How this simulator works
Meteorologists don't just look at "will it storm today" — they look at a small set of atmospheric parameters that decide whether storms will fire, whether they'll organize into supercells, and whether those supercells will produce tornadoes. This tool exposes six of the most important ingredients as sliders so you can see how each one shifts the outcome.
The metrics you're computing are the same ones on the SPC mesoanalysis and the post-event write-ups of historic outbreaks. When STP climbs above 3, meteorologists start using words like "particularly dangerous situation." When it approaches 8, they're describing 1999 Bridge Creek or April 27, 2011.
Formulas used. STP (fixed-layer) = (SBCAPE/1500) × ((2000-LCL)/1000) × (SRH01/150) × (BulkShear06/20) × ((-CIN-50)/-50). EHI = SBCAPE × SRH01 / 160,000. Storm mode is a coarse decision tree on deep-layer shear plus CAPE. These are simplified relationships from Thompson et al. (2003, 2007) and Craven & Brooks (2004); they capture the shape of tornado potential well but they don't replace a real forecast.
The six ingredients
Instability CAPE
Convective Available Potential Energy — the "fuel" that lets air parcels accelerate upward. Higher CAPE means taller and stronger updrafts. Values above ~2500 J/kg support severe storms.
The cap CIN
Convective inhibition — a stable layer aloft that acts like a lid. A small cap concentrates energy so storms explode late in the day; too much cap and nothing forms at all.
Deep-layer shear 0–6 km
The change in wind speed and direction from the surface to about 6 km. Strong deep-layer shear tilts the updraft away from the rain, letting a supercell survive for hours instead of dying in its own rain-cooled outflow.
Storm-relative helicity SRH
A measure of low-level rotation available to the storm. When SRH is high — think 300+ m²/s² — the mesocyclone can stretch a low-level vortex into a tornado.
LCL height cloud base
The altitude where rising air becomes saturated (cloud base). Low LCLs mean the cool downdraft doesn't cut off the low-level circulation — a classic ingredient of Dixie Alley tornado outbreaks.
Surface moisture Td
Dewpoint. It sets both CAPE and LCL indirectly — a 70°F dewpoint over the Plains is a red flag; a 40°F dewpoint means the air is too dry to fuel much of anything.
Try these real-atmosphere presets
Click any preset above the sliders to load real-world parameter sets — the ingredients that produced classic Plains outbreaks, Dixie Alley HP monsters, high-based landspout days and cap busts. Then move a slider and watch the STP change.
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