Strong thunderstorms developing across west Texas on 09 April 2023 resulted in damaging wind gusts and large/accumulating hail. Early satellite analysis by NWS LUB summarizing some of the forcing that would be at play: “Water vapor imagery shows a weak, positively tilted trough working through the forecast area now. An outflow boundary from early morning convection as well as a weak wind shift boundary has been the main focus for convection so far this afternoon.” The aforementioned trough is shown in water vapor imagery in Fig 1, advancing southeast through eastern Colorado, the TX/OK panhandles, and eventually northwest Texas/southern Oklahoma by the end of the period. The trough can be diagnosed in the water vapor imagery by a west/east couplet of warming (drying)/cooling (moistening and clouds).
Mesoscale analysis from the Storm Prediction Center highlighted relevant environmental developments just prior to the development of stronger convection through the analysis of visible satellite imagery: “Visible imagery shows strong heating over the panhandles and into much of the South Plains and northwest TX, the exception being the eastern TX Panhandle into western OK in association with a batch of showers and cirrus. CU is beginning to form within the surface trough from eastern NM into the TX Panhandle, with weak wind convergence.” The SPC MD graphic highlighted these developments in the VIS (Fig 2), and Fig 3 shows the scene in motion.
The mesoscale discussion also mentioned “PS PW sensors show a plume of 0.80-0.90″ PWAT from northwest TX into the eastern TX Panhandle and South Plains”, which supported the GOES-East PW measurements across he region (Fig 4).
Storms developed thereafter, the strongest of which produced large hail and damaging winds as previously mentioned. The storm between Lubbock and Abilene produced a 71 mph wind gust and baseball size hail. Additionally, satellite imagery revealed a long hail swath associated with this storm. In Fig 5, VIS/IR sandwich imagery captures this storm as it intensified over HWY 380 and remained strong as it headed toward and crossed HWY 180 per persistently cold cloud tops and abundant cloud top texture, including overshooting tops and embedded gravity waves. Focusing behind the storm, however, one may notice a trail of static high reflectance at the surface.
To confirm suspicion of a hail swath, we review the corresponding Day Cloud Phase Distinction RGB imagery, which incorporates NIR channel information to differentiate cloud phase but also to diagnose snow/ice cover, as green (Fig 6). Indeed, we see that the trail appears as green, meaning it is highly reflective in the visible channel (considerable green contribution), is not very reflective in the NIR (not much blue contribution), and is relatively warm in the IR, indicating a feature at the surface (not much red contribution). The hail swath is much easier to diagnose in the RGB vs single band imagery.
Given the viewing angle from GOES-East to this location, it is apparent that the storm anvil might be masking the surface in the wake of the storm, to the northwest. Viewing the same scene from GOES-West, one gets a nice view of the backside of this particular storm (Fig 7). Of course, full resolution imagery is not available over this region in AWIPS (aside from FD LWIR), unless there is a meso sector. Forecasters can visit webpages, such as the CIRA SLIDER, to view the full-resolution, full disk imagery anywhere within the full disk. For this case, in my opinion, the hail swath would be confidently and realistically diagnosed in 1-min GOES-East imagery around 2318 UTC. In the GOES-West full disk imagery, one should be able to diagnose the hail swath by 2210 UTC, almost an hour sooner. This extra time could be important to the warning and DSS forecaster in not only confirming that the storm is/was producing hail, but also that it is producing accumulating hail that may negatively impact travel, such as over HWY 180.
Figure 8 provides a four panel comparison with GOES-West on the left and GOES-East on the right, for times of 2210 UTC on top and ~2320 UTC on bottom. Note that while, at 2210 UTC, the hail swath is apparent in GOES-West, it is not detectable in GOES-East. By 2320 UTC, a long hail swath is apparent in GOES-West, while it is first becoming obvious in GOES-East.
Bill Line, NESDIS/STAR