Throughout the morning on the 26th of October 2021 storm conditions developed throughout the Great Plains region of the US. A midlatitude bomb cyclone was present in the Eastern Pacific off the Washington State Coast and brought heavy precipitation to the West Coast throughout the day on Monday. As the associated low-pressure system was carried eastward onto land by the jet stream throughout the latter half of Monday the 25th of October and into Tuesday, upward vertical motion over the lower midlatitudes were played a part in the convective activity explaining heavy precipitation which developed over the Great Plains on Tuesday. Diverging winds are characteristic along the downwind side of a western trough and are responsible for lowering pressures and acting as a lifting mechanism for parcels of air to cool and create stormy conditions and increased wind speeds.
Figure 1. shows windspeeds and vertical motions at 300 mb present on 1200 UTC 26 October 2021.
The rising air from this divergence could explain the convective event which stirred up over the Colorado – Wyoming, Wyoming – Nebraska – South Dakota boarders as seen in figure 2 as lapse rates between 700 mb to 500 mb increase from 0000 26 October to 0008 26 October. The increase in lapse rate value means that air temperature is falling with the rise in altitude at an increasing rate. When the lapse rate is high in one area with respect to the surrounding locations, there is a greater probability of developing CAPE, a key indicator for the development of a storm system.
Figure 2a.
Figure 2b.
Figure 2a and 2b. show the development of lapse rates over the Great Plains on 0000 UTC 26 October 2021 and 0008 UTC 26 October 2021.
Another observation map can be used to help explain how this storm originated and was carried out by the surface to 6km shear vector values. Along Colorado and Wyoming at 1200 UTC 26th October 2021, there was a shear wind value of 90 knots, which can be seen in figure 3. Higher values for the surface to 6km shear vector map can indicate high wind speeds. For this case there were strong speed shear values and minimal directional shear, however this is still a good indicator for the development of strong winds and convective activity which could lead to storm conditions and tornados.
Figure 3. shows vector shear values (kts) for the surface to 6 km along the continental US. Focusing on the West and Great Plains, a troughlike feature carries strong shear values, representing potential for convective activity, thunderstorms, and strong wind speeds.