Obtain RUC Sounding for PNS:

  1. Go to the Air Resource Laboratory - http://www.ready.noaa.gov/ready/cmet.html
  2. In the ICAO or WMO ID box - put PNS
  3. Click the "Continue" button
  4. Under the SOUNDINGS drop-down choose the "Rapid Update Cycle (RUC 20 km over US)" option.
  5. Click the "Go" button
  6. Time to Plot - choose the "18 UTC" option - for a mid-day forecast.
  7. Type: choose the "Only to 400 mb" option.
  8. Enter the provided Access Code into the Access Code box and click the "Get Profile" button

Typical Sounding for PNS

Cloud Base Caculator
Required Data Entry
Ambient Air Temperature °C  °F 
Ambient Dew Point °C  °F 
Coastal Airport Altitude Meters  Feet 
Calculated Results
Estimated Cloud Base Altitude Feet
Estimated Cloud Base Altitude Meters


The so-called Skew-T/Log-P (or simply Skew-T for short) is an example of the thermodynamic diagram most commonly used in the United States. The Skew-T part of the name comes from the fact that temperature lines on the chart are slanted, while the Log-P is a reminder that pressure does not decrease linearly in the atmosphere. A temperature and dewpoint sounding presented on a Skew-T shows a record of the current atmospheric stability, moisture content, and winds versus altitude. Given surface forecast temperatures, the potential for thermal soaring, including the likelihood of cumulus and/or overdevelopment can then be forecast. Using Skew-T diagrams to their fullest potential requires practice. [Figure 9-10]


There are five sets of lines on a standard Skew-T. Other types of thermodynamic charts, for instance the Tephigram often used in Great Britain, have the same lines, but with a somewhat different presentation. The colors and actual number of lines vary, but the main diagram components should always be present. The following discussion refers to the Skew-T in Figure 9-10.

Horizontal blue lines indicate pressure levels and are labeled every 100 millibars (mb) along the left side of the diagram. On this diagram, the approximate height (in feet) of each pressure level in the standard atmosphere is shown on the right. The actual height of each pressure level varies from day to day. Slanted (skewed) blue lines indicate temperature and are labeled every 10°C along the right side of the isotherm. Thin red lines slanted at an angle almost perpendicular to the temperature lines indicate dry adiabats. (An air parcel following a dry adiabat is changing temperature with height at the DALR.) Thin green lines curving in the same direction as, but at a different angle to, the dry adiabats represent saturated adiabats. (An air parcel that is saturated follows a saturated adiabat is changing temperature with height at the SALR.) The thin orange lines slanting in the same direction, but at an angle to the temperature lines represent the ratio of water vapor to dry air, called the mixing ratio. Lines of constant mixing ratio are labeled in grams of water vapor per kilogram of dry air, abbreviated g/kg.

Over the continental United States, several dozen sounding balloons are launched twice daily, at 00 and 12 Universal Coordinated Time (UTC). These sounding balloons record temperature, humidity, and winds at several mandatory levels, as well as "significant" levels, where notable changes with height occur. In Figure 9-10, the actual temperature sounding (shown in bold red), the actual dew-point temperature (shown in bold green), and the winds aloft (shown in wind barbs on the right side) for this day are shown.

The basic analysis for forecasting the potential for dry thermals based on a sounding is achieved by answering the question, "At what levels is a parcel of air rising from the surface warmer than the ambient air?" Assume on this day, the surface temperature is forecast to reach 23°C. This point is marked on the Skew-T; the parcel of air at 23°C is warmer than the surrounding air and starts to rise at the DALR. When the parcel has risen along a dry adiabat (parallel to the slanted red line) to 900 mb (3,200 feet), it has cooled to 17.2°C, which is warmer than the surrounding air at 15°C. Continuing upward along the dry adiabat, at about 780 mb (7,100 feet) the air parcel and surrounding air are at the same temperature, and the air no longer rises due to its buoyancy. The Thermal Index (TI) at each level is defined as the temperature of the air parcel having risen at the DALR subtracted from the ambient temperature. Experience has shown that a TI should be -2 for thermals to form and be sufficiently strong for soaring flight. Larger negative numbers favor stronger conditions, while values of 0 to -2 may produce few or no thermals. On this day, with a surface temperature of 23°C, the TI is found to be 15-17.2 or -2.2 at 900 mb, sufficient for at least weak thermals to this level. At 780 mb, the TI is 0, and as mentioned, the expectation is that this would be the approximate top of thermals.

Thermal strength is difficult to quantify based on the TI alone since many factors contribute to thermal strength. For instance, in the above example, the TI at 800 mb (6,400 feet) was -1. The thermal may or may not weaken at this level depending on the thermal size and the amount of vertical wind shear. These factors tend to mix in ambient air and can decrease the thermal strength.

It is important to remember that the TI calculated as above is based on a forecast temperature at the surface. If the forecast temperature is incorrect, the analysis above produces poor results. As a further example, assume that on this day the temperature only reached 20°C. From a point on the surface at 20°C and following a dry adiabat upwards, the TI reaches 0 only 1,000 feet AGL, making the prospects for workable thermals poor. On the other hand, if temperatures reached 25°C on this day, thermals would reach about 730 mb (8,800 feet), be stronger, and have more negative TI values.

Source: FAA Glider Handbook

Handy Knowledge:

Surface pressure is normally around 1000 to 1025 mbs

Pressure to Altitude Conversion

Skew T Tutorial - Click Here

Celsius to Farenheit
Conversion Chart
°C   °F
1   33.8
2   35.6
3   37.4
4   39.2
5   41.0
6   42.8
7   44.6
8   46.4
9   48.2
10   50.0
11   51.8
12   53.6
13   55.4
14   57.2
15   59.0
16   60.8
17   62.6
18   64.4
19   66.2
20   68.0
21   69.8
22   71.6
23   73.4
24   75.2
25   77.0
26   78.8
27   80.6
28   82.4
29   84.2
30   86.0
31   87.8
32   89.6
33   91.4
34   93.2
35   95.0
36   96.8
37   98.6
38   100.4
39   102.2
40   104.0
41   105.8
42   107.6
43   109.4
44   111.2
45   113.0