reading charts

[timeless]

lm by no means knowledgeable on the subject but lve acquired an interest in trying to predict weather types that cause thunderstorms/lightning.

 

about all l know so far is a little about reading lifted index and l have been using the following site:

 

http://www.weatheronline.co.uk/cgi-bin/expertcharts?LANG=en&MENU=0000000000&CONT=euro&MODELL=gfs&MODELLTYP=1&BASE=-&VAR=lftx&HH=6&ARCHIV=0&ZOOM=0&PERIOD=&WMO=

 

however going by what l see on weatheronline it doesnt seem to match what netweathers "will it thunder" charts show. lm currently situated in the west midlands, and from what lm seeing netweather predicts reasonable potential matching today at the second on monday where as weather online doesnt give the same readings, in fact its showing more potential on tuesday and wednesday yet the lifted index charts on weatheronline are currently showing none over land at this moment.

 

suffice to say ld like a little information on reading other types of charts that are used to predict potential for electrical storms, any information and help would be greatly appreciated.

[Vorticity0123]

Hi Timeless,

 

A good question it is. There are many ways to assess chances on severe thunderstorms, each with their own advantages and disadvantages. The Lifted Index is indeed a good way to assess whether severe weather development is possible or not. In short, this index tells something about the amount of instability in the atmosphere. I will not go into more detail on this variable in this post.

 

CAPE

 

Another widely used and good indicator for severe weather prediction is CAPE (Convective Available Potential Energy). The CAPE, as the name says, indicates the amount of 'energy' an air parcel would contain if would be lifted vertically in the atmosphere. Generally, CAPE values above 1500 J/kg indicate thunderstorms are possible. The higher the CAPE, the higher the chance that thunderstorms will develop.

 

Of a side note, the explanation given above is far too simple to fully understand the variable. If you would like to gain more information about this phenomenon, check the severe guide given below:

 

http://www.estofex.org/guide/

 

On Wetterzentrale, there are also forecasts of CAPE and Lifted Index (LI) available from the GFS. Below is an example of such a chart for next Wednesday:

 

GFS CAPE + LI (valid: Wednesday, 2 April, 18Z). The values for CAPE are indicated by the colour shadings (in this case mostly blue/green), and the LI-index values are given by the grey/white contours.

 

The link to these charts can be found below:

 

http://www.wetterzentrale.de/topkarten/fsavneur.html

 

On the map above, an area of high CAPE-values along with negative LI-values can be seen extending from the south of Paris to Liverpool. This does not necessarily indicate that thunderstorms are likely in that area, but elevated chances do exist.

 

"Modelweather"

 

Another useful tool for thunderstorm predictability is the so-called "modelweather" (or Modellwetter in German). The forecasted weather by a model for every grid cell of a model is calculated and indicated by a symbol. For example, below is the GFS-modelweather analysis for Wednesday 18Z:

 

GFS "Modellwetter" (valid: Wednesday 2 April, 18Z). The different symbols indicate the weather the model "expects" at every grid cell.

 

What can be seen is that the GFS-model does show some risk on thunderstorm development on the 2nd of April near Liverpool. Moreover, showers are also possible in central Wales. Note that those charts should only be used as an indication of the expected weather, and not as a real forecast.

 

The link to the charts is given below:

 

http://www.wetter3.de/animation.html (select Modellwetter ZE in the dropdown menu).

 

Wind shear

 

A more easily understandable variable physical-wise is wind shear. Wind shear is the difference in wind speed and direction between two height levels in the atmosphere. As a rule, wind speed increases with height. The change in wind direction with height is more variable, though. 

 

Generally speaking, high levels of wind shear (thus a high difference in wind speed/direction with height) are favourable for thunderstorm development. Hence, it is an important parameter for thunderstorm development.

 

Below is an example of such a wind shear map:

 

Wind shear analysis from CIMSS. The arrows indicate the direction of the shear, while the yellow contours indicate the values of wind shear between two predefined levels.

 

Because I don't know of any wind shear forecast maps of Europe alone, the only map I can present is the actual shear map given above. Sorry for the inconvenience.

 

When you want a forecast for wind shear over a given day, it is also possible to compare wind maps of two different heights in the atmosphere and simply look at the difference in wind direction and strength. However, deciding which heights to take is a tricky one, as different height choices can result in different shear values.

 

The link to the shear maps is given below:

 

http://tropic.ssec.wisc.edu/real-time/europe/winds/

OR:

 

http://tropic.ssec.wisc.edu/

 

ESTOFEX

 

ESTOFEX is a very useful site/organization for assessing risks on thunderstorm development. ESTOFEX provides a map of risks on severe weather (including thunderstorms) of Europe, which is updated frequently. ESTOFEX works with a classification system, where category 1 indicates a slight risk on severe weather, category 2 indicates a high risk on severe weather. Finally, category 3 indicates there is also a risk on "extremely severe weather". The link to the site, as well as a more thorough description of the different warning levels can be found in the link below:

 

http://www.estofex.org/

 

Furthermore, the website contains in-depth technical discussion about the areas highlighted as "danger zones". The discussion deals with the synoptic analysis (the analysis of the weather pattern present in terms of high/low pressure) and various severe weather parameters (including CAPE, LI and many more).

c

Finally, the website contains an elaborate guide (though possibly difficult to understand for ones with little background in meteorology) on the different severe weather indices, ingredients needed for thunderstorm development and a lot of other subjects related to severe weather. The link to the guide can be found below:

 

http://www.estofex.org/guide/

 

I hope this post helps you a little in order to be able to understand and predict severe weather events. There are many different indices regarding severe weather development which can be explored as well. Quite often those indices are related to each other in some way, but the links are usually rather complex. If you have any questions or remarks left, feel free to ask/tell.

 

EDIT: Added wind shear analysis for a more complete overview of severe weather parameters.

 

Sources:

http://en.wikipedia.org/wiki/Convective_available_potential_energy

http://www.weatheronline.co.uk/reports/wxfacts/Thunderstorm-Probability.htm

http://www.spc.noaa.gov/sfctest/help/sfcoa.html

http://www.weatheronline.co.uk/reports/wxfacts/CAPE---Convective-Available-Potential-Energy.htm

http://www.wetter3.de/animation.html

http://www.wetterzentrale.de/topkarten/fsavneur.html

http://www.estofex.org/

http://en.wikipedia.org/wiki/Wind_shear

http://tropic.ssec.wisc.edu/

Edited March 30, 2014 by Vorticity0123

[timeless]

thankyou for the very informative post, just what l was looking for.