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COLORADO SEVERE WEATHER NETWORK

SKYWARN® Trained Amateur Radio Support Team
Providing Ground Truth Under The Radar

Severe Weather Storm Fundamentals

What Is a Severe Thunderstorm?

A severe thunderstorm is a thunderstorm that produces at least one of the following hazards: hail one inch in diameter or larger, damaging wind gusts of 58 mph or greater, and/or a tornado. These storms can form rapidly, evolve in complex ways, and impact multiple counties in less than an hour.

All thunderstorms contain lightning and heavy rain, but only a subset meet severe criteria, often due to stronger updrafts, deeper storm organization, and favorable wind profiles aloft. Understanding the ingredients that drive storm intensity helps spotters, emergency managers, and the public anticipate which storms are most likely to become dangerous.

Thunderstorm Life Cycle & Types

Most thunderstorms go through developing, mature, and dissipating stages as updrafts and downdrafts evolve with time. Severe storms often maintain a strong, persistent updraft that keeps regenerating new cells or sustaining a single long‑lived storm.

Common convective storm types include single cells, multicell clusters and lines, squall lines and QLCS segments, and supercells with rotating updrafts. Each type has characteristic structures, hazards, and visual clues that are important for spotter training and safe reporting.

Storm Ingredients: Moisture, Instability, Lift & Wind Shear

Four key ingredients control thunderstorm formation and severity: moisture, instability, lift, and wind shear. When all are present and overlap in space and time, the risk for organized severe storms increases significantly.

  • Moisture – Humid air near the surface, often supplied by oceans or the Gulf of Mexico, provides fuel for clouds, rain, and strong updrafts.
  • Instability – When warm, moist air near the ground lies beneath cooler, drier air aloft, air parcels can rise freely, often quantified by CAPE or lifted index values.
  • Lift – Fronts, drylines, outflow boundaries, terrain, and upper‑level disturbances help force air upward to its level of free convection, initiating storms.
  • Wind shear – Changes in wind speed and direction with height help separate updrafts from downdrafts and organize storms into multicells or supercells capable of larger hail, damaging winds, or tornadoes.

Severe storms typically feature higher instability, stronger deep‑layer shear (0–6 km), and focused lift along boundaries or jet‑stream features compared to ordinary thunderstorms. Recognizing these ingredients on satellite, radar, and model guidance is a core skill for both forecasters and advanced spotters.

Convective Storm Types & Hazards

Different storm structures tend to favor different severe weather threats, from brief downburst winds to long‑track supercells. Spotters who can identify storm type gain important context for what hazards are most likely and how long they may last.

Single Cells & Pulse Storms

Single‑cell or “pulse” storms are usually short‑lived, evolving from towering cumulus into a thunderstorm and then collapsing as downdrafts cut off the updraft. They may briefly produce strong winds or marginal hail, especially in very unstable environments, but typically do not stay severe for long without stronger shear.

Multicells, Clusters & Lines

Multicell storms consist of groups of cells where new updrafts form along outflow or boundaries as older cells weaken, often producing repeated rounds of heavy rain, hail, and wind. When these cells grow into lines or bowing segments, damaging straight‑line winds and embedded circulations become primary hazards.

Squall lines and quasi‑linear convective systems (QLCS) can produce widespread wind damage, embedded mesovortices, and occasional QLCS tornadoes, sometimes with limited visibility due to heavy rain. Spotters should watch for bowing segments, surging gust fronts, and areas of rapid cloud base rotation along the line.

Supercells & Organized Severe Storms

Supercells are thunderstorms with a persistent, deep rotating updraft (mesocyclone) driven by strong vertical wind shear. They are capable of producing large to giant hail, destructive straight‑line winds, and the majority of strong and violent tornadoes.

Supercells often show distinct structure such as a rain‑free base, striated updraft, flanking line, and hook‑like radar reflectivity features near the mesocyclone. Some supercells are “high‑precipitation” with heavy rain wrapping around the circulation, making visual identification of tornadoes more difficult and increasing safety challenges for spotters.

Key Severe Weather Hazards

Severe storms can produce a combination of hazards, including large hail, damaging winds, tornadoes, flash flooding, and dangerous lightning. Understanding how each hazard forms and appears visually helps spotters make clear, useful reports.

Large Hail

Large hail forms when strong updrafts suspend and recycle ice particles through regions of supercooled water, adding layers until the stones become too heavy to remain aloft. Severe hail is defined as one inch in diameter or larger, with the largest stones often associated with intense, highly tilted updrafts in supercells.

  • Use common objects (quarter, ping‑pong ball, golf ball) or direct measurement to estimate hail size when safe.
  • Look for roaring thunder, greenish sky tints, and rapidly rising motion near the updraft as possible hail clues.

Damaging Winds & Downbursts

Damaging thunderstorm winds often come from strong downdrafts that spread out as gust fronts, sometimes focused into downbursts or bow echoes. These winds can rival weak tornadoes in impact, toppling trees, power lines, and poorly anchored structures across a broad area.

  • Watch for shelf clouds, boiling cloud motions along gust fronts, and rapidly increasing surface winds as clues to downbursts.
  • Report measured or estimated wind speeds, along with specific damage such as snapped large branches or downed lines.

Heavy Rain & Flash Flooding

Slow‑moving storms or training cells over the same area can produce intense rainfall rates that overwhelm drainage and lead to flash flooding. Urban areas, steep terrain, and burn scars are particularly vulnerable to rapid water rises and debris flows.

  • Report water covering roads, rapidly rising creeks, and stranded vehicles rather than trying to estimate exact depths.
  • Never enter floodwaters; “Turn Around, Don’t Drown” remains a key safety rule for both the public and spotters.

Lightning

Every thunderstorm produces lightning, which can strike miles away from the rain core and before or after the heaviest precipitation. Lightning is a leading cause of storm‑related injuries and fatalities in the United States each year.

  • Follow the “When thunder roars, go indoors” guidance and avoid open fields, tall isolated trees, and metal objects.
  • Spotters should report lightning‑related fires or structural damage when they can do so safely.

Storm Environment & Forecast Tools

Forecasters examine surface observations, upper‑air soundings, satellite imagery, radar, and numerical models to assess severe weather potential. Charts of temperature, moisture, and wind through the atmosphere help reveal instability, shear, and lifting mechanisms that shape storm evolution.

Jet streaks, shortwave troughs, and low‑level jets can enhance lift and moisture transport, supporting nighttime and large‑scale severe weather episodes. Boundaries such as fronts, drylines, and outflow edges often serve as focus areas where storms first develop or intensify.

Spotter Fundamentals in Severe Storms

SKYWARN® training emphasizes recognizing storm structure, identifying hazardous features, and reporting them clearly while maintaining strict personal safety. Spotter observations provide crucial “ground truth” that complements radar and satellite data, especially for low‑level features and evolving hazards.

What to Look For

  • Storm bases, inflow regions, and any organized rotation or persistent lowering.
  • Gust fronts, shelf clouds, and rapid changes in wind, dust, or precipitation.
  • Hail size, wind damage, reduced visibility, and flooding impacts along roads and streams.

Safe Positioning Around Severe Storms

  • Avoid being directly under shelf clouds or in the core of the heaviest rain and hail where winds may be strongest.
  • Maintain escape routes, avoid low‑water crossings, and never put yourself in the path of a bowing line or embedded circulation.

Additional Learning & Training Resources

Many free resources are available to deepen your understanding of severe storms, storm structure, and spotting techniques. These materials complement local SKYWARN® classes and can be used for self‑study or group training.