Severe weather looks to be an issue tonight through Central Iowa as a cold front moves through the Upper Midwest. The primary concerns look to be damaging winds and large hail with these storms.
Dew points will rise this afternoon in the mid-70s with a plume of that moisture feeding into Iowa from Oklahoma, Kansas and Missouri ahead of the approaching cold front. This in combination with heating here at the surface with some partial clearing through mid day will result in quite a bit of rising air or what we call buoyancy.
Storms will first start to fire up along the front in northwest Iowa from Carroll to Fort Dodge around 3 to 4 PM. The line of storms will move southeast arriving in Ames to Des Moines from 5 to 6 PM.
The thunderstorms will continue to develop and linger through Central Iowa from Ames south towards Creston and Osceolat through 8 PM. Places like Ottumwa and Centerville will see the storms around after 9 PM.
These storms will first develop as individual cells but will transform into clusters later into the evening. The primary threats are large hail and damaging winds. A brief tornado cannot be ruled out by the dynamics are not fully supportive of tornadic development.
The cluster of storms look to persist through the evening along and south of I-80 leading to a heavy rain threat. Winds are weak and the precipitable water levels are high. This will mean persistant storms that may sit over the same locations re-building on themselves through the evening and into the night. 1 to 3″ of rain looks common, but some localized areas may see up to 6″.
No Flash Flood Watch has been issued at this time due to exact location inconsistencies and dry conditions with moisture starved crops, needing rain. Rivers are also on the low side so there is capacity to hold a good deal of added water. As the rain comes down, isolated flash flood warnings may be needed in the night if ponding of roads and ditches does begin to be a problem.
Wednesday there will still be some lingering rain across southern and southeast Iowa with a isolated shower or two into the afternoon, but the main forcing will be east of Iowa. High pressure begins to build in from the west with clearing skies Wednesday night and dry conditions on Thursday. Attention will then turn to extreme heat for the weekend.