Thermal Ridges and troughs

[Tim Johnson]

Also known as Temperature ridges or troughs, I had a question regarding the operational use of this data.

weatherprediction.com lists the following in relation to this.

thermal ridges often are indicators of higher instability regions especially if WAA and moisture advection are associated with the thermal ridge.


Looking at the big picture, when does it become pertinant to analize thermal ridges (and troughs) in the grand scheme of forcasting severe wx? Is it something that should just be glanced at to determine its importance, or something that should be included as a rule?

[Glen Romine]

It can be looked at as a part of identifying the main instability axis when used in concert with other features in a composite map. Here is an example of what a typical composite map might look like for the morning before a severe weather event in the southern plains:

http://www.atmos.uiuc.edu/~romine/img/sp_spring_svr_wx.png

The 850 mb thermal axis is the same thing as the thermal ridge - as in the axis of warmest temperatures. You can see that it is west of the surface moisture axis - and the greatest instability is located between these two axes.

Glen

[Tim Johnson]

Is it better to view this feature on the 850 mb chart or surface (or both)?

[Glen Romine]

Is it better to view this feature on the 850 mb chart or surface (or both)?

Short answer - use 850 mb. Long answer - above is a chart for a morning condition that would be favorable for a severe wx event later in the day. As such, if you looked at the surface at this time - you'd probably find the warmest axis to be to the right or along the moist axis where the air didn't cool as greatly, whereas the dry air to the west of the dryline is likely very cool in the morning, with a shallow radiation inversion, but will rapidly warm by later in the day. In fact, the 850 mb temperatures are generally used by mets to forecast the days high temperatures. So, since we are most interested in what conditions will be like during peak heating - it is more valuable to look at the 850 thermal ridge. I've also overlayed in the image above the 700 mb temerature - the magnitude of the contour varies seasonally - but the countour clearly peaks northward to the east of the 850 mb axis. the closer these two axes are to each other - the more of a problem capping might be over the instability axis.

Glen

[Tim Johnson]

Thanks for the info Glen. The graphic helps quite a bit. The more I lean about weather and forcasting the more it amazes me; all the various components that can change a given scenario. Seems like the more I grasp about wx the more I realize I don't know. I think thats part of what keeps me plugging along though.

Thanks again for taking time to share some insight on this!