On June 5, 2013, Lubbock Texas is hit by a haboob at 10:30 pm. The storm is categorized as a wind event by television media and the dust component goes unreported. This event is used as a case study to evaluate the usefulness of the polarimetric variables differential reflectivity (ZDR) and correlation coefficient (CC) in identifying the storm as a haboob. Photographic evidence of the haboob is collected and correlated to NEXRAD signatures of base reflectivity and velocity from the Lubbock TX NEXRAD station (KLBB). NEXRAD level III products ZDR and CC are also obtained. The storm presents with gust front features to the north and east of the station. Low values returned from CC indicate nonmeteorological content. ZDR representations weakly indicate the presence of gust fronts to the east, with a stronger signal to the north. As no visual evidence of the northern gust front is available, the ZDR data are inconclusive. The correlation of low CC values to the visual representation of the haboob is an indicator that CC in combination with the NEXRAD base reflectivity and velocity products may be used to test wind events for the presence of sand, dust, and dirt and therefore exhibit predictive qualities.
The word haboob is taken from the Arabic habūb meaning “blasting” or “drafting,” and according to Sutton 1925 [
This paper will focus upon these storms: American haboobs, and in particular a single haboob that occurred on June 5, 2013. By the time the storm had hit Lubbock, TX, at 10:30 pm local time, it had become a severe wind event. Local television stations were warning the population about the severity of the oncoming winds, recommending that they take shelter in the innermost part of their home—advice also given to people in advance of an oncoming tornado. What the television reporters never mentioned was the fact that this storm was a haboob. Storm reports were coming in from upwind of the storm with information on wind speed and direction and there were occasional mentions of poor visibility but no mention of the dust component (Fox News Lubbock, Texas, can be heard by clicking the following link:
With the help of the National Weather Service’s Next-Generation Radar Network, severe convective storms can be observed as they develop. As recently as 2010, the NEXRAD network was upgraded and became capable of using polarimetric variables for weather observation. This paper proposes to take a look at NEXRAD data for the Lubbock, TX, storm and to examine the NEXRAD data products: reflectivity (
The following section will give a short background on haboob research. Section
There are few haboob case studies (Sutton 1925 [
A discussion of our direct contact with the storm is as follows. Early in the afternoon of June 5, 2013, the author and the Nimbus Storms Research Lab chase team (Nadia Elfarnawani, Aline Gjelaj, Joey Krastel, and Meredith Robson), while driving north through New Mexico, noticed that our radar was picking up pulse thunderstorms which were developing up in the Santa Fe National Forest. The radar was viewable through an iPhone app called Radarscope, which ingests level III NEXRAD data, maps each variable, and displays it on the phone screen. By 1 pm two storms had distinguished themselves on the radar and were rolling out of the forest descending onto the plateau. By 3:30 pm these storms had intensified as they approached Las Vegas, NM. Migrating east/southeast by 5 : 19 a gust front feature had appeared in the base reflectivity of the National Weather Service (NWS) Weather Surveillance Radar-1988 Doppler located at Cannon Air force Base, Clovis NM (WSR-88D; KFDX). The front was advancing ahead of the thunderstorm. As the storm hit Tucumcari, NM, the weather report announced limited visibility due to haze. As it headed south across Quay County we had just come off the Llano Estacado (palisaded plain) and were entering the valley from the south. We drove several miles on route 209 toward the storm and then stopped. The gust front was clearly visible and tinged with the red Quay County soil. We positioned ourselves close to the advancing storm and then allowed it to chase us back south. By 6 : 19 the haboob was intensifying as it cleared the cap rock (the Llano Estacado). We drove south to the Town of Melrose where we got out for gas and to take more photos. We left Melrose and drove toward Clovis, the storm following close behind. From Clovis we travelled down route 84 to Muleshoe, TX, then on to Littlefield, and finally we arrived in Lubbock at 10:30 pm just as the Haboob was about to roar through. The first rain was blood red. Then the rain cleared as it began to mix with mothball-sized hail. We could barely see as we drove and so pulled off the highway and into a mall parking lot. Joey Krastel videoed the mothball size hail (
Map of route. The map shows the route that the author took going from just south of Tucumcari NM to Lubbock TX. The letters a–f refer to Figure
A methodology was determined by the need to execute two tasks. The first was to assess the storm that was viewed on June 5, 2013, and determine that what was seen was, in fact, a haboob. Given the success of the first task, the second task was to evaluate the NEXRAD radar data products to see whether or not a signature or combination of signatures might be interpreted as identifying the storm as a haboob.
The author encountered the storm at about 4:30 pm in the afternoon coming north off the Llano Estacado in New Mexico into the Quay Valley. We were struck by the approach of what appeared to be a great churning red wave of sand heading south along the valley toward us. We got in front of the storm and proceeded to let it chase us, taking photos periodically until we came to Lubbock TX later that evening. Figure
Photos of Haboob from (a) Route 209, Quay Valley, NM. (b) Llano Estacado, North of Melrose, NM. (c) Melrose, NM. (d) Between Melrose and Clovis, West View. (e) Between Melrose and Clovis, East View. (f) South of Littlefield. Locations may be seen on map in Figure
The Radar Operations Center (ROC) is a part of the National Weather Service and is the home of the Next-Generation Radar or NEXRAD. It was established in 1988 in Norman, OK. The ROC sets up the Weather Surveillance Radar-1988 Doppler or WSR-88D network, which consists of 160 operational, S-band (10 cm wavelength) NEXRAD weather radar systems. In 2010 the ROC began work on upgrading all of the radars to polarimetric capability. Now, besides the ability to record the 0th, first, and second moments, the radars are now capable of emitting both horizontal and vertical radar waves. This enhancement produces the new variables: differential reflectivity, differential phase, and correlation coefficient. Since this paper discusses the haboob in terms of a propagating gust front and its representation via reflectivity, differential reflectivity, base velocity, and correlation coefficient, a short description of each variable is set here.
Reflectivity (
Differential reflectivity is a measure of the log of the ratio of the horizontal to vertical power returns in a pulse volume, which can also be thought of as the log of the ratio of the horizontal reflectivity to vertical reflectivity in linear units, not dBZ units. Its values range from −7.9 to +7.9 in units of decibels (dB):
If the scatterers are round then the ZDR will be zero because the return from both the vertical and horizontal scatterers will be similar. Negative ZDR is infrequent although when encountered it is usually the result of the alignment of ice needles in the presence of lightning. Non meteorological clutter such as birds or insects can also return negative values. A positive ZDR indicates that the range volume contains scatterers aligned horizontally.
Specific to gust fronts or density currents are a change in the direction of the wind with the passage of the front. As discussed by Klingle and Smith 1987 [
Correlation coefficient (CC) speaks to the homogeneity of the scatterers in a range volume. It is a measure of how similarly the horizontal and vertical pulses are behaving within a pulse volume. If the phase angle and magnitude of both the horizontal and vertical pulses behave similarly from time step to time step in the same range volume, CC is 1 or very close to 1. Divergent magnitudes or phase angles return a lower CC. CC can therefore be used to distinguish meteorological hydrometeors from nonmeteorological scatterers such as birds, insects, wind farms, smoke plumes, and chaff. Values for these scatterers tend to be low.
Establishing the presence of a gust front as the cause of the June 5 haboob requires both the NEXRAD reflectivity and velocity signatures. Once established, the polarimetric variables may be read in this light and an attempt to discern a signature specific to haboobs can be made. Klingle and Smith 1987 [
NEXRAD representation of Haboob, June 5, 2013. (a) Base reflectivity. (b) Base velocity. (c) Differential reflectivity (ZDR). (d) Correlation coefficient.
The June 5 Doppler velocity shows linear convergence in the radial along the same thin line regions depicted by the reflectivity. This can be seen also at 8:25 pm local time (CDT) in Figure
There is evidence in the ZDR (Figure
The correlation coefficient (Figure
There is no way to verify that the northern gust front was a haboob because no one was present to witness it. The gust front in advance of the thunderstorm, though, was definitely a haboob and the nonmeteorological signature found in the correlation coefficient is significant.
The importance of forecasting and reporting haboobs lies in the fact that the invasion of dust and particulate matter into the environment causes serious health risks that might be mitigated with enough advanced forecasting. Couple this with the haboob’s capacity to reduce visibility; making transportation extremely dangerous, forecasting these storms becomes imperative. While the June 5, 2013, Lubbock, TX, haboob was a single unreported incident, it is not difficult to make the leap that there have been other storms that have been similarly unreported. Whether this is a widespread problem or not is unclear. Nevertheless, the use of the correlation coefficient in the light of both reflectivity and base velocity can help forecasters visually identify the gust fronts responsible for haboobs and their transport of nonmeteorological materials. This idea opens up many possibilities in regard to future research, in particular, the possibility of developing an algorithm that identifies gust fronts as carriers of sand, dust, or dirt. With identification comes the possibility of identifying historical events and thereby developing a haboob climatology. There is also the possibility that various particulates may have specific ranges in the CC spectrum. It is this author’s wish that this case study might provide information for the improvement and development of the numerical modeling of dust transport for use in operational forecasting.
The author declares that there is no conflict of interests regarding the publication of this paper.
The author would like to thank his program advisors in the past and present, Haydee Salmun of Hunter College, Andrea Molod of University of Maryland, and Jimmy Booth of City College, CUNY, for their extraordinary support in developing this research. The author would also like to thank the Nimbus Storm Research Lab: Nadia Elfarnawani, Aline Gjelaj, Joey Krastel, and Meredith Robson for all their support and their passion for the storm chase.