1. An Investigation of the 26 July 2006 Downburst near Spearville, Kansas
Jennifer Ritterling
National Weather Service
Dodge City, KS

2. Wind Damage 26 July 2006 Photo by Jeff Hutton
On the evening of July 26, a severe downburst damaged a home 2 miles north of Spearville. Owner of the home received some minor injuries as a door blew off its hinges inside, striking him in the leg.
Photo by Jeff Hutton

3. Wind Damage 26 July 2006 Photo by Jeff Hutton
SVR warning was out for the county, but nothing more than 70 mph winds mentioned.
Photo by Jeff Hutton

4. Wind Damage 26 July 2006 Photo by Jeff Hutton
Other storms that evening were severe, with mph gusts, but only one produced the property damage that this one did.
Photo by Jeff Hutton

5. 250 mb Analysis from 12Z
Jet was well north of western KS. Flow over the southwestern CONUS was light under ridging. Profilers at Granada and McCook showed that winds at this level stayed around kts up through the time of initiation.

6. 500 mb Analysis from 12Z
Light flow also evident at mid levels. A shortwave trough was evident at 12Z in the OR/ID area. By the time of the storms around 23Z, water vapor loop has the shortwave still out in Colorado.

7. 12Z Sounding
Quite a lot of mid-level moisture, but considerably drier at lower levels.

8. Contaminated 00Z sounding
was launched
while
convection was
ongoing.
Sounding was launched as the convection was ongoing. Sonde got sucked up into the storms and convectively contaminated.

9. 12Z sounding modified for 22Z surface conditions
12Z sounding was modified for surface conditions at DDC at 22Z, as convection was starting.

10. Potential Downburst Type?
Intermediate/”Hybrid”
Large Positive Area
Elevated Dry Layer
Some points about this sounding: There is a decent positive area. Little or no cap left. There is a dry adiabatic layer that is at least 1500 m below LCL. There is also a moist layer in the mid troposphere. And a elevated dry layer above 4600 m. From Microbursts: A Handbook for Visual Identification by Caracena, Holle, and Doswell, this fits criteria for intermediate or hybrid microburst soundings. In fact, doing a back of the envelope cacluation of Pyor’s Hybrid Microburst Index, this sounding comes up with a value of over 16, indicating Downbursts likely.
Moist Layer
Little Capping Inversion
Dry Adiabatic Layer

11. Thanks to Jon Finch for assistance with analysis
Surface Analysis at 21Z
At the sfc at 21Z, there was a weak trough of low pressure extending southwest to northeastward across KS. There was a boundary evident across the southeastern portion of DDC’s CWA. Could be a trough axis, but there does appear to be a weak temperature gradient between P28 and DDC and GCK.
Thanks to Jon Finch for assistance with analysis

12. Storm initiation
Boundary was evident on radar just before storms initiated.

13. Storm Initiation
Storms got started just before 2130Z down in Meade/Clark counties.

14. Thanks to Jeff Hutton for looping help
Radar Loop
Storms came up through the DDC area, producing moderately severe winds (tree branches down in town). DDC ASOS reported a 47 kt max. Storm that would eventually produce the damaging downdraft passed just east of the airport and continued northeastward.
Thanks to Jeff Hutton for looping help

15. 0.5 Velocity at 2352Z
Good low level divergence couplet around the time of the damage. Some smaller pixels may be a smaller scale feature, or just traffic on the highway.

16. Conclusions Forcing mechanisms for this event are somewhat unclear
Sounding showed good potential for intermediate/hybrid type of downbursts
Was this particular event predictable?
Why did this particular storm produce such damage while others were minimally severe???
In this case it seemed that the thermodynamic profile was more of a factor than shear or winds, with the sounding showing good indicators for hybrid microburst potential. As for why this storm and not the others, it seems that we don’t really have enough data at the meso or even storm scales to make that kind of determination.