On 12 April 2022, at 1800 UTC, a mid-latitude surface cyclone was present in the central US centered over Nebraska, Colorado and Kansas. At this time, observations showed the system reaching pressures as low as 986 mb over Nebraska. Multiple fronts were present extending outward from the center of the surface cyclone. These included a strong cold frontal boundary which extended southwest down through Arizona, and a warm front which extended eastward through the Ohio Valley. There was also a dry line present which extended from near the low-pressure center southward all the way down through southern Texas (Fig 1).
Figure 1: Surface Analysis on 12 April 1800 UTC
At this time, the surface cyclone was centered downstream a well-developed upper-level trough. At 1800 UTC, radar imagery showed there was low levels of precipitation present along the aforementioned cold front in regions of western Nebraska and eastern Colorado. Additionally, there was moderate levels of precipitation present in the northern states of the Dakotas, Minnesota, and Michigan. At this time, most of this precipitation was occurring in the form of snow which could be assessed due to the reflectivity appearing “smoothed out” with less definition. Moderate to heavy levels of precipitation can be observed occurring in central Texas along the dry line present (Fig 2).
Figure 2: Radar imagery showing base reflectivity from 12 April 1800 UTC – 13 April 0200 UTC
From 1800-0200 UTC, mid-level water vapor imagery shows a dry line moving eastward from central to eastern Texas. On this figure (Figure 3), the dry line can be identified as the dividing line between the dryer body of air to the west (yellow) and the moister body of air to the east (blue and white). To the east of this line, storm cells can be observed forming and strengthening as the dry line moves east during this time period (Fig 2). Additionally, infrared imagery shows convection occurring in this region as cloud top temperatures can be observed shifting to much colder temperatures in a short period of time (Fig 4). This convective activity is a result of dry line dynamics. As the dry, more-dense body of air moves east, it wedges underneath the moist, less-dense body of air to the west producing a lifting mechanism. As the dry line continues moving east, single-cell storms can be observed strengthening into super cells and multicellular storms.
Figure 3: Mid-level water vapor imagery from 12 April 1800 UTC – 13 April 0200 UTC (note: snapshot shown above since .gif file too large to upload to blog website)
Figure 4: Long-wave infrared imagery from 12 April 1800 UTC – 13 April 0200 UTC (note: snapshot shown above since .gif file too large to upload to blog website)
At 2200 UTC 12 April, infrared imagery shows convective initiation occurring in western Iowa as cloud top temperatures drop rapidly. Cloud top temperatures can be used to identify convection because the rapid drop in temperatures represent strong upward vertical motion of moist air. The drop in temperature is a direct result of these upward vertical motions because the cloud temperatures become much colder as the clouds rise in the atmosphere. From 2200-0200 UTC, a large amount of additional convection can be observed occurring from southern Minnesota all the way south through Kansas. The convection is a result of the eastward moving cold front producing a strong lifting mechanism as it forces the warmer air to the east upward. A really cool view of this convection can be observed on night-time microphysics imagery which shows the convection in red color filled with many yellow spots. On night-time microphysics imagery, this type of color pattern represents high, thick, very cold clouds. As previously mentioned, the formation of these thick and cold clouds is evidence of convection as these clouds push higher up into the atmosphere. Another interesting feature which can be observed is the black color outlining the red and yellow feature. The black color represents high, thin clouds which occur as a result of the formation of anvil clouds (Figure 5). Anvil-shaped clouds form due to rising clouds hitting the tropopause boundary which clouds can not push past. As air continues to rise, the cloud tops begin to push outward causing the clouds to take on the shape of an anvil. This is further evidence of the high-levels of convection occurring during this time period.
Figure 5: Night-time microphysics imagery from 12 April 1800 UTC – 13 April 0200 UTC (note: snapshot shown above since .gif file too large to upload to blog website)