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Understanding National Weather Service “Severe Weather Outlook”

Example NWS SPC Severe Weather Convective Outlook
Example SPC Day 1 Convective Outlook
Severe weather outlooks, also commonly referred to as convective outlooks, are issued daily by the National Weather Service (NWS) Storm Prediction Center (SPC) in both text and graphic form.

Severe Weather Outlook Periods

Convective outlooks are divided into four periods:
Day 1 The risk of severe weather today through early morning of the following day. Day 1 forecasts are issued five times daily: 06z (around midnight), 13z (around sunrise), 1630z (mid-morning), 20z (mid-afternoon), and 01z (early evening).
Day 2 Day 2 continues from the end of Day 1 (tomorrow morning) for the next 24 hours. Issued twice daily: 07z (around midnight) and 1730z (around noon).
Day 3 The forecast for the subsequent 24 hours. Day 3 forecasts are issued daily by 0830z on standard time and 0730z on daylight time (after midnight).
Days 4–8 A severe weather area depicted in the Day 4–8 period (issued at 10z, early morning) indicates a 30% or higher probability of severe thunderstorms (a 30% chance that a severe thunderstorm will occur within 25 miles of any point).

Severe Weather Outlook Risk Categories

The severe weather outlook graphics display up to six color categories reflecting an increasing likelihood and/or severity of severe weather.

General Thunderstorms

The light green shading depicts a 10% or higher probability of non-severe or near-severe thunderstorms during the valid period.

Severe Category 1 – Marginal (MRGL)

The dark green shading indicates a marginal risk of severe thunderstorms during the forecast period. This means a:
  • 2% or greater tornado probability, or
  • 5% probability of severe hail (≥1″) or severe wind (≥58 mph / 93 km/h)

Severe Category 2 – Slight (SLGT)

The yellow shaded area indicates a slight risk of severe thunderstorms during the forecast period. This means a:
  • 5% or greater tornado probability, or
  • 15% probability of severe hail or severe wind, with or without a 10% or greater probability of hail 2″ or larger or wind gusts 75 mph or greater (120 km/h or greater)

Severe Category 3 – Enhanced (ENH)

The orange shaded area indicates an enhanced risk of severe thunderstorms during the forecast period. This means a:
  • 10% probability of any tornado, with or without a 10% or greater probability of an EF2+ tornado, or
  • 15% probability of any tornado, or
  • 30% severe hail or severe wind probability, with or without a 10% or greater probability of hail 2″ or larger or wind gusts 75 mph or greater, or
  • 45% probability of severe hail or wind

Severe Category 4 – Moderate (MDT)

The red shaded area indicates a moderate risk of severe thunderstorms. This means a:
  • 15% tornado probability and a 10% or greater probability of an EF2+ tornado, or
  • 30% probability of any tornado, or
  • 45% severe wind probability and a 10% or greater probability of wind gusts 75 mph or greater, or
  • 45% severe hail probability and a 10% or greater probability of hail 2 inches or larger, or
  • 60% severe wind probability, or
  • 60% severe hail probability, with or without a 10% or greater probability of hail 2 inches or larger

Severe Category 5 – High (HIGH)

The fuchsia shaded area indicates a high risk of severe thunderstorms. This means a:
  • 30% tornado probability and a 10% or greater probability of an EF2+ tornado, or
  • 45% or greater probability of any tornado, with or without a 10% or greater probability of an EF2+ tornado, or
  • 60% severe wind probability and a 10% or greater probability of wind gusts 75 mph or greater
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The latest severe weather outlooks are published on the Storm Prediction Center’s official outlook page.

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