Severe Weather: July 28

9:25 PM Update: Strong inhibition/capping is continuing ahead of the current activity in both North Dakota, and South Dakota. This is currently suppressing, and disorganizing the convection in southern South Dakota. Some cooling is taking place, that may allow the thunderstorms to continue to develop as they move eastward. Still expecting that the thunderstorms will continue into western Minnesota and western Iowa during the overnight hours. The severe weather threat with these thunderstorms is questionable, but still deserves to be watched as we continue through the overnight hours. The timetable for storms entering portions of northwest Iowa looks to be around midnight for extreme northwest Iowa.


9:20 AM Update: A continuing threat of severe weather is likely late this afternoon/evening and into the overnight hours for a portion of the state. Current radar shows lingering thunderstorm activity in southern Iowa this morning, but with weakening trends given strengthening inhibition/capping. Other thunderstorms are ongoing this morning over central North Dakota, which continues to be severe warned for multiple cells. The progression of this MCS is expected to continue east/southeast, with the eventual growth of several individual cells or multicell clusters rather than the previous MCS condition that it was in. Some of this isolated development is already being noted on latest radar trends on the southern periphery of the cluster.

Ahead of this thunderstorm complex, and associated shortwave, clearing skies will allow a warm front to move northward throughout the day. Areas along and south of this warm front will see temperatures rising into the upper 80s and 90s, with dewpoints in the 70s. This will provide a large area of the Dakotas, Nebraska, Minnesota, and Iowa with extreme instability values throughout all levels. Despite this extreme instability, and overall strong lift, thunderstorms shouldn't develop until the later afternoon or evening hours due to strong capping. The most likely areas to be able to breach this strong cap will be along or just ahead of the current cluster and shortwave that is expected to move east/southeast throughout the day. This additional development is likely to occur across the eastern half of South Dakota, as well as southeastern North Dakota where the instability will be present to aid in rapid thunderstorm development. The storms may initially be supercellular in nature, capable of both very large hail, damaging winds, and an isolated tornado given decent shear values and extreme instability.

As the thunderstorms continue into the evening and early overnight hours, expect the evolution into a strong MCS, possible derecho as the storms enter extreme eastern Dakotas, and western Minnesota/Iowa. The tornado threat should decrease, however, the threat for both large hail and damaging winds will continue. The potential for a strong damaging wind threat is there, thus the SPC has issued a moderate risk for portions of the eastern Dakotas, stretching into parts of southwestern Minnesota.

The threat for Iowa should mainly be confined to portions of western Iowa in the early overnight hours. The potential for damaging winds, very large hail, and a potential for a tornado or two is being slated for mainly the northwest quarter of the state. Expect thunderstorm to continue throughout the nighttime hours, affecting a large portion of the state with the potential for mainly large hail and damaging winds. The threat may be enhanced dependent upon the MCS evolution and if the potential derecho does indeed take form. Later updates may alter forecasts slightly to increase the severe weather threat.

Otherwise, enjoy the hot and humid day throughout a majority of the state with temperatures in the upper 80s and 90s and dewpoints in the 70s. Clear skies for a majority of the afternoon will make conditions feel like the 100s in some areas though.