Synoptic/mesoscale conditions before and during the events

Often, these precipitation "bombs" in the Eta occur under synoptic conditions favorable for heavy rain and MCS development. Sometimes heavy rain does occur somewhere, as it did both nights the model forecast an event in the case shown here from the 12 UTC 26 July model run. This poses a considerable forecast challenge.

To get a feel for what is going on in the model in these precipitation events, click the Display Graphic buttons below to view four-panel displays of forecast heights, winds, and temperatures at 500, 700, 850, and 925 hPa. The images are very large. You can maximize the pop-up windows and, depending on your screen size, scroll around the window to see each panel. All four panels contain 3-hour precipitation contours, which may be used as reference locations to help in seeing the juxtaposition of features at different levels.

You may want to step through the loops, stopping to examine what's going on at each time in the loop. After seeing the first two times in each loop, stop and think about where you would forecast the heaviest rains over the next 12 hours if you believed these fields, realizing of course that in reality you would also be looking at a wide range of observed data as well as other model products such as soundings, cross sections, and larger-scale and upper-tropospheric conditions, all not shown here. After going through all the frames, play the loop quickly to view the evolution.

Click the Display Graphic button to the left to display the SD loop in a separate window

Click the Display Graphic button to the left to display the KS loop in a separate window

Some particularly interesting features:

• Both events are preceded by strong low-level warm fronts, a broad region of low-level convergence, veering wind profiles, and the Kansas event has a notable 700 hPa hot prod advecting across behind a light rain area.
  
• The low-level winds quickly back as afternoon height falls occur over the high plains, reducing the warm advection (winds more parallel to isotherms) but increasing regional-scale convergence.
  
• A low forms at all levels, most pronounced at 700 hPa, with the flow accelerating and backing, increasing convergence.
  
• The low straddles the warm front and wraps up on the warm front, drawing cooler air around the back side.
  
• Late in the life cycle, cooling occurs around the entire system at 850 hPa, washing out the front. This is more pronounced in the SD case. The KS case has the 850 hPa cooling more in the center of the system, occluding it rather than washing out the gradient.
  
• The KS case develops a pronounced 925 hPa mesohigh under the heavy rain area and a leading 850 hPa mesolow.
  
• Both cases develop a warm core at 500 hPa in the region of heaviest precipitation.