About Soundings:
Here is a good
introduction to reading "skew-T log-p" charts, also known as
soundings. These graphs are generated from data gathered from weather balloons
that are released twice daily at stations all around the globe. Attached to the
balloons are small weather stations that record pressure, altitude, temperature,
relative humidity, wind speed and wind direction, and send the data back to the
station from which it was released. (More info
here on radiosondes.)
How to read the graph:
The red line represents Air Temperature (also known as Environmental Air Temperature
or Ambient Air Temperature).
The green line represents Dewpoint Temperature, or the temperature at which water
in the air condenses and becomes liquid (clouds).
The yellow dashed line represents parcel temperature.
Here is an
explanation of parcel theory. When the parcel temperature is greater than the
air temperature, the atmosphere is unstable and has positive CAPE (discussed below).
In this scenario, the parcel will buoyantly rise until the parcel temperature again
falls below the environmental temperature.
Here is information on
reading hodographs. Hodographs are generated from the wind data provided in the
sounding and show both wind speed and direction. Different hodograph shapes can
indicate the possibility for different kinds of weather (for example, curly hodographs
can indicate the potential for supercells and tornadoes).
Convective Available Potential Energy (CAPE) and Convective Inhibition (CIN)
represent positive and negative potential energy, or buoyancy, in the atmosphere,
respectively. Large CAPE values (>1000 J/kg) indicate an atmosphere conducive to
thunderstorm production. However, a parcel of air must be lifted past a layer of
CIN to become buoyant in a layer of CAPE.
Here is more
info on CAPE and CIN.
Please note that this website initially used Python, including the modules Flask,
Siphon, and Metpy which allowed the user to select any station on any date.
However, I am running my site using Hostgator.com which doesn't allow me to
install these modules on the site...something I wish I found out before I paid
for their service. If you know how to use Flask and would like the code, please
email me at
paul.l.tisch@gmail.com.