Instructions for using the HTML sounding display with interactive parcel trajectories

The sounding consists of a Skew-T plot, a hodograph, and a wind plot. Wind directions are always reported with respect to true north. The following thermodynamic indices are also shown, if available:

A parcel may be specified by clicking with the mouse at any point, or by releasing your finger on a touch screen. The parcel will ascend from that point (using the environmental dewpoint at that pressure), and regions of CAPE and CIn will be indicated. The Lifted Condensation Level (cloud base) for the parcel is indicated by a short horizontal black line on the parcel trajectory. Holding down the shift key while clicking with the mouse will bring up a selection window that will allow you to select the initial parcel dewpoint, temperature, and pressure. Click or press on a sounding's button to remove the parcel trajectory. Thanks to Tom Whittaker of the University of Wisconsin for providing the core of the code that performs this task.

(Against Tom's advice, and to facilitate stability calculations using AMDAR soundings that often lack humidity data, iCAPE and iCIn are calculated using the temperature difference between the parcel and the sounding, rather than the virtual temperture difference. According to Doswell and Rasumssen (1994, Weather and Forecasting, 9, pp 625-629), this may cause errors > 30% for values of CAPE below 500 J/Kg and similar errors in CIn, but smaller error for larger values.)

The hodograph shows wind direction (with respect to true north), speed in kts, and height in km.

The sounding has two default altitude ranges, one extending up to 150 mb and the other to 0.5 mb. Each of these ranges can be zoomed by dragging the mouse diagonally across the portion of the Skew-T plot desired. Unzoom by clicking a 'scale' button. (To drag, hold the mouse button down while moving the mouse. When you release the mouse button, the zoomed region will fill the plot.) (The zoomed region will have the same aspect ratio as the main plot, so the red rectangle that appears may not follow the mouse quite the way you think it should.)

On a touch screen, you may zoom the plot using two fingers in the normal way. However, you may need to wait about a second after using any single-finger touch for the multi-touch zooming (and roaming) functionality to work. See touch help for more details.

Other functions are as follows:

Move the mouse or your finger along the sounding to see the following printed at the level of the mouse point (from left to right):

In addition, the following values are indicated below the cursor (reading counter-clockwise from the cursor).

Click on the Load Sounding(s) button to pop up the choose sounding window. In this window you can

Once a sounding is loaded, you can use its button to (re)display it.

The sounding information shown on each button consists of the site name, and a code:

These instructions are copied verbatim from NOAA's GSD Sounding web site.