An active period of severe weather struck the central/southern plains from late April through the first third May 2024. In this blog post, we’ll investigate the April 30 event over the southern plains.
On April 30, a narrow line of severe thunderstorms developed from Texas through Iowa. Early signs of convective initiation along a dryline were analyzed in GOES imagery by SPC forecasters, discussed in Mesoscale Discussions at 1935 UTC and 2024 UTC. Figure 1 shows the MD graphics, which include annotation on the Visible satellite imagery at the time.
Early convective development along the dryline is shown in 1-min Day Cloud Phase Distinction RGB Imagery. From 1745 UTC – 1844 UTC, cu growth is observed over southwest OK, with the best vertical growth, beginnings of glaciation, and an orphan anvil, highlighted at the end of the period, where we expected CI to be most likely in the next hour or so (Fig 2).
Figure 2: 30 April 2024 GOES-East 1-min Day Cloud Phase Distinction RGB Imagery.
Over the following hour, we observe convective initiation from the region of cu that was highlighted in Fig 2 (Fig 3). During the same period (through 1945 UTC), we diagnose another potential are of CI to the southwest of the first area, where the cu are becoming more agitated and orphan anvils appear.
Figure 3: 30 April 2024 GOES-East 1-min Day Cloud Phase Distinction RGB Imagery.
Over the next hour (to 2055 UTC), the first area of convection continues to develop, while a few thunderstorms initiate from the second area (Fig 4).
Figure 4: 30 April 2024 GOES-East 1-min Day Cloud Phase Distinction RGB Imagery.
The two GOES-East Meso Sectors had a partial overlap over Oklahoma and Kansas, allowing for 30-second imagery in the overlap region. Figure 5 shows a zoomed out view of the two meso sectors (which have their 1-min update offset by 30-seconds). Where the sectors overlap, 30-second imagery is available. AWIPS can be configured to show the 30-second partial-meso-overlap imagery.
Figure 5: 30 April 2024 GOES-East Meso-1 and Meso-2. In the animation, each meso sector updates every 1-minute, with an offset of 30-seconds.
Focusing on the 30-second imagery region after the convection matured, a VIS/IR sandwich animation captures the storm top features well by combining the texture details from the high resolution VIS with the qualitative temperature details from the IR. While there is a Sandwich RGB in awips, one can also create their own sandwich manually, allowing for more customization. The example in Figure 6 is a manual Sandwich that uses custom colormaps. Apparent in the imagery are storms with large, cold and persistent overshooting tops, long-lived above anvil cirrus plumes, and rapid anvil expansion with crisp edges. The northern storm in the pair eventually dissipates (loss of storm top texture, OT, AACP), while the southern storm thrives.
Figure 6: 30 April 2024 GOES-East 30-second VIS/IR Sandwich Imagery.
Another area of severe storms had developed in north Texas. Viewing 1-min VIS, we see the rapid development of OTs and AACPS. However, we note convective decay when those features become lost, along with an overall loss of texture at the storm top (Fig 7).
Figure 7: 30 April 2024 GOES-East 1-min VIS Imagery.
After dark, we must rely on IR imagery to assess convective decay. Focusing on a convective complex over southern Oklahoma, we note persistent OTs, and gravity waves emanating outward from them, prior to 0530 UTC (Fig 8). Between 0530 UTC and 0630 UTC, we note a disappearance of the OTs and associated gravity waves. Thereafter, the overall complex experiences a gradual warming.
Figure 8: 30 April 2024 GOES-East 1-min IR Imagery.
Similar to with the DCPD RGB during the day, the Nighttime Mcirophsyics RGB can be leveraged to identify early signs of CI overnight. Low level liquid clouds, appearing as light blue/cyan, will transition to a light green/yellow/orange with glaciation and early cooling. Those clouds will transition to red with continued glaciation and cooling. That process can be seen in the two-hour long 1-min Nighttime Microphsycis RGB animation in Fig 9, as convection develops on the western edge of a mature convective system. In the animation, IR imagery is overlaid for cold brightness temperatures in order to capture storm top features, since the NightMicro doesn’t’ provide usable information in this area.
Figure 9: 30 April 2024 GOES-East 1-min Nighttime Microphysics + IR Imagery.
Taking a broader look at the region, and loading the GOES CAPE product with an IR (grayscale) underlay, we observe convective development in the context of the GOES derived thermodynamic field. As discussed previously, there is value in the GOES derived thermo products in capturing trends in the fields, as well as in depicting the position of horizontal gradients. In this case, we see instability increase within a narrow corridor through the morning and early afternoon, in addition to a tight gradient on the western edge of the instability (the dryline). It is along the gradient in instability, as depicted in the GOES product, that we see convection develop from Texas through Iowa.
Figure 10: 30 April 2024 GOES-East 5-min CAPE + IR Imagery.
Bill Line, NESDIS/STAR
