Storm Spotting And Reporting

Radar is powerful, but it cannot see everything. The beam passes over the lowest part of storms at long distances, and it cannot tell a rotating wall cloud from a harmless ragged cloud. That is why the National Weather Service relies on trained volunteers to report what is really happening on the ground. Their eyes turn radar suspicions into confirmed, life-saving information.

What Is a SKYWARN Storm Spotter?

SKYWARN is the NWS volunteer storm spotter program, with several hundred thousand trained spotters across the country. Spotters include emergency managers, firefighters, police, amateur radio operators and ordinary residents.

Local NWS offices offer free training, often in spring and increasingly online. A basic course covers:

• How thunderstorms form and what makes them severe.
• Identifying key storm features and common look-alikes.
• What to report and how.
• Staying safe while observing.

Spotters observe from home or a safe fixed position. Storm spotting is not the same as storm chasing, and it never requires getting close.

What Should Storm Spotters Report to the NWS?

The NWS wants reports of events that meet or approach warning criteria or cause impacts:

• Tornadoes, funnel clouds and rotating wall clouds, with location and direction of motion.
• Hail of any size, especially 1 inch (quarter size) or larger. Compare to coins or balls, or better, measure with a ruler. Avoid vague terms like "marble size."
• Wind gusts of 58 mph or more, measured or estimated, and wind damage such as trees or power lines down.
• Flooding: water over roads, flooded homes, rapidly rising streams.
• Heavy rain totals and heavy snow amounts.
• Damage of any kind, and any injuries or deaths.

Always include what you saw, where (your location and the direction and distance to the event), and when (the exact time). An accurate time makes a report far more useful.

How Do You Identify a Wall Cloud, Shelf Cloud and Scud?

Rain-Free Base

In a supercell, the updraft area is often a flat, dark cloud base with little or no precipitation falling from it. This Rain-Free Base usually sits on the storm's southern or southwestern flank (for storms moving northeast), next to the heavy precipitation core. It is where a wall cloud, and possibly a tornado, will form.

Inflow

Warm, moist air flowing into the updraft often shows up as inflow bands (low bands of cloud feeding into the storm) or a strong wind blowing toward the storm. A sudden increase in inflow can signal intensification.

Wall Cloud

A Wall Cloud is a localized, persistent lowering of the rain-free base, often a few hundred meters to a few kilometers wide. It forms where the updraft draws in very moist, rain-cooled air that condenses at a lower level.

Signs of a dangerous wall cloud:

• Persistent rotation around a vertical axis.
• Rapid vertical motion, with cloud fragments rising into it.
• Location near the rear of the storm, beside the precipitation core.
• Persistence for 10 to 20 minutes or more.

Many wall clouds never produce tornadoes, but most strong tornadoes come from them.

Scud: The Common Look-Alike

Scud are ragged, low cloud fragments that often form beneath storms or along gust fronts. They can look alarming, even hanging down like a funnel, but they are usually drifting with the wind or rising randomly, not rotating. Most false tornado reports come from scud. Watch for organized, persistent rotation before reporting.

Shelf Cloud

A Shelf Cloud is a low, wedge-shaped cloud attached to the leading edge of a thunderstorm's outflow, the gust front. It forms where cool outflow air lifts warm, moist air ahead of the storm.

Shelf clouds are often striking, with layered, terraced structures. They signal strong outflow winds and possibly damaging gusts, followed by heavy rain. Shelf clouds sit on the leading edge of the storm, ahead of the rain, and are pushed along by outflow, while wall clouds hang beneath the updraft near the rear of the storm. Confusing the two is common.

Mammatus

Mammatus are pouch-like clouds hanging from the underside of a thunderstorm anvil. They form where cold, cloudy air sinks into drier air below.

They can look ominous, but mammatus are harmless in themselves. They often appear after a strong storm has passed or on the edges of the anvil. Their presence can indicate a strong storm nearby, but they do not produce tornadoes.

How Do You Report Severe Weather to the National Weather Service?

• Call your local NWS office using the spotter number provided in training, or report through local emergency management.
• Amateur radio SKYWARN nets relay reports directly to the NWS during severe weather.
• mPING (Meteorological Phenomena Identification Near the Ground) is a free smartphone app from NOAA's National Severe Storms Laboratory. Anyone can report precipitation type, hail size, wind damage and flooding. The reports help researchers and forecasters, especially during winter storms.
• Social media reports tagged with location and time also reach many NWS offices.

Local Storm Reports

The NWS collects verified reports and issues them as a Local Storm Report (LSR). SPC compiles them nationally into daily storm report maps of tornadoes, hail and wind. These reports:

• Confirm warnings and help forecasters decide to extend or upgrade them.
• Verify forecasts and warnings after the event.
• Build the climate record of severe weather.