Rare Wake Low Event Produces Severe Wind Gusts,
Damage in Amarillo on June 28

If you live in Amarillo, you may have been awoken by the sound of howling winds and possibly security alarms early Tuesday morning. During the late evening of Monday, June 27 and the early morning of Tuesday, June 28, a convective complex moved across the southern Texas Panhandle, providing badly needed rains to many locations.  In fact, it was the first measureable rain at Rick Husband International Airport in Amarillo since May 11 -- over 47 consecutive days!  The storms also produced a severe wind gust to 58 mph in Deaf Smith County late on the evening of June 27.  As the strongest convection moved east of Amarillo, stratiform rain (i.e. light to occasionally moderate rain) continued behind the strongest storms.  It was in this area of stratiform rain that a sustained period of very strong winds developed between about 2:30 a.m. and 4:00 a.m. and impacted Potter and Randall Counties, including Amarillo.  The highest wind gust measured at Rick Husband International Airport was 69 mph and occurred at 2:53 a.m.  Arguably, the most impressive aspect of this event was that severe wind gusts (58 mph or greater) occurred continuously for almost an hour between about 2:50 a.m. and 3:45 a.m.! 

With a sustained period of winds this strong, it is no surprise that some damage occurred.  In fact, 7 miles north northeast of Amarillo, part of a roof was blown off a house, which led to broken windows in surrounding homes.  A metal outbuilding was also blown over a fence about 6 miles east northeast of Amarillo on the south side of Highway 60.  Another report of roof damage occurred to a residential structure about 3 miles northeast of Amarillo.  A local business also suffered garage door damage about 1 mile northeast of Amarillo. Most interesting, the strong winds were also responsible for setting off several security alarms around town.

It has been preliminarily concluded that a wake low was likely responsible for these severe wind gusts.  Wake lows typically occur within the stratiform region of a complex of storms.  Within this area, rain continues to fall, which may result in evaporational cooling, thereby reducing the air temperature.  However, a few thousand feet above the surface, a rear inflow jet associated with a convective complex begins to descend toward the ground.  As air descends, it warms due to decreasing volume.  Despite the fact that evaporational cooling may be occurring with the precipitation, it cannot compensate for the warming induced by the descending air.  As a result, low-level temperatures warm, dew points drop, a pronounced pressure gradient develops, and wind speeds increase.

Temperature, dew point, relative humidity, and pressure time series     Wind speed, wind gust, and pressure time series

Temperature, dewpoint, relative
humidity, and altimeter time
series.

    Wind speed, wind gust,
and altimeter time series.

The images above show these changes graphically over the course of about 9 hours.  As the strongest storms moved over Amarillo between 1:10 a.m. and 1:40 a.m., evaporational cooling caused the temperature to decrease and the dew point to increase, which increased the relative humidity.  However, shortly after 2:00 a.m., the stratiform precipitation region moved over Amarillo, and the temperature began to rise while the dew point began to drop, thus lowering the relative humidity.  This general trend continued for the next few of hours.  The altimeter measures the pressure in inches of mercury.  A substantial decrease in pressure was observed between about 2:10 a.m. and 3:40 a.m. along with a corresponding increase in sustained wind speeds and wind gusts.

 

Radar image    
2:47 a.m. base velocity image
Base reflectivity at 2:39 a.m.     Base velocity at 2:47 a.m.

Radar reflectivity at 2:39 a.m. showed the strongest storms extending from southeastern Armstrong County northward to near Pampa.  Meanwhile, a region of stratiform rain extended westward behind the strongest convection.  It is in this stratiform precipitation region that the wake low developed.  The enhanced pressure gradient associated with the wake low was responsible for the strong wind speeds observed on the base velocity image at 2:47 a.m.  This image indicated severe winds less than 300 feet above radar level east northeast of Amarillo.  It was in this area that some wind damage occurred.  Wind speeds closer to the city of Amarillo were likely much stronger than indicated on the radar image.  The orientation of the wind direction relative to the radar was in a manner such that the actual wind speed was grossly underestimated.

We would like to thank Steve Cobb, Science and Operations Officer at NWS Lubbock, for providing the 5-minute graphs.


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