Severe Weather Outlook for Wednesday, July 26, 2017 - elevated risk in southeast half of state

Heavy Rain with Damaging Wind Threat Wednesday

In All Posts, Forecasts, Severe Weather by Henry LukerLeave a Comment

After a couple days of relatively quiet weather, mother nature looks to ramp back up her game. A look at the surface analysis early this morning shows a low pressure system sitting over the central Great Plains with an associated cold front extending into southeastern South Dakota and stationary warm front hanging southeastward from that point into the mid-Mississippi Valley. Radar shows an ongoing mesoscale convective system primarily over Nebraska with an embedded line producing some damaging winds north of Grand Island. The aforementioned frontal boundaries and activity will shift eastward through today and setup the stage for the next round.

The activity in central Nebraska will continue through the morning, aided somewhat by a atmospheric low-level jet. How exactly this system works out with timing will place a wild card over today’s threat. If cloud sheets within and around this activity prolongs itself over the state and affects diurnal heating, it will greatly affect how much we destabilize. Current thought is that there will be enough heating and subsequent instability to allow for re-development/re-strengthening, with modest shear leading to a déjà vu – a mesoscale convective system with some damaging wind-producing bowing segments. Large hail will also be possible with some of the stronger storms. The Storm Prediction Center has an elevated risk of severe weather over the southeastern half of the state for this reason. The exact placement of all of this depends on where boundaries remain after this morning’s round, and those details will have to be worked out later this morning.

Heavy Rainfall/Flooding

Another big piece of this puzzle is the heavy rain expected over parts of the state that could definitely use it. Western Iowa should receive a nice soaker this morning from the MCS moving in from Nebraska. Though in areas like southeast Iowa, your relief will be experienced with the next round tonight. The new development mentioned above should develop into a fairly robust mesoscale convective system aided once again by the low-level jet. A plethora of moisture available will lead to rainfall rates of 1-2″ an hour with locally higher rates.

The WPC has over 2.5″ of rain marked for Centerville, Bloomfield, Keosauqua, Ottumwa, Fairfield, and surrounding areas. The north is generally expected to get a half inch to an inch and a half with the south more along the lines of an inch to two and a half inches. Locally higher amounts of up to four inches are possible in some of these locations.

Of course, the concern with this is that some flooding is possible along area rivers – the Wapsipinicon and Mississippi Rivers have already experienced high waters from storms earlier this week. Flood Warnings remain in effect for the Wapsipinicon River at Anamosa, De Witt, and Independence and the Mississippi River at Illinois City, Muscatine, New Boston, Keithsburg, Gladstone, Burlington, and Rock Island. For the latest information on river flooding, please visit our River Monitor page. Flooding is also a concern across northeast Iowa, namely Bremer county – while significant accumulation should remain far south of here, any measurable rainfall may put pressure on already very saturated grounds.

Bottom line: showers and thunderstorms will roll through the state this morning with severe weather not anticipated. Storms will re-develop or re-strengthen early this afternoon and primarily cause a heavy rain and lightning issue, however, damaging winds is possible with the bowing segments and large hail with the stronger cells. Flooding will be possible in areas with continual heavy rain.

Stay tuned to the Iowa Weather Network for the latest information throughout the day.

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