Severe Weather: June 26

4:30 PM Update: Warm frontal boundary looks to be situated from northern South Dakota near Aberdeen, SD extending southeastward through Pipestone, MN to Mason City, IA. To the east of that point, the front is barely recognizable given a heavy cloud shield in place over much of Iowa. As of 4 PM, only northwestern and/or extreme northern Iowa is under some type of clearing. Moisture return was limited by the convection this morning, thus only mid 60s are present. This is leading to the lack of instability over the state of Iowa, and eastern Nebraska/South Dakota for that matter. Only moderate instability currently present, but given more hours of sun we should see strong instability in place by 7 PM.

Current forecasts are still struggling with the morning convection, and placement of the warm front currently. The off-hour NAM has the best placement and parameters that are currently in place. Given current SPC thoughts as well with a discussion in place for western South Dakota; it seems likely that storms will develop in western SD/NE and track east/southeastward along and south of the warm front. These storms will track into eastern SD/NE by early nighttime hours with a continued threat of damaging winds and hail. The storms may enter into portions of MN/IA after midnight, with the potential for severe weather continuing. Other development may be able to form along and/or south of the front in eastern SD/NE and potentially extreme western MN/IA. However, this will take substantial increases in instability, and subsequent lift and other parameters; thus is very questionable at this time.

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9:30 AM Update: Yesterday's severe weather threat panned out during the evening and into the overnight hours, with a multicellular line of storms that went through central Iowa. These storms were able to produce large hail and damaging winds over the state, along with fairly heavy rains.

Today we definitely did not have to wait as long for severe weather to come through the state, with a line of storms developing along the SD/NE borders and moving into northwest Iowa. Once again, storms developed in central Iowa as well, some being severe with marginal hail and damaging winds. The storms across central Iowa this morning did produce some hail in Ida county, but have since congealed into a substantial line of damaging winds. From Fort Dodge to Carroll between 8 and 9 AM this morning had several reports of tree and power pole damage, one measured gust was 76 mph in Coon Rapids, IA. This line continues to move east/southeast and is bearing down on the Des Moines metro currently with the continued threat of damaging winds.

Behind this line of storms, other thunderstorms have developed once again over portion of northwest Iowa and into southeast South Dakota. Other development in southeastern Nebraska in more isolated nature has occurred, a few of these cells are even severe warned currently.

The forecast is very complex for the day, but the current belief will be that this is only round 1 of severe weather for the day. Expect clearing to take place behind the several complexes of storms during the early afternoon hours. With return flow being strengthened, and clear skies allowing for warming temperatures, substantial instability should be back in place by late afternoon. With a stationary boundary draped over parts of the plains states, as well as several outflow boundaries from the morning convection, several may serve as development points for more thunderstorms by the evening hours. Developing storms this evening are likely to be supercellular in nature, capable of very large hail, damaging winds, and an isolated tornado is possible near any boundary. The best threat of a tornado with the boundary currently looks to occur through South Dakota and into northwestern Iowa, although other subtle boundaries may still produce tornadic storms outside of this area. Growth of the storms in the early nighttime hours is likely to congeal them into a line over central SD/NE, potentially southern ND. The line will be favored to continue to move east/southeast with time with the potential for a significant damaging wind event to take place over South Dakota, northern Nebraska, extreme southwest Minnesota, and into western Iowa. For this reason, the SPC has upgraded a large portion of the state into a moderate risk category for the combined potential of a significant wind event, and the very large hail potential with isolated development this afternoon/evening.

More updates are possible this afternoon with the evolution of the morning storms, and forecast adjustments. I will be around the northwest Iowa area today, ready for any development this afternoon as the potential is there for a significant severe weather day.