Seeing = steadiness
Atmospheric turbulence smears fine detail. This tool rates the potential for sharp Moon and planetary views.
Astro Lab
Upper-air stability & planetary detail
Planetary Seeing Forecast
A clear sky can still produce a boiling, blurry planetary image. Compare jet-stream winds, atmospheric shear and near-ground thermal stability over the next three South African nights.
Observing location
Choose a South African location, use your current position, or enter your observing-site coordinates.
m
Transparency = clarity
Cloud, haze and moisture affect how transparent the sky is. Cloud is shown separately and does not inflate the seeing score.
Loading upper-air forecast…
Checking jet-stream winds and atmospheric stability from the surface to 200 hPa.
Seeing forecast unavailable
The upper-air forecast could not be loaded.
Tonight
Cape Town seeing potential
Calculating the steadiest planetary window…
--/100
Loading
Seeing Potential Index
Three-night planetary outlook
Choose a night to compare the best high-power observing windows.
Hourly seeing potential
18:00 through 05:00 for the selected night.
Excellent
Good
Average
Poor
Select an hour to inspect the atmosphere from the ground to the jet-stream level.
Selected hour
Atmospheric profile
Wind and thermal structure for the selected forecast hour.
--
How the Seeing Potential Index works
It is a model-based observing aid, not a direct measurement of seeing in arcseconds.
Jet-stream wind
200 and 300 hPa winds get the largest weighting. Fast upper-air flow often accompanies poorer high-resolution seeing.
Vertical shear
Wind changes between pressure layers are combined with thermal stability. Strong shear in weakly stable layers is penalised.
Ground thermal stability
A large difference between the modelled surface temperature and 2 m air temperature, or rapid cooling, can indicate a restless boundary layer.
Surface wind
Local wind receives a smaller penalty because it can shake the telescope and contribute to low-level turbulence.
Upper-air weather data: NOAA GFS delivered through Open-Meteo under CC BY 4.0. The GFS atmosphere is a numerical weather model with a grid much larger than a telescope site, so local terrain, roofs, concrete, sea breezes and inversions can still dominate the view. Use this index as guidance, then confirm conditions at the eyepiece.