A Sudden, Localized Downdraft
A microburst is a concentrated column of sinking air that plunges out of a thunderstorm and slams into the ground, then spreads outward in every direction — unlike a tornado's rotating winds, a microburst's damage pattern is a straight-line "starburst" pattern radiating from a central point.
By definition, a microburst affects an area less than 2.5 miles across and lasts under 5 to 15 minutes, but winds inside one can exceed 100 mph — comparable to an EF1 tornado.
Wet vs. Dry Microbursts
Wet Microburst
Comes with heavy rain and is driven by evaporative cooling as rain falls through dry air below the cloud, chilling and accelerating the descending air. Common with ordinary thunderstorms in humid climates.
Dry Microburst
Produces little to no rain at the surface — the precipitation evaporates completely before reaching the ground (a virga cloud). Common in arid climates like the High Plains and Southwest, and especially dangerous because there's little visual warning.
Why Radar Can Miss It
Weather radar scans at an angle above the ground, and that angle increases with distance from the radar site — so a shallow, fast-developing microburst near the surface can form and collapse in the gap between radar sweeps, or below the lowest beam the radar can see at a given range. Meteorologists watch for specific radar signatures — like a rapidly descending reflectivity core or a "divergence signature" in Doppler velocity — but a microburst can still strike with only a minute or two of detectable warning.
Why It's an Aviation Hazard
Microbursts are especially dangerous to aircraft during takeoff and landing. A plane flying into the outflow first experiences a headwind (extra lift), then flies into the descending core and a tailwind on the other side — a rapid loss of lift and altitude that has caused fatal crashes. Modern airports use Doppler radar and wind shear detection systems specifically built to catch this signature in the final seconds before it matters.
A Real Case: Delta 191
Microburst risk to aviation isn't theoretical. In 1985, Delta Air Lines Flight 191 crashed on approach to Dallas/Fort Worth Airport after flying through a microburst, killing 137 people. The crash became a turning point for aviation weather safety — it directly led to the FAA mandating onboard wind shear detection systems and Doppler weather radar installations at major airports across the country, which is why airport-specific wind shear alerts exist today.
Macrobursts and the Wider "Downburst" Family
Microburst is actually a subcategory of a broader phenomenon called a downburst — any strong, localized downdraft that spreads out at the surface. A downburst affecting an area more than 2.5 miles across is instead called a macroburst, and can last up to 30 minutes with damage paths stretching many miles — often mistaken for tornado damage since both leave a trail of downed trees, but a downburst's damage pattern fans outward from a point (straight-line), while a tornado's is convergent and twisted (rotational). Storm damage surveyors, including NWS teams, use this fan-versus-twist pattern in fallen trees and debris as one of their primary tools for telling the two apart after the fact.
Frequently Asked Questions
Is a microburst the same as straight-line wind?
A microburst is one specific cause of straight-line wind damage — a sudden localized downdraft. "Straight-line wind" is the broader term for any non-rotating wind damage, which can also come from a gust front or a squall line without a distinct microburst.
How do you know it was a microburst and not a tornado after the fact?
NWS damage survey teams look at the direction fallen trees and debris are pointing. A microburst's damage fans outward from a central point in a straight, diverging pattern; a tornado's damage shows convergent, twisted, and often chaotic directional patterns consistent with rotation.
Can a microburst happen without a thunderstorm?
It's rare but possible — a "dry microburst" can form from virga (rain evaporating before reaching the ground) even from a weak, high-based cloud with little visible storm structure, which is part of what makes them hard to anticipate.
Are microbursts more common in certain seasons?
Wet microbursts peak with regular thunderstorm season (spring through late summer) in humid climates. Dry microbursts are most common in the arid West during the summer monsoon and pre-monsoon period, when high-based storms with little rain reaching the ground are typical.
What to Do
Microbursts arrive with the same general warning as any severe thunderstorm — there's no separate "microburst warning." Treat any Severe Thunderstorm Warning as capable of producing damaging straight-line wind: secure loose outdoor items, stay away from windows, and don't shelter under large trees.
Get Severe Storm Alerts on Your Phone
StormCast pushes Severe Thunderstorm Warnings the moment they're issued for your location.
More from the Blog
A note on this guide: This is general safety information, not medical or professional emergency advice, and specific criteria can vary by region. In an actual emergency, call 911 and follow instructions from local officials and the National Weather Service.