High-Risk Severe Weather Outlooks and Types of Thunderstorms in the U.S.

Severe weather is an ever-present danger in the United States, and accurate forecasting is crucial to save lives and property. The National Oceanic and Atmospheric Administration’s (NOAA) Storm Prediction Center (SPC) provides severe weather outlooks and high-risk forecasts. By analyzing atmospheric data and weather models, the SPC tries to anticipate extreme weather conditions that can cause significant damage.

Severe Weather Outlooks and High-Risk Forecasts Issued by SPC

The SPC issues daily severe weather outlooks to inform people about thunderstorm threats for the following day. The outlooks are divided into four categories: general, marginal, slight, and enhanced risks. A general risk means that thunderstorms are possible but not severe, while an enhanced risk means that numerous severe thunderstorms are likely.

A “high-risk” severe weather outlook is one of the most urgent messages issued by the SPC. A high risk is the highest level of severity on a scale from 1 to 5 in daily severe weather outlooks issued by the SPC. When a high risk is issued, it is due to concerns about a tornado outbreak with numerous intense and long-tracked tornadoes or a long-lived derecho-producing thunderstorm complex that produces hurricane-force wind gusts and widespread damage.

From 2000 through 2021, the SPC issued a Level 5 high-risk forecast average of two to three days each year. April and May combined accounted for nearly two-thirds of all high-risk days from 2000 through 2021. Almost three-quarters of the high-risk forecasts were accurate, while only seven were considered “busts.” On high-risk days, people should take unprecedented action to protect themselves and have a dependable way of getting severe weather watches and warnings.

Types of Thunderstorms in the U.S.

With the arrival of warmer weather in the U.S., people can expect to see more thunderstorms. Thunderstorms have similar life cycles but can vary in size and impact. There are four types of thunderstorms: single-cell thunderstorms, multi-cell thunderstorms, squall line thunderstorms, and supercell thunderstorms.

Single-cell thunderstorms are short-lived and produce brief heavy rain, lightning, and thunder. Multi-cell thunderstorms consist of a group of individual storms that work together, are more intense, and can last for several hours. Squall line thunderstorms form a long line of storms along a cold front, are known for strong, damaging winds, hail, and heavy rainfall, and can produce tornadoes.

Supercell thunderstorms are the most severe and dangerous type; characterized by a rotating updraft known as a mesocyclone. The least common but most powerful type of storm can produce very large hail, damaging winds, and tornadoes.

Severe Weather Forecasting in the United States

The battle between warm and cold air masses during spring leads to severe weather across the United States. The National Weather Service has a department called the Storm Prediction Center (SPC) responsible for issuing severe thunderstorm and tornado watches and convective outlooks.

The SPC issues Day 1, Day 2, and Day 3 Convective Outlooks that show non-severe and severe thunderstorm threats across the United States. The SPC uses colors and numbers to specify the level of severe weather threat and also provides a text narrative of risk areas by state or region.

There are six categories of severe weather risks issued by the SPC: general risk, slight risk, marginal risk, enhanced risk, moderate risk, to high risk. They are shaded on a map of the United States. The SPC also uses a “Hatched Area” to indicate a risk of significant severe weather for tornadoes, wind, or hail.

The abc27 weather team uses SPC’s outlooks to inform their audience of severe weather risks. With accurate forecasting and timely warnings, people can prepare themselves and protect themselves from severe weather conditions that are becoming more frequent and intense due to climate change.

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