Meteorology For Scientists & Engineers Web Resources

Upper-Air Soundings / Stability [ Resources | Exercises]

Lab Exercises

Goals:

Enhance understanding of thermodynamic diagrams
Gain confidence in interpreting soundings
Learn definitions and application of severe-weather stability indices

Method: Independent work by the students, utilizing computer spreadsheets, web-based tutorials, and other tools.

Examine soundings and severe-weather stability indices presented on the web
Compute selected stability indices

A. Comparison of On-line Soundings

List the Station IDs (3 or 4 letter) and City Names of the 6 rawindsonde sites closest to your university ( UWy ).
Note that ICAO station IDs officially have 4 letters, but often the first letter is omitted if it is obvious.
The first letters most common in N. America are:
- C = Canada
- K = continental USA
- P = Alaska & Hawaii
What are the other rawinsonde stations in your State or Province (skip this question if the answer was already fully listed in question C1)?
Retrieve and print the current sounding for Maniwaki, Quebec (CWMW), in the following 4 thermo diagrams, and discuss how the sounding looks in each diagram:
- Skew-T (UWy - set Type of Plot to "GIF Skew-T")
- Stuve (UWy - set Type of Plot to "GIF Stuve")
- Emagram (NIU - select Emagram for station CWMW)
- Tephigram ( UQAM )
Repeat the previous question, but for the upper air station nearest to you (except don't get the tephigram). Also, at what pressure height is the tropopause, based on the sounding you plotted.

B. Stability Indices

How are the following stability indices defined, and what threshold value for each of them indicate a severe thunderstorm? ( NWS , and see the other links listed in the Resources section above )
1. CAPE
2. K-index
3. Lifted-index
4. Convective Inhibition (CIN)
5. Helicity
Using current stability indices.
1. Use the national radar image to find a band of strong thunderstorms ( NWS , or Intellicast , UCAR/RAP ), especially in the central or SE portion of the USA.
2. Then go back to the rawinsonde station map ( UWy ), select a station just SE of the line of storms, and retrieve and print the Skew-T sounding. This is normally in the unstable air ahead of the storms. (Tip: if there are no thunderstorms, such as often happens in winter, than pick Miami Florida (MFL) or San Juan Puerto Rico (TJSJ) as the rawinsonde station.)
3. For this sounding, what are the values of CAPE, K-index, Lifted-index, Convective Inhibition (CIN), and Helicity? (abbreviations explained). Do these values indicate that thunderstorms are likely? (tables relating stability index to storm intensity: NWS , or see last column of page 2, from weathergraphic )
Plot a couple of the analysis maps of key stability indices ( FSL/WRF or SPC or UNISYS ). Which parts of N. America would most likely favor strong thunderstorms, based on these diagrams?
Compare and discuss your severe weather forecast from D3 with any warning or watch boxes that have been produced by the NWS Storm Prediction Center.

Resources

Thermodynamic Diagrams of Current Soundings

Skew-T Diagrams:
- from OhioState: explanation , soundings & indices for all US & Canadian sites .
- from NCAR: soundings, indices & hodographs for all US & Canadian sites .
- from UNISYS: explanation , soundings, indices & text for US sites .
- from FSU: soundings & indices for N. America .
- from TAMU: soundings for N. America .
- from NIU: soundings & indices for N. America .
- from UWy: soundings & indices for N. America .
- from EC via UNBC: vertical profiles for selected stations in W. Canada
Emagram / Pseudoadiabatic Chart:
- from U.Wash: UIL, OTX, SLE, MFR .
- from NIU: soundings in N. America .
Stuve Diagrams
- from AMS DataStreme Project: blank diagram , soundings for selected US sites .
- from FSU: soundings .
- from NIU: sondings in N. America .
- from UWy: soundings & indices for N. America .
Tephigrams
- selected sites in Canada: Edmonton AB , Alert NWT , Montreal PQ .
ACARS/AMDARS sounding data from commercial aircraft: NOAA FSL , .
Hodographs of wind:
- from FSU .
Plots soundings on the fly (world-wide) :
- UWy: soundings (Skew-T, Stuve, hodograph) by clicking on map.
  - with explanations of indices .
- NIU : soundings (Skew-T, emagram, Stuves, or hodographs) by entering stn ID.
Arctic soundings (U Wisc.-Milwaukee)
Archived sounding data ( FSL )
Station IDs for Rawinsonde sites:
- Map showing Station IDs in any continent ( UWy )
- Map showing Station IDs ( letter & number IDs) N. America ( FSU )
- Map showing NWS sounding sites ( NWS )
- List of Station ID names and numbers in N. America ( FSU )
- Station Look-up from NWS .

Blank Thermo Diagrams (useful for hand plotting)

Blank graphs, useful for hand-plotting of real soundings:
- skew-T gif1 / gif_color / pdf_color (from Riddle, UCSD/Scripps)
- tephigram gif / pdf (from Evans, U. Colorado)
- Stuve gif1 / gif2 / pdf2 (from R. Fovell, UCLA)
- emagram gif1 / pdf1 / gif3 / tiff3 / pdf3(from R. Stull, UBC)
- emagram (zoomed for PBL) gif / tiff / pdf (from R. Stull, UBC)
- theta-Z gif / pdf (from R. Stull, UBC)
- theta-Z (zoomed for PBL) gif / tiff / pdf (from R. Stull, UBC)
Sounding data in ascii text form (for plotting on blank thermo diagrams)
- from: AMS , UIL , UWy , FSU ,

Tutorials and Manuals

Tutorials:
- What is a radiosonde? Brief Intro , historical photos .
- From the UK: Comparison of tephigram, skew-T, Stuve thermo diagrams .
- Tutorial on how to read tephigrams ( UNBC , U.Leeds UK , Project Atmos-Canada.pdf )
- From FSU: How to read Upper Air codes .
USA Handbook #3 on Rawinsonde and Pibal Observations .
NWS Rawinsonde network info .
Software to plot soundings ( from UCAR )

Stability & Severe Weather Indices

Excellent explanation (NWS Louisville)
Stability indices and weather radar (NWS)
Definitions (Sirvatka COD)
Explanations and Definitions (Australian Severe Weather Assoc.)
Definitions and Interpretation (Ohio State U) , and contour plots .
Live excellent contour plot forecasts of many severe storm indices over most of US (Texas A&M U) with definitions and explanations how to interpret.
Live contour plots of stability indices, and definitions - (UNISYS)
Live contour plots of stability indices for Canada (EC)
Forecast contour plots of total-total index and precipitable water (COLA/IGES) .
Live vertical profiles (upper air soundings) with tables of indices & definition - (UNISYS)
Live satellite-derived indices (NWS Western Region) and from CIMSS