July 12, 2010: Large Hail And The Three-Body Scatter Spike

For the third consecutive evening, isolated severe weather affected a small portion of south central Nebraska on Monday, July 12, 2010. This time around, the main story was an isolated supercell storm that slowly tracked southeast from near Hazard in Sherman County, to south of Ravenna in Buffalo County. 

Severe Weather:

• A roughly 15-mile long (but narrow) swath of quarter to ping pong ball size hail from near Hazard to southeast of Ravenna.

The radar image below depicts reflectivity from the NWS Hastings WSR-88D radar at 620 PM, just as the supercell storm was passing through the Ravenna area in northern Buffalo County.

In this image we are actually looking into the storm at approximately 13,000 feet above ground level (AGL), with the radar actually located 52 miles southeast of the storm, near Blue Hill, Nebraska (location of the black "dot" in the lower right). The purple and white shading in the core of the storm shows very high levels of reflectivty around 70 decibels (dBZ), with values this high often a good indicator of hail within a storm.

"Hail Spike": More intriguing, however, is the long "spike" of reflectivity extending off to the northwest of the storm into Sherman County. In fact, this "spike" is not a reflection of actual precipitation in the area, but instead is a classic example of a radar artifact known as a "Three-Body Scatter Spike", or TBSS. The presence of a TBSS almost always indicates that a storm contains large hail. In simple terms, a TBSS is caused by the radar beam hitting the hail aloft, scattering to the ground below, then scattering back upward, and finally being scattered once again by the hail aloft. The 3 scatterings illustrate the triple reflection, thus the term "three-body scatter spike".

PRELIMINARY LOCAL STORM REPORT...SUMMARY
NATIONAL WEATHER SERVICE HASTINGS NE
801 PM CDT MON JUL 12 2010

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0438 PM     HAIL                 3 SSE ARCADIA           41.38N 99.10W
07/12/2010  E0.75 INCH       SHERMAN            NE   PUBLIC
            HAIL UP TO PENNY SIZE

0534 PM     HAIL                 3 E HAZARD              41.09N 99.02W
07/12/2010  E1.00 INCH       SHERMAN            NE   PUBLIC
            QUARTER SIZE HAIL

0536 PM     HAIL                 9 ESE LITCHFIELD        41.11N 98.99W
07/12/2010  E1.00 INCH       SHERMAN            NE   LAW ENFORCEMENT
            QUARTER SIZE HAIL

0618 PM     HAIL                 3 SE RAVENNA            41.00N 98.87W
07/12/2010  E1.00 INCH       BUFFALO            NE   STORM CHASER
            QUARTER SIZE HAIL

0618 PM     HAIL                 1 N RAVENNA             41.04N 98.91W
07/12/2010  E0.75 INCH       BUFFALO            NE   TRAINED SPOTTER
            DIME SIZE HAIL

0625 PM     HAIL                 5 SE RAVENNA            40.98N 98.85W
07/12/2010  E1.00 INCH       BUFFALO            NE   PUBLIC
            QUARTER SIZE HAIL

0631 PM     HAIL                 3 S RAVENNA             40.98N 98.91W
07/12/2010  E1.50 INCH       BUFFALO            NE   LAW ENFORCEMENT
            PING PONG SIZE HAIL

0741 PM     HAIL                 4 W LONG ISLAND         39.95N 99.61W
07/12/2010  E0.75 INCH       PHILLIPS           KS   PUBLIC
            DIME SIZE HAIL AND HEAVY RAIN