Actual soundings from balloon ascents are available only after the event, but the upwind data on the day itself is invaluable.
However, it is useful to have an idea of the air mass characteristics to be expected in a few days time - a forecast sounding.  
There is a world digital database of  forecast winds, temperatures (dry and dewpoint) covering the next few days. 
It would seem that only data for certain levels is available on the web, eg 1000, 975, 850, 700 mbs etc

The procedure below explains how to interact remotely with the NOAA computer and produce custom data  NOAA website

The examples do not represent any particular day, but are used to illustrate the methods used.

At the NOAA website  you will interact with a remote computer Select an appropriate Lat/Long (example is Midlands)  Click Continue on the screen (example left)

You now get a screen (part of it shown right) where you can select your sounding dataset. Click Go

Next select the time for which forecast is required and also click the optional "Text Listing" and "Graphic size" Enter the access code.   Click "Submit"