Sonoma Wings Hang Gliding

Interactive Balloon sounding (Skew-T) plots

Forecast Temperatures:
Current GMT time:
The plot request page:
How to read the plot page:
Tutorial: on lapse rates and using a sounding diagram to track a rising parcel of air.
Tutorial: on SkewT charts. Power Point slides.
Tutorial: on SkewT charts. .PDF document.
Presentation: on forcasting using SkewT & blipmaps .Power Point slides.
Skew-T with help: Try this plot for Medford. There is on-screen help showing how to work the chart, similar to my instructions, below. To change location, click the "load soundings" button.

Lat/Lon for local flying sites

Latitude and Longitude must be entered as shown here (without the quote marks). You can copy/paste from this screen.

Location         Lat.   Long.      t/o Alt.   Temp. to use  Elev.
St Helena       "38.668,-122.628"    4200       Santa Rosa  130
Crazy Crk     	"38.770,-122.570"    1000       Lakeport   1400
Elk           	"39.276,-122.942"    4000       Ukiah       600
Hull-Timberline	"39.511,-122.939"    5900       Ukiah       600
St John	        "39.424,-122.689"    6300       Red Bluff   360
Diablo	        "37.880,-121.919"    3700       Concord      25

Instructions:

Either print out this page, or open the plot page in a separate window so you can have these instructions handy while you interact with the plot
Get the day's max. temperature for the site you want. Jot it, and the reporting location's Elev. (see above), down.
Copy the site coordinates, above, to the clipboard:
- - Windows: highlight the text between quotes (click/drag), then press Ctrl-C.
- - Mac:
In the plot request page:
- Highlight the "den" site identifier, then press Ctrl-V to paste in the coordinates for your site.
- Enter a "5" for the number of hourly plots to create.
- Enter the Zulu time you want this plot to be for. For us, 20 GMT will be 12noon PST / 1PM PDT.
- Click the "Java-based plots" button.

You'll see your plot. At the bottom of the plot is the description (location & time) of the plot you're looking at. Below that are buttons for each hourly plot. Click each button to see how the profile changes over time. If you want to get a different set of plots, you don't have to leave this page. Do this:

In the plot page, click "Load Sounding(s)" button at bottom-left. This will pop up a small window where you can enter parameters:
- - Choose a site: Either an identifier (here's a short list), or lat/lon (see list at top of this page).
- - Start date: in GMT (7 hrs later than PDT, 8 hrs later than PST).
- - Number of hours to load: Each hourly plot will have a button at bottom of plot page.
Enter parameters, then click "Op40" button to create the plots.

Working with a plot

Move your cursor up and down on the plot. You'll see the values for the dew point (blue trace), temperature (red trace), and wind (right edge) change. The cursor position's current altitude and temperature are shown next to the cursor itself. Move the cursor until the value for altitude and temperature match what you jotted down for the day's max temp., then click to get a magenta trace - what a parcel of air lifting off from that point will do. You can redo this magenta trace if you like. Try a guess at what the temp will be at launch altitude for the time you're viewing.

The further the magenta line is to the right of the red line, the stronger the lift will be. Where the two lines cross is where the thermals should top out. You'll also see a short black horizontal line showing the theoretical cloudbase. If the red and magenta lines cross lower than the theoretical cloudbase, it's a blue day (no clouds). If the red and blue (dew point) lines cross, that's a solid cloud layer.

Click buttons (below the plot) for other times to see how the thermal profile will change during the course of the day.

In the top-left of the plot is a "bulls eye". This is another way to view the wind profile. The wind trace gives you a good overview of the wind at all altitudes. As you move your cursor up and down through different altitudes, you'll see a red dot moving on the trace in the "bulls eye" showing the wind reading at that altitude. Bear in mind that this "bulls eye" shows wind as blowing TO, instead of blowing FROM. In other words, a red dot at the right of the "bulls eye" shows a west wind (coming from the left). You get the same information from the wind barbs to the right of the plot. Wind direction is from the flag end of the wind barb, and the number and size of the hash marks tells you the wind strength.

Zooming in on the plot

Since you're only interested in altitudes up to 15,000 ft. or so, you can enlarge the lower portion of the plot.

Move your mouse to the bottom-right corner of the plot.
Hold down the left mouse button and drag the mouse toward the upper-left. You'll see a rectangle being drawn that shows what the zoom-in will be.
When the rectangle goes up as high as you want, release the mouse button and you'll have an exploded view of that rectangle.
To do it over again, click the button at the bottom of the plot labled "150mb scale".

To learn more about reading these "Skew-T" plots, Click Here.