_______________________
Corresponding author address: Dr. Charles A. Doswell III, National Severe Storms Laboratory, 1313 Halley Circle, Norman, OK 73069. E-mail: doswell@nssl.noaa.gov
The case of 7 June 1998 in eastern New Mexico and western
Texas is used to illustrate the negative effects on the tornadic
potential associated with a particular synoptic situation created by
a mesoscale region of cloud-covered cool air that was associated with
early thunderstorms. Although the synoptic situation exhibited many
of the features of a significant tornado episode, only two relatively
brief and weak tornadoes were reported, despite the presence of a
long-lasting supercell that produced a long swath of giant hail. In
this case, the development of thunderstorms early in the day
maintained cloudiness that inhibited the destabilization of the
surface-based airmass over which the afternoon thunderstorms moved.
The long-lasting supercell overrode this mesoscale region and was
able to persist as an elevated supercell despite the surface-based
airmass stability, but its tornadic potential was apparently
terminated by its interaction with this mesoscale feature.
Implications for operational forecasting and warnings are discussed.
When considering the role of mesoscale processes related to some severe weather event, most authors have focused on how mesoscale processes contribute to an enhancement of the severe weather potential. There can be no doubt that such enhancements occur (see, e.g., Magor 1959; Doswell 1987; Rockwood and Maddox 1988; Rasmussen et al., 2000), but this is not a complete picture of the role played by mesoscale processes. In fact, within our experience, the most common impact of mesoscale events is to have an inhibiting effect on the chances for severe convection.
In the following study, a case example is used to illustrate the negative impacts associated with a mesoscale process on the severe weather potential of subsequent deep moist convection. Often, when convective outflows reach mesoscale proportions, they act to prevent further deep, moist convective storms. For this particular case, however, the result of early convection was not total suppression of convection developing later in the day, but rather the inhibition of its tornado potential. It is not our intent to provide a comprehensive review of the full range of possibilities inherent in mesoscale features. Rather, the example we consider illustrates that an operational diagnosis of atmospheric processes, including those at the mesoscale whenever possible, should not focus exclusively on those aspects favorable to a particular outcome. A complete diagnosis should also include due consideration to those mesoscale aspects of a forecast situation that are unfavorable to a particular event's occurrence.
Section 2 gives a synoptic-scale overview of the situation on the morning of 7 June 1998 in eastern New Mexico and western Texas, focusing on the severe weather potential implied at 1200 UTC. Then, in section 3, a detailed surface analysis is combined with satellite imagery and soundings to describe the characteristics of a mesoscale region of clouds and outflow that developed during the day of 7 June. It is shown that this mesoscale area of clouds and outflow represented a surface-based layer of relatively high static stability. In section 4, a description of convective evolution reveals the unmistakable influence of that mesoscale region. Finally, some discussion and conclusions are presented in section 5.
The pattern at 1200 UTC shows a strong short wave trough at 500 hPa in the southwestern United States (Fig. 1). In the layer from 700 to 500 hPa, a region of high lapse rates (implied by the 700-500 hPa temperature difference) was being advected over the plains in the southwesterly flow ahead of the shortwave trough (Fig. 2). Surface flow at this time is still being influenced by the recent passage of the surface high pressure, having a large easterly component over Texas, becoming strongly southerly in northern Oklahoma and the Texas panhandle (Fig. 3). Surface dewpoints are not extremely high over the Plains for this late in the spring, but the setting seems primed to begin a rapid moisture return.
The morning outlook for severe thunderstorms from the National Weather Service's Storm Prediction Center (hereafter, SPC), issued at 1523 UTC said about eastern New Mexico and far western Texas:
The morning raobs show that rich Gulf moisture ... with boundary layer mixing ratios approaching 15 g kg-1 ... which had been shunted southward into eastern New Mexico during the last 48 h is now rapidly returning northwestward through the Rio Grande valley into far western Texas and eastern New Mexico. Surface dewpoints in the upper 50s to low 60s should extend as far north as Amarillo/Tucumcari by late afternoon.[1]
That outlook's discussion described the synoptic situation in the following terms:
Active pattern over the central and southern Plains this period as upper low and associated speed maximum now over the southern Great Basin shear east-northeastward across the southern/central Rockies. At the surface ... low now over southern Utah should give way to stronger cyclogenesis in the lee of the Colorado Rockies by early this afternoon. The Colorado low should then track east-northeastward along developing warm front into southern Nebraska later tonight/early Monday.
On this basis, the lead SPC forecaster issued an outlook calling for a "slight risk" of severe thunderstorms in the region shown in Fig. 4, which included eastern New Mexico and far western Texas (hereafter, the "threat area").
For the remainder of the day, the threat area remained underthe same "slight risk" threat assessment through several updates to the SPC outlook. By 0000 UTC that evening, the synoptic pattern had evolved more or less as expected. At 500 hPa (Fig. 5), the short wave trough was moving east-northeastward, displacing the ridge over the area at 1200 UTC, and bringing strong southwesterly winds aloft across the threat area. High mid-tropospheric lapse rates (as shown by the 700-500 hPa temperature difference field in Fig. 6) had not moved very far eastward, however, with the main axis running slightly west of the Continental Divide through New Mexico and into Colorado. At 850 hPa (Fig. 7), a lee cyclone had indeed developed, with a strong southerly current arising over the lower Rio Grande River valley and extending into western Kansas, in response to that cyclogenesis.
At the surface, the pattern in the threat area was rather complex, with surface cyclones in Colorado and New Mexico developing in the lee of the Rocky Mountains, apparently in response to the approaching short wave trough. We will be elaborating on the details of this evolution in section 3, but a strong dryline had formed in eastern New Mexico, not far west of the Texas border by this time (Fig. 8). While surface dewpoint values in the southern part of the threat area had increased in the 12 h since 1200 UTC (cf. Fig. 3), temperatures in western Texas had not increased as much as those in southeastern New Mexico.
From this synoptic-scale perspective, the situation looked promising for the development of tornadic supercells, even though the potential was short of that associated with a major outbreak of tornadoes (as described in Doswell et al. 1993). Simply by looking at the analyzed weather charts for this case, we concur with the outlook: tornadic supercells were a noteworthy possibility in the threat area. Even for "synoptically evident" cases (Doswell et al. 1993), however, the actual evolution of events can be strongly dependent on the mesoscale details. Figure 8 indicates some important mesoscale complexity, so we will consider this in more detail in the next section.
Given that the operational surface data have an average distance to their nearest neighbor on the order of 100 km, it is possible to do a "subsynoptic" scale analysis of them, especially when considering the hour-by-hour changes, to infer the mesoscale structure with some limited confidence. Confidence in the analysis can be substantially improved by combining satellite imagery with the surface data.[2]
At 1402 UTC (Fig. 9), the visible image reveals an extensive area of mixed low and high clouds over the threat area, extending southeastward to near the Gulf of Mexico. Relatively clear skies prevailed that morning over north Texas, most of Oklahoma, and the eastern Texas Panhandle. By late morning (1702 UTC; Fig. 10), however, thunderstorms developed in far western Texas, northward from near Midland into the western Panhandle.
As can be seen in the surface data at 1800 UTC (Fig. 11), this thunderstorm activity produced surface outflow and maintained cloudy skies over the affected region. A region of cool temperatures was centered in the northwestern Texas Panhandle, extending eastward to near the Oklahoma border and southward to south of Lubbock, Texas.
By 2115 UTC, the thunderstorm activity had consolidated into three complexes: one leaving the extreme northeastern Texas Panhandle, a second area of thunderstorms along the southeastern portion of the Texas Panhandle, and the third moving into north Texas (Fig. 12). Considerable cloudiness persisted over most of the far west Texas part of the threat area, with only scattered high and low clouds in most of eastern New Mexico. The associated 2100 UTC surface analysis (Fig. 13) reveals the persistent cool temperatures under the cloud cover in far west Texas, The continuing cloudiness there was reducing the insolation that would warm the near-surface temperatures, in comparison to those in southeastern New Mexico.
As shown in the WSR-88D vertical wind profile from the Cannon Air Force Base, New Mexico radar (Fig 14), at this time, the threat area had a wind profile with considerable vertical wind shear, including notable veering in the layer just above the surface. It is well-known that such a wind profile is favorable for supercells and possible tornadoes (Moller et al. 1994).
A comparison between the 0000 UTC soundings at Amarillo (AMA) and Midland (MAF), Texas is also revealing (Fig. 15). Unfortunately, the absence of a sounding in eastern New Mexico precludes knowing what the surface-based instability was ahead of the thunderstorms that developed there on that afternoon. The Amarillo sounding was within the cool, cloudy airmass left behind in the wake of the early-developing thunderstorms, whereas the Midland sounding was within a relatively warm, moist airmass (cf. Fig. 8), although it was not as warm as in southeastern New Mexico. The AMA sounding was about 5C colder than the MAF sounding from the surface to about 600 hPa. From the surface values of temperature and dewpoint reported in each sounding, the 0000 UTC surface wet-bulb potential temperature (qw) at AMA was about 20C, whereas that at MAF was roughly 23.5C. In southeastern New Mexico, in the narrow band of warm, moist air, surface values of qw were as high as 25C at 2300 UTC (not shown). Although there apparently is a small amount of convective available potential energy (CAPE) associated with the surface parcel in the AMA sounding (~500 J kg-1), there is considerable convective inhibition (CIN) associated with that parcel's ascent curve (~200 J kg-1). On the other hand, considerable CAPE (~2500 J kg-1) is found in the surface parcel for the MAF sounding, with little or no CIN. Thus, an analysis of soundings based on the surface parcels from these two locations gave very different indications of the surface-based instability, as confirmed in Fig. 15.
Three hours later, at 0015 UTC, two of the three initial thunderstorm complexes remained active; one along the Kansas-Oklahoma border and the other moving through north Texas (Fig. 16). The latter exhibited an "enhanced-V" infrared satellite image signature (McCann 1983), but there was no reported severe weather with this storm. However, another major thunderstorm complex had developed, with its active convection at the upstream end of its large anvil in eastern New Mexico, just west of the Texas border. An "enhanced-V" signature was also evident with the southernmost storm in this complex. These thunderstorms had developed around 2200 UTC (not shown) in the High Plains of eastern New Mexico west of Clovis, when the surface dryline was still in the vicinity. Recall the surface analysis (cf. Fig. 8) shows that the thunderstorms at 0000 UTC were located near the surface position of the eastward-advancing dryline. Thus, they were in the narrowing gap between the dryline and the pool of cold, cloudy air left in the wake of the thunderstorms that developed in the late morning. Although the presence of this cool, cloudy air was not completely preventing a return of surface-based moisture, as evidenced by rising dewpoints in the threat area, it was still relatively cool in west Texas. At 0000 UTC it is relatively late in the day, limiting the chances for further destabilization by insolation.
By 0200 UTC, the thunderstorm that developed on the High Plains of New Mexico was moving across western Texas. Infrared satellite imagery (at 0202 UTC on 8 June; Fig. 17) shows that this storm continued to exhibit an "enhanced-V" signature. Note that the storm in northern Texas that earlier had also shown a similar signature was apparently decreasing in intensity; the signature was no longer present. It can be seen from the 0300 UTC surface analysis (Fig. 18) that the surface-based airmass over which the storm in the Texas Panhandle was moving was still relatively cool.
Therefore, it appears the thunderstorms that developed during the late morning in western Texas caused the surface-based airmass in the threat area to remain relatively cool, cloudy, and with much reduced instability over what might have been anticipated from the synoptic evolution. By maintaining this subsynoptic region of cool, relatively stable air at the surface, the thunderstorms and their associated outflow apparently created an inhibiting mesoscale structure. That is, the persistence of a mesoscale area of cloudiness and outflow was preventing the evolution of unstable conditions at the surface, despite an apparently favorable synoptic pattern. Next, we need to consider just what happened on the storm-scale events, to see how this mesoscale feature influenced the weather.
The National Weather Service's operational network of WSR-88D Doppler radars provides a reasonably detailed picture of the character of the convection on this day. As shown in Fig 19, the nearest WSR-88D radar (at Cannon Air Force Base, NM [KFDX]) is relatively close to the events in Clovis, New Mexico, although that in Lubbock, TX (KLBB) is rather distant from the storms. At 2205 UTC (Fig. 20), there were two strong storms in eastern New Mexico, as depicted by KFDX radar, the northernmost of which was more mature and displayed an operational algorithm-detectable mesocyclone [see Zrnic´ et al (1985)]. By 2232 UTC (not shown), both storms were showing mesocyclone signatures and at 2323 UTC (Fig. 21), the northernmost storm was beginning to decay, while the southernmost storm was approaching Clovis. The presence of persistent WSR-88D algorithm-detectable mesocyclones and the low-level reflectivity morphology make it pretty clear that both storms had become supercells; see Doswell and Burgess (1993) for a discussion of the observable characteristics associated with supercells. The WSR-88D image of the storm at 0017 UTC is notable for its obvious supercellular character (Fig. 22).
The northern storm continued its decline, but the southern storm maintained its supercell characteristics across the northern parts of Clovis, New Mexico and on into Texas. At 0037 UTC, the KLBB radar revealed a bounded weak echo region (Fig. 23), indicative of continuing supercell characteristics for the storm. Further evidence for the continuing supercellular character can be found in the low-level reflectivity (Fig. 24a) and radial velocity structure (Fig. 24b). An hour later, at 0136 UTC, the storm maintained its supercell characteristics (not shown), and this was still so at 0237 UTC (Fig. 25a, Fig 25b). After 0237, the storm began gradually to decay.
The path of this storm across Curry County in New Mexico, as well as Parmer, Castro, and Swisher Counties in Texas included several reports of severe weather (Fig. 26), mostly large hail (up to 4.5 inches in diameter in Castro County, TX). Notably, the tornadoes associated with this supercell occurred in Curry County, New Mexico. In spite of having supercell characteristics for many hours, the storm became tornadic only briefly, but went on to produce large hail for several hours thereafter.
The surface analyses show that during its tornadic phase, the supercell was approaching the western periphery of the cloudy, relatively cool air that had been left behind in the wake of the deep convection that had developed early in Texas. It appears that the supercell storm eventually overrode this pool of surface-based cool, relatively stable air shortly after producing its second tornado on the outskirts of Clovis, NM, becoming an "elevated" supercell storm. Rasmussen et al. (2000) document that storms encountering old outflow boundaries sometimes may have enhanced tornadic potential. However, unlike the 02 June 1995 case presented by Rasmussen et al., the pool of cloudy air the supercell encountered on 07 June 1998 was cool and stable, rather than showing high qw values as a result of modification by solar heating. The 0000 UTC soundings at AMA and MAF confirm the relative stability of the two airmasses. If the surface air at MAF (with a qw of ~23.5C) is lifted over the cool pool, of course, it exhibits considerable CAPE (~2500 J kg-1), depending somewhat on the sounding to which the parcel ascent curve is compared.[3]
The early deep convection produced outflow that maintained the cool temperatures and the outflow region remained mostly cloudy all afternoon. Therefore, only a narrow zone of surface-based moist, unstable air was present between the approaching dryline and the mesoscale cold pool created by the cloudiness and early storms. It was within this narrow zone that the supercell became tornadic. The development of the southern supercell storm probably contributed to the relatively early demise of the northern supercell, by intercepting the northward flow of surface-based instability. Once the single remaining supercell moved across the narrow region where conditions were most favorable for tornadoes, it encountered cool, stable air at the surface and the tornadic potential dropped dramatically, as discussed by Maddox et al. (1980). However, it appears that the environment continued to be favorable for supercells above the surface-based, mesoscale cool pool, so the now-elevated supercell continued to produce copious amounts of hail (including giant hail). Note that the surface-based cool air also apparently limited the strong surface wind gust potential for this storm; the only reported severe wind gust occurred in southeastern Curry County in New Mexico. Any strong downdrafts created by the supercell were apparently unable to penetrate to the surface through the strongly stable mesoscale cool pool.
Although it is not possible to know what might have happened had the early storms not developed in the Texas Panhandle, it certainly appears that a situation with considerable potential for tornadic supercells was changed by the mesoscale cool pool maintained by the early storms. In this case, the cool pool did not prevent the supercell (which became elevated after encountering the cool pool) from continuing to produce large hail for several hours, but it apparently reduced the tornado potential to a narrow zone between the dryline and the cool pool.
Forecasters certainly need to maintain vigilant diagnostic procedures to be aware of the changing mesoscale circumstances. In this case, even at its lowest elevation angle (0.5°), the KLBB radar beam overshot the cool pool for most, if not all, of the storm's passage across it. Therefore, the appearance of the storm on the WSR-88D continued to look potentially tornadic even though the actual tornadic potential is considerably reduced. One of us (DVB) was working in the Lubbock, Texas, National Weather Service office that evening. Tornado warnings for the storm were maintained as it moved across all of Parmer county, even though spotters did not report any tornadoes. At that point, however, the office staff realized the elevated character of the storm and dropped the tornado warnings while continuing severe thunderstorm warnings. The challenge during the evening had been to recognize the nature of the boundary the storm had crossed, and the change in stability associated with it. The western boundary of the mesoscale cool pool never exhibited much of a windshift, which would have been an obvious clue to the presence of a boundary.
In becoming an elevated supercell, its inflow was forced to overide the cool air, but the mesoscale cool pool reduced the likelihood that any vortex would penetrate to the surface. One of us (CAD) chased this storm, and there was a classic rear-flank downdraft "clear slot" (Moller et al. 1974), but there was no visual evidence for surface-based inflow into a "wall cloud" structure during the passage of the storm across Parmer and Castro Counties in Texas. The convective towers of the storm were not visible owing to stratiform overcast, and the storm appeared only as a darkening of the stratiform cloud base, with the "clear slot" being the only visual evidence of the storm's supercell character.
Given the problems with recognizing the character of the situation from radar alone, forecasters having the responsibility for issuing warnings would need to be aware of the changing environment for this storm as it moved into Texas. The limits of any radar to detect the important features of this storm near the surface make this a challenging situation. Moreover, surface data alone do not necessarily mean that the cool pool is both deep and notably stable. The 0000 UTC soundings at MAF and AMA do reveal the character of the airmasses rather well, but 0000 UTC sounding data would arrive well into what had been a challenging situation for issuing warnings. A well-trained storm spotter (see Doswell et al. 1999) might have recognized the elevated nature of the storm and been able to inform the forecasters of the situation. Storm spotter input is most helpful when (a) the forecaster has maintained "situation awareness" through continuous mesoscale diagnosis, (b) forecasters are knowledgeable about the potential for severe weather revealed by storm (in this case, the elevated character of the supercell), and (c) storm spotters are well-trained in recognizing salient features of the storms they are seeing.
Acknowledgments. The authors appreciate the help provided in producing figures from Loretta McKibben and Vikki Farmer. Rich Thompson, Roger Edwards, and Matt Wandishin provided helpful comments on an early version of the manuscript that greatly improved the presentation.
______, and D.W. Burgess, 1993: Tornadoes and tornadic storms: A review of conceptual models. The Tornado: Its Structure, Dynamics, Hazards, and Prediction (Geophys. Monogr. 79) (C. Church, D. Burgess, C. Doswell, and R. Davies-Jones, Eds.), Amer. Geophys. Union, 161-172.
______, R.H. Johns and S.J. Weiss, 1993: Tornado forecasting: A review (Invited paper). The Tornado: Its Structure, Dynamics, Hazards, and Prediction (Geophys. Monogr. 79) (C. Church, D. Burgess, C. Doswell, and R. Davies-Jones, Eds.), Amer. Geophys. Union, 557-571.
______, A.R. Moller and H.E. Brooks, 1999: Storm spotting and public awareness since the first tornado forecasts of 1948. Wea. Forecasting, 14, 544-557.
Maddox, R.A., L.R. Hoxit and C.F. Chappell, 1980: A study of tornadic thunderstorm interactions with thermal boundaries. Mon. Wea. Rev., 108, 322-336.
Magor, B.W., 1959: Meso-analysis: Some operational analysis techniques utilized in tornado forecasting. Bull. Amer. Meteor. Soc., 40, 499-511.
McCann, D.W., 1983: The enhanced-V, a satellite observable severe storm signature. Mon. Wea. Rev., 111, 887-894.
Moller, A., C. Doswell, J. McGinley, S. Tegtmeier and R. Zipser (1974): Field observations of the Union City tornado in Oklahoma. Weatherwise, 27, 68-79.
______, M.P. Foster, C.A. Doswell III and G.R. Woodall (1994): A supercell thunderstorm spectrum and its application in the operational environment. Wea. Forecasting, 8, 327-347.
Rasmussen, E.N., S. Richardson, J.M. Straka, P.M. Markowski and D.O. Blanchard, 2000: The association of significant tornadoes with a baroclinic boundary on 2 June 1995. Mon. Wea. Rev., 128, 174-191.
Rockwood, A.A., and R.A. Maddox 1988: Mesoscale and synoptic scale interactions leading to intense convection: The case of 7 June 1982. Wea. Forecasting, 3, 51-68.
Zrnic´ , D.S., D.W. Burgess, and L.D. Hennington, 1985: Automatic detection of mesocyclonic shear with Doppler radar. J. Atmos. Oceanic Technol., 2, 425-438.
Figure 2. Analysis of features at 700 hPa, 1200 UTC on 07 June 1998, showing isohypses (heavy solid lines, contoured at 3 dam intervals), 700-500 hPa temperature difference (heavy gray lines, contoured at 2C intervals), and isotherms (light gray lines, contoured at 2C intervals, beginning at 0ºC. Station model is same as Fig. 1, except the 700-500 hPa temperature difference is plotted in the lower right.
Figure 3. Regional surface analysis at 1200 UTC on 07 June 1998, showing isobars (heavy solid lines, contoured at 2 hPa intervals), isotherms (thin gray lines, contoured at 5F intervals), and isodrosotherms (heavy gray lines, contoured at 10F intervals, beginning at 40ºF). A thermal ridge is denoted by the heavy, finely-hatched light gray line, and a dewpoint ridge by the heavy, coarsely-hatched gray line. The station plot model is conventional.
Figure 4. Map showing the Storm Prediction Center (SPC) Convective Outlook product issued at 1523 UTC.
Figure 5. As in Fig. 1, except for 0000 UTC on 08 June 1998; 12-h height changes (dam) have been added to the station model, in the lower right.
Figure 6. As in Fig. 2, except for 0000 UTC on 08 June 1998.
Figure 7. Analysis of features at 850 hPa, 0000 UTC on 08 June 1998, showing isohypses (heavy solid lines, contoured at 3 dam intervals). The scalloped line denotes the dryline, the dashed line denotes a geopotential trough, and frontal symbols are conventional. A heavy solid line with an arrowhead denotes the low-level jetstream axis. Station plots show temperature (ºC) in the upper left, dewpoint depression (ºC) in the lower left, geopotential height (dam) in the upper right.
Figure 8. As in Fig. 3, except for 0000 UTC on 08 June 1998; the scalloped line denotes the dryline, heavy stippled lines denote thermal boundaries, dashed lines denote troughs.
Figure 9. Visible satellite image at 1402 UTC, 07 June 1998.
Figure 10. As in Fig. 9, except for 1702 UTC.
Figure 11. As in Fig. 8, except for 1800 UTC; dryline denoted by heavy hatched line.
Figure 12. As in Fig. 9, except for 2115 UTC.
Figure 13. As in Fig. 11, except for 2100 UTC.
Figure 14. Time section of vertical wind profile from the Cannon Air Force Base, NM WSR-88D radar, with UTC time indicated at the bottom, increasing to the right. Heights in thousands of feet are shown on the left. Wind barbs follow the National Weather Service operational convention, in knots; "ND" indicates no data
Figure 15. Skew-T, log p plots of Amarillo, Texas (AMA; in blue) and Midland, Texas (MAF; in red) soundings at 0000 UTC on 08 June 1998; lifted parcel ascent curves shown include the virtual temperature correction. Isobars (thin solid lines) are labeled in hPa, and isotherms (thin dashed lines) and isentropes (curved thin solid lines) are both labeled in deg C.
Figure 16. False color-enhanced infrared satellite image at 0015 UTC, 08 June 1998. Dark greens indicate the coldest cloud top infrared temperatures.
Figure 17. As in Fig. 16, except at 0202 UTC.
Figure 18. As in Fig. 8, except for 0300 UTC.
Figure 19. Map showing the location of Albuquerque, NM (ABQ), Cannon Air Force Base, NM (KFDX), and Lubbock, TX (KLBB) WSR-88D radars, as well as Clovis, NM, superimposed on the county boundaries (and names) in gray.
Figure 20. As in Fig. 19, except at 2332 UTC.
Figure 21. As in Fig. 20, except at 2332 UTC.
Figure 22. As in Fig. 20, except a close-up view at 0017 UTC.
Figure 23. WSR-88D cross section of the supercell at 0037 UTC, as seen on the Lubbock, TX (KLBB) radar, showing reflectivity structure.
Figure 24. KLBB view of (Fig. 24a) reflectivity (dBz) and (Fig. 24b) storm-relative radial velocity at 0036 UTC on 08 June 1998, at 0.5º tilt.
Figure 25. As in Fig. 24, except at 0237 UTC [Fig. 25a; Fig. 25b]
Figure 26. Map of the reported severe weather, with "H" denoting a hail report (diameter given in inches), "W" denoting a wind report (speed given in knots), and "T" denoting a tornado (F-scale given).
