Easter 2011 Severe Weather Outbreak

April 24, 2011

Many residents of the Big Country will remember the Easter of 2011 for a long time.  Just ask those in Abilene and Baird.  The day began innocent enough as low clouds persisted through much of the morning hours.  Eventually the broke through the cloud cover, setting the stage for a severe weather outbreak.  By the end of the day, much of Abilene had been pounded by extremely large hail up to the size of softballs and several picturesque tornadoes had affected areas from Potosi, to Baird, to Moran.

The Setup

Image 1.  Surface features (3 PM CDT) that played a role in the development of severe weather across the Big Country on Easter Sunday, April 24, 2011.

A stationary front was draped across the Big Country from near Wichita Falls, to Abilene, to Big Spring.  Cooler air and north winds on to the north of the front provided a nice contrast to the very warm and humid conditions to the south.  A dryline extended south from this front near Sweetwater, to Sterling City, to Iraan, separating the very dry West Texas air from the rich Gulf moisture in the warm sector (Image 1).

A stationary front was draped across the Big Country from near Wichita Falls, to Abilene, to Big Spring.  Cooler air and north winds on to the north of the front provided a nice contrast to the very warm and humid conditions to the south.  A dryline extended south from this front near Sweetwater, to Sterling City, to Iraan, separating the very dry West Texas air from the rich Gulf moisture in the warm sector. 

Aloft, an upper level storm system was moving across the southern Rockies into the Plains.  This feature helped to precondition the atmosphere by cooling temperatures aloft and increasing instability (essentially the energy needed for thunderstorm development).  This upper level system also provided strong winds in the mid levels of the atmosphere, increasing deep layer wind shear.  The cooling temperatures aloft juxtaposed with the warm, humid air at the surface resulted in Convective Available Potential Energy (CAPE) values exceeding 3500 J/kg.  Effective shear values generally ranged from 40 to 50 kts across the region as well.  The combination of these factors proved to more than adquate to support organized severe convection for much of the afternoon and evening hours (FWD 00Z Sounding April 25).  These factors prompted the issuance of a Severe Thunderstorm Watch for much of the central and northeast counties of the forecast area.  This watch was upgraded to a Tornado Watch a few hours later.

The Event:

By mid-afternoon storms quickly developed over the Big Country and quickly became supercellular.  Storms developed from just south of Sweetwater, across the Abilene area and toward Albany and began moving northeast.  The first tornado touched down at approximately 3:30 PM CDT north of Baird.  Luckily, the damage from this tornado was confined to tree limbs.  This  tornado lift but the same storm later produced a brief touchdown roughly 5 miles north of Moran in southeast Shackelford County. 

Image 2. Cross section of Abilene Hail Storm at 4:39 PM CDT.  Notice the very high reflectivities at and above 30,000 ft.

Another supercell became tornadic as it moved south of Abilene.  This storm produced two brief tornado touchdowns near Potosi but no damage was reported.  The most damaging storm of the night followed to the northwest of the Potosi storm (Image 2).  This cell developed south of Sweetwater and moved along Interstate 20 crossing Abilene just after 4:30 PM CDT, dropping very large hail across much of the southern half of the the city (see radar loop).  Hail up to the size of softballs was reported in southern Abilene from near the mall to the airport.  This hail shattered countless windows and produced dings and dents in numerous vehicles and roofs. At the Mall of Abilene, there were reports of 60 to 80 vehicles with shattered windows throughout the parking lot.  This was likely the scene in many areas.  In addition to the hail and tornadoes, very heavy rainfall was observed due to these storms training along the stationary frontal boundary producing wave after wave of heavy rain.  Abilene Regional Airport recorded 2.42 inches of rain in around 2 hours time.  This resulted in widespread urban flooding across Abilene with the most significant impacts found in low lying intersections and underpasses.

The Potosi and Abilene cells continued to move to the east-northeast with the latter eventuallly overtaking the former in northern Callahan County.  Shortly after this cell merger the rotation within the storm increased significantly with another tornado forming north of Baird.  This multi vortex tornado was captured on videoby several storm chasers and looked impressive on film but luckily, like the other tornadoes, was over open country with no observed damage.

Another very impressive supercell developed in the southern Big Country just after 6 PM CDT near the Taylor-Runnels County line.  This cell tracked in an easterly direction dropping a swath of very large hail from Wingate in northern Runnels County to Novice in northwest Coleman County.  Rotation began to increase on this storm as it moved into the northern Heartland where it eventually produced a brief tornado 2 miles southwest of Silver Valley in Coleman County.

As this wave of thunderstorms moved out of the Big Country and Heartland, a second batch of thunderstorms began to develop along the dryline which remained to the west of an Ozona to Sterling City line.  These cells intensified very rapidly and quickly became severe tracking across the many of the areas that saw thunderstorms earlier in the afternoon and evening.  A Severe Thunderstorm Watch was reissued around midnight for areas along and north of the Colorado River.  These storms continued to exhibit rotation but their impacts were confined to large hail.  These storms finally moved out of the forecast area around 2 AM CDT, bringing to an end a very wild Easter Sunday.

The Aftermath:

When all was said and done, the National Weather Service in San Angelo determined that 6 tornadoes touched down within the WFO San Angelo domain.  Despite the impressive structure of a few of these tornadoes, no damage was observed so they will go down in the record books with ratings of EF-0 on theEnhanced Fujita Scale.  The most significant impact during this entire event was the large hail in Abilene where widespread vehicle and roof damage occurred.  No injuries were reported with this weather event but it will definitely go down as an Easter to remember for many Big Country residents!

All said, there were 7 weak tornadoes in the San Angelo County Warning area during this event.  Only minor tree damage was surveyed and all have been rated as EF-0.

They are as follows:

3:28-3:32 PM CDT - 6 N Baird in north central Callahan County (EF-0)
3:55-3:58 PM CDT - Ibex (5 N Moran) in southeast Shackelford County (EF-0)
4:22-4:27 PM CDT - 3 ENE Potosi in eastern Taylor County (EF-0)
5:04-5:07 PM CDT - 3 Miles NNW Baird in norh central Callahan County (EF-0)
5:15-5:18 PM CDT - 7 N Baird in north central Callahan County (EF-0)
5:24-5:35 PM CDT - 6 N Baird in north central Callahan County (E-F0, multi-vortex)
8:27-8:32 PM CDT - 15 S Oplin (2 SW Silver Valley) in northern Coleman County (EF-0)

The remaining storm reports from this event can be found in the Summary LSR.

 Photo Gallery: 

Tornado near Potosi.  Photo by: Shelby Tucker	Funnel cloud; location unknown.  Photo by:  Chase Calhoun	Wall cloud over Lytle South.  Photo by:  Bonnie Hall	S Abilene on Industrial Road.  Photo by:  Merry S.	Indian Run Apartments.  Photo by:  Eric Peoples
Baseball size hail.  Photo by: Wayne McCormick	Hollis Dr and S 27th.  Photo by: Jenise Shepard	Large hail on Plover Lane.  Photo by:  Brice West	Quail Hollow Apartments.  Photo by: Terri Collum	South Abilene Baseball size hail. Photo by: Jason Hummel
Pheasant Drive.  Photo by:  Ken Weinkauf	Robertson and Chimney Rock.  Photo by: Matt and Robin Swarz	Lone Star Drive.  Photo by:  Paul Gottfried	Chimney Rock Road.  Photo by: Tim Tracy	San Miguel Drive.  Photo by: Denise Caudle
Pheasant Drive.  Photo by:  Ken Weinkauf	Robertson and Chimney Rock.  Photo by: Matt and Robin Swarz	South Abilene Baseball size hail. Photo by: Jason Hummel	Dyess Air Force Base.  Photo by: Beth Maddox	Darrell Dr near Warwick Apts.  Photo by:  Cody Bullock