Instructions for using the html sounding display with interactive
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.
- These values are taken directly from model output, if
- CAPE (Convective Available Potential Energy) in J/Kg
- CIn (Convective inhibition) in J/Kg
- PW (Precipitable water) in Kg/m^2
- Helic (storm-relative helicity) in m^2/s^2 (not currently available)
- These values are calculated directly from the sounding data by the
- TT (Total Totals index)
- KI (K index)
- SI (Showalter index)
- LI (Lifted index) of the mixed layer (assumed to be the lowest
100 mb of the sounding)
- LCL (Lifted Condensation Level) of the mixed layer (assumed to be the lowest
100 mb of the sounding)
- These values are calculated when the user specifies a parcel (see
- iCAPE (interactive CAPE) - approximate
CAPE of the parcel
- iCIn (interactive CIn) - approximate CIn
of the parcel
- iLCL (interactive Lifted Condensation Level) of the parcel
(Against Tom's advice, and to facilitate
stability calculations using AMDAR soundings that often lack humidity
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
In addition, the following values are indicated below the cursor
(reading counter-clockwise from the cursor).
- The pressure in mb, and the pressure altitude (the altitude in a
standard atmospherethat corresponds to this pressure, in
km and feet. (For AMDAR data, the time, bearing and range from
the airport are also shown.)
- The dewpoint in Celsius (and also Farenheit below 750 mb).
- The temperature in Celsius (and also Farenheit below 750 mb).
- The wind direction (with respect to true north)
and speed in knots.
- A highlighted wind barb.
- A highlighted portion of the wind speed curve.
- A highlighted portion of the hodograph
- T: the temperature in Celsius (and Farenheit).
- Theta: the potential temperature.
- The pressure altitude (the altitude in a standard
atmospherethat corresponds to this pressure, in ft.)
- The pressure in millibars.
Click on the Load Sounding(s) button to pop up the
choose sounding window. In this window you
Once a sounding is loaded, you can use its button to (re)display
- Click on or touch a button to clear the display, and
display one sounding.
It generally takes less than a second for an already-loaded
sounding to reappear.
- Shift-click one or more buttons to
add additional soundings
to the plot. (Shift-click means hold down the shift key while
clicking the mouse button.)
- Control-click a sounding's button to remove
the sounding and its button.
The sounding information shown on each button consists of the site
name, and a code:
R indicates a RAOB sounding
P indicates a Profiler sounding
A indicates a sounding from a model analysis
Fn indicates a sounding from a model n-hour
- For instance "DEN(F9)" indicates that the
sounding data are from a model forecast based on an analysis from 9 hours
before the indicated valid time.
Dn indicate AMDAR ascent or
descent soundings, respectively.
Please send questions about this page to one or more of the following people.
- webmaster-amb.gsd for
technical questions about the display (such as a blank screen)
- Brian Jamison
for questions about soundings and the SkewT display in
general, and about RAOB soundings
- John Brown for
questions about model soundings (types of models, available
forecasts, latency, etc.)
Last modified: Wed Feb 24 22:24:50 GMT 2016