Storm Lab
An interactive laboratory for severe weather. Set the season and draw fronts on a map, shape a sounding by hand, then watch a cloud model build the storm that environment produces, down to the tornado vortex beneath it.
The four views
- Map
- The United States with the ingredients of a severe weather day: the month and the hour, moisture from the Gulf of Mexico, the elevated mixed layer that caps the Plains, the strength of the jet stream, and lows, highs, cold fronts, warm fronts, drylines, outflow boundaries and jet streaks you place and reshape. Overlays show CAPE, inhibition, shear, helicity, the significant tornado parameter and the expected storm type. Play the day forward and storms form, move and decay where the environment allows, with the radar signature of their type and tornado tracks where they produce them.
- Sounding
- A skew-T log-p diagram and hodograph you can drag, or build from controls for surface temperature and dew point, mixed layer depth, cap strength, lapse rate, humidity, shear, and the turning of the wind with height. Every change is analyzed at once: CAPE and CIN for three parcels, the lifted condensation level, shear, storm-relative helicity, Bunkers storm motion, the supercell composite and significant tornado parameters, and the storm type the environment favors, with the reasons. Includes idealized setups and observed soundings from the days of notable tornadoes.
- Storm
- A three-dimensional cloud model runs the sounding forward on your device: a warm bubble or a line of lift starts the convection, and the storm develops as the equations dictate. Watch it on simulated radar reflectivity and velocity, as updraft, rotation or cold pool fields, in a vertical cross section, or in three dimensions from the ground.
- Tornado
- An axisymmetric vortex model of the tornado itself, started from the simulated storm's low-level rotation or from the sounding. Change the parent rotation, the updraft, turbulent mixing and the cloud base, and watch the vortex move between a narrow one-celled core, vortex breakdown and a wide two-celled tornado, with its wind, EF-scale equivalent, pressure drop and condensation funnel.
How realistic it is
The sounding analysis uses the definitions of the Storm Prediction Center's mesoanalysis, and its values for the observed soundings agree with an independent calculation checked against SPC output.
The storm is a numerical simulation, not an animation. The model is compressible and nonhydrostatic, with fifth-order advection, split-explicit time stepping and Kessler warm-rain microphysics, the same class of model Weisman and Klemp used in 1982 to map storm type against instability and shear. Its 1 km grid resolves updrafts, splitting storms, supercells, mesocyclones, cold pools and squall lines. It does not resolve tornadoes, which need grids finer than 100 m, so a tornado is inferred from strong low-level rotation under the updraft and drawn there, and the Tornado view models the vortex separately. Without ice, rain evaporation is reduced so that outflow stays near observed strength.
The map's environment is built from rules rather than simulated, and the storms on the map are a population model that draws the radar signature of each storm type. Both follow the same analysis as the sounding editor, so a storm appears on the map only where a sounding at that point would support one.
Common questions
Is this a forecast?
No. It simulates environments you choose or build. For real weather, see the forecast and warnings from the National Weather Service.
Why did no storm form?
Usually the cap. A rising parcel must push through a layer of warmer air before it can rise freely, and the diagram shades that inhibition in blue. Add lift, lower the cap, add moisture or heat the surface.
What device does it need?
Any current browser. With WebGPU the cloud model runs on the graphics processor, tens of times faster than real time on a typical laptop. Without it, the model runs on the processor on a coarser grid.
Where do the observed soundings come from?
National Weather Service radiosonde launches, from the University of Wyoming upper-air archive, each nearest in time and place to a tornado profiled on this site.