Surface Map Help: Theta-e and Streamlines

Surface Streamlines and Theta-e contours

Return to the SURFACE IMAGES

Reference: Graphical Guidance pp. 131-141

With this map, you should be able to find the following:

wind flow
areas of high temperatures and moisture via theta-e values
areas where theta-e will increase or decrease
areas of convergence and divergence

Content

Surface Streamlines

Green (Black and White Backgrounds)

Theta-E values in Kelvin

Dashed yellow for black background maps
Dashed red for white background maps
Values contoured every four degrees

Surface Streamlines are simply a "photograph" of the wind. It represents the wind flow at that precise moment. You can check this with the previous map (pressures and temperatures) to see how non-geostrophic the flow is, or how much does it crosses the isobars toward low pressure. A strong cross-isobaric flow often represents a strong system with strong pressure falls and strong areas of convergence.

Theta-e, or equivalent potential temperature, values are found on a thermodynamic diagrams (stuve or a skewt/log p diagram). The process goes like this...

Lift a parcel to it's LCL by way of the temperature through a dry adiabat and the dewpoint though a mixing ratio line until they both intersect. At the LCL, lift the parcel until all the moisture is tapped out (via a wet adiabat line) and becomes dry adiabatic again. Take it back down a dry adiabat to 1000mb and read the temperature. This is equivalent to reading the value of the wet adiabat at the LCL.

Theta-e values are dependent upon temperature and mixing ratio values (moisture) at the surface. Theta-e ridges are important to find because they often are the area where one will find the birth of snow storms, MCS's, supercells, etc. A fine ridge, bulls-eye, or any noticeable feauture of Theta-e values are very important to note because it often depicts where the focus for activity will be since it is the region of the greatest surface instability.

The streamlines can show where values are increasing and can also show something that is also important. Convergence and Divergence. Areas in which the lines pile up are convergent...couple that with high Theta-E values and precipitation is a strong possiblility.

Here is an example of a surface image showing convergence and a Thata-e ridge.

Sea Level Pressure and Temperature	Theta-e and Streamlines	Moisture Divergence and Wind Gusts
Surface Plots	Weather Symbols and Dewpoints	3 Hour Pressure Falls

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