Skew-T sounding

How to use it

Forecast for a place — choose a city, type coordinates or use your location, and the page fetches the next three days of hourly forecasts on pressure levels (1000 to 50 hPa: temperature, dewpoint, wind and height) from Open-Meteo. Slide through the hours; Now jumps back to the current hour. Forecast model picks a particular model (GFS, ECMWF IFS, ICON, UK Met Office, GEM) instead of Open-Meteo’s best match for the place.
Paste a sounding — real radiosonde ascents: at weather.uwyo.edu pick a station and time, choose the Text: List output and paste the table (or open a saved file). Plain rows of pressure height temperature dewpoint [direction speed] work too. Example loads Norman, Oklahoma at 00 UTC on 4 May 1999, the evening of the 3 May tornado outbreak.
The diagram — pressure falls upward on a logarithmic scale (heights above the ground are marked in km); isotherms lean 45° to the right so the profile fits on the page. Red is the temperature, green the dewpoint, orange-brown solid lines the dry adiabats, green dashed lines the moist (saturated) adiabats and blue dotted lines the mixing ratio in g/kg. The dashed black line is a rising parcel: dry adiabatically up to its lifting condensation level (LCL, cloud base), then moist adiabatically. Where it is warmer than the air around it the area is shaded red — the CAPE, energy for updraughts; where it is colder below its level of free convection (LFC) the area is shaded blue — the CIN, the cap. EL marks the equilibrium level where storm tops spread out. Move over the diagram to read pressure, height, temperature, dewpoint, humidity and θ.
Parcel — Surface lifts the air at the ground; Mixed layer the average of the lowest 100 hPa (the usual choice for afternoon storms); Most unstable the level with the highest θe in the lowest 300 hPa (for storms above a cool surface layer). Virtual-temperature correction includes the buoyancy of water vapour, as SPC and MetPy do.
Indices — CAPE, CIN, LCL, LFC, EL, lifted index, precipitable water, freezing level, 0–1, 0–3 and 0–6 km bulk shear, the Bunkers right-mover storm motion, 0–1 and 0–3 km storm-relative helicity, lapse rates, K index and total totals; hover for what each means.
Hodograph — the wind vector at each height, coloured by layer. A long, curved hodograph means strong shear and veering winds — the setting for supercells.
Levels — the sounding as a text list to copy, download, or edit and re-plot.

For aviation weather reports see METAR and TAF decoder; for flying a model today, Can I fly?.

How it is calculated

The thermodynamics follow Bolton (1980) for saturation vapour pressure, the LCL and θe; moist adiabats are the pseudo-adiabatic lapse rate integrated with fourth-order Runge–Kutta in 2 hPa steps. CAPE and CIN integrate R_d·(T_v,parcel − T_v,env)·d ln p on a 5 hPa grid. The page’s tests compare its numbers with textbook values and with MetPy 1.7: the moist adiabat from 20 °C at 1000 hPa reaches −8.5 °C at 500 hPa (MetPy −8.48 °C); for the Norman sounding surface-based CAPE is 2492 J/kg against MetPy’s 2470, CIN −40 against −41, and the LCL, lifted index, precipitable water, K index and total totals agree to within a few per cent or better. Forecast soundings have only the model’s pressure levels (about 20), so they are smoother than a real balloon ascent, and a model’s boundary layer is often a little off — treat small CAPE and CIN values with care.

The reading is a set of rules of thumb, not a forecast.

Privacy

Forecast for a place sends the place’s latitude and longitude to api.open-meteo.com (CORS, no key; Open-Meteo’s data is CC BY 4.0). Pasted soundings are read on the page and never sent anywhere. The place you choose is kept in this browser and shared with the astronomy tools' place picker.