level 5) is reserved for major outbreaks with strong-to-violent (EF3+) tornado potential or derecho-magnitude wind clusters. MDT (level 4) is widespread severe storms with significant (EF2+) tornadoes likely. The jump from MDT to HIGH represents the difference between "major severe day" and "this could be one of the worst days of the decade."
What operational posture does HIGH risk trigger?: HIGH is the maximum-posture tier. NWS forecast offices in the area run continuous operations, broadcast meteorologists cut all programming, school districts close early, EMAs run full operations with shelter activation messaging, and SPC issues frequent Mesoscale Discussions through the event. Public messaging is direct: "this is a life-threatening situation."
What historical events were HIGH risks?: Notable HIGH risks include April 27 2011 (Super Outbreak — 360+ tornadoes, EF4/EF5 across Alabama), December 10 2021 (Western Kentucky — long-track EF4), March 24 2023 (Mississippi Delta — Rolling Fork EF4), and several days during the active May 2024 plains pattern. HIGH-risk days are referenced by date in the operational community for years afterward.

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