A dry microburst is a small, intense downburst that reaches the surface with little or no rain, typically from a high-based storm whose precipitation evaporates in a deep, dry subcloud layer.
How it forms
The setup is a deep, well-mixed boundary layer beneath a shallow layer of midlevel moisture, the pattern seen on a Skew-T as the inverted-V sounding. Rain or graupel falls out of the elevated moist layer and drops into very dry air below. Evaporation and melting chill the parcel rapidly, and negative buoyancy accelerates the now-colder air toward the surface.
In the study by Evenson and Mecikalski, environments favorable for dry microbursts typically feature midlevel relative humidity above about 50 percent between 500 and 400 mb, a temperature drop of 30 degrees Celsius or more between 850 and 500 mb, and surface humidity below about 40 percent. That is a shorthand for saying: enough moisture aloft to make precipitation, and enough dry air below to evaporate almost all of it before it can reach the ground.
How to recognize one
Visually, the storm often looks unimpressive. High cloud bases, virga hanging from the base like a translucent curtain, and no obvious rain reaching the surface are typical. The first sign at the ground is often a rapidly expanding dust ring or a plume of debris kicked up by the outflow. Spotters call this the dust foot, the dry counterpart to the wet event's rain foot.
On radar, dry microbursts can be nearly invisible in reflectivity, but Doppler velocity often reveals descending convergence aloft and strong divergence at the surface. GOES-based nowcasting products developed at NOAA use environmental proxies like the boundary layer lapse rate and midlevel moisture to flag areas where dry microbursts are plausible.
How forecasters use the concept
Forecasters watch for inverted-V soundings, elevated mixed layers extending well above the surface, and afternoon heating over the intermountain West or High Plains. DCAPE, a measure of how much negative buoyancy a downdraft parcel can accumulate, is one of the more useful ingredients-based indicators. Values in the range of a thousand to fifteen hundred joules per kilogram, paired with a dry subcloud layer, favor strong dry outbursts.
For aviation, dry microbursts are particularly hazardous around Denver, Salt Lake City, Albuquerque, and similar western terminals. Terminal Doppler radars and low-level wind shear alert systems in these places were installed largely in response to dry microburst events.
What the setup does not guarantee
Not every inverted-V sounding produces a damaging dry microburst. Many storms in these environments simply drop virga and dissipate, or the outflow stays weak because the precipitation shaft never becomes strong enough. Ingredient-based diagnostics tell you the environment is capable, not that a strong burst is certain.
It is also worth remembering that dry microbursts do not exclude tornadoes or hail from the same day. In parts of the High Plains, a hybrid environment can allow supercells with hail cores in one part of the region and pure dry microburst outflow in another. Reading each storm's individual radar and visual signature matters more than pattern-matching to the regional climatology.