Finding short waves on maps & models

[Patrick Martin]

Does anyone have examples or reccomendations of how to locate a short wave trough on a map or model? I'm not a meteorologist, and for some time now, have been struggling in this area. Among some of the resources, I've used Tim's Weather Forecast book as a reference, but am having trouble applying it in real world scenarios. My understanding is it can be identified by either subtle temp changes and/or wind shifts (please correct me if I'm wrong) and when I'm reviewing 700mb or 500mb charts, have historically had a tough time identifying them. Thank you in advance for any assistance.

 

[Jason Boggs]

Good question Patrick! This website link does a lot better job than myself explaining what a shortwave trough is. I hope it helps you out.

SHORTWAVE EXAMPLE

 

[Patrick Martin]

Thanks Jason, it helps!

 

[Bill Schintler]

RE: Short wave identification

In addition to the aforementioned 700mb and 500mb charts, the water vapor loop is also useful for identifing short waves. The wavelength used by the water vapor imagery is most efficient at showing moisture in the middle- and upper-levels of the atmosphere (10,000 ft and higher). Mesoscale areas of upward vertical motion can often be inferred by examining the water vapor loop, many of which are too small to clearly see on the standard upper-air charts. These typically show up as lighter regions in the image. Often, areas of cyclonic motion - centers of vorticity - can also be identified. Careful identification of lift mechanisms is important for determining the location and timing of convective initiation. In a capped situation, storm development may not occur until until a compact wave provides sufficient lift.

As a specific example, consider the 00Z analysis for tonight, (00Z, 01/06/08):

http://www.spc.noaa.gov/obswx/maps/500_080106_00.gif
http://www.spc.noaa.gov/obswx/maps/700_080106_00.gif

Both the 700mb and 500mb charts show a long-wave trough in the western US, with several short waves embedded within the larger trough. A lead shortwave is translating through the Dakotas, while a second wave is noted over western WY, and a third piece of energy is arriving on the central CA coast.

Compare the upper-air charts to the WV loop:
http://www.ghcc.msfc.nasa.gov/GOES/goeseastconuswv.html

Select "Animation", "30 image loop", and "Animate image above" to get the big picture. It often helps to speed the animation speed up from the default. It is easy to see lift associated with shortwaves as well as other sources of upward motion such as front range of the Rockies.

- bill

 

[Bobby Prentice]

The Storm Prediction Center (SPC) Hourly Mesoscale Analysis page provides an excellent graphic to track short waves.

The 700-400 mb Differential Vorticity Advection graphic (loop) provides the latest analysis of 500 mb height (black contours), 500 mb vorticity (color fill), and 700-400 mb differential vorticity advection (blue contours). Blue contoured areas highlight regions of positive vorticity advection (PVA) which correspond to upward vertical motion within this layer of the atmosphere. The higher the number, the greater the rates of upward vertical motion.

[FONT=Verdana, Arial, Helvetica, sans-serif]The fields shown are calculated using a combination "real-time OA" and "model forecast" method. The SPC runs a 2-pass Barnes surface objective analysis around :05 after each hour, using the latest RUC forecast as a first guess. Next, the surface data is merged with the latest [/FONT][FONT=Verdana, Arial, Helvetica, sans-serif]RUC[/FONT][FONT=Verdana, Arial, Helvetica, sans-serif] forecast upper-air data to represent the best 3-dimensional atmospheric analysis available. Finally, each gridpoint is inputed into a sounding analysis rountine called "NSHARP" to calculate about 100 new fields.[/FONT]

I highly recommend the SPC Hourly Mesoanalysis Page because it provides the best available objective analysis of the current state of the atmosphere over the U.S. Plus, it's a great learning tool for new meteorologists.