Flash Flood Threat Targets Plains, Ozarks, Mississippi Valley, Ohio Valley Into Next Week

Flash flooding will return to center stage in parts of the nation's mid-section in two rounds: wrapping up this week and also kicking off next week.
Yes, former Hurricane Simon will have a role to play, but not the lead role in most areas.
Some areas will get soaked with heavy rain from both phases. Therefore, these areas are where the flash flood threat is greatest.

Round One: Into This Weekend

First up, moisture from former Hurricane Simon, as well as lift from its leftover mid-level circulation, will spread clusters of slow-moving thunderstorms into parts of Arizona, New Mexico and Colorado through Friday.
If this sounds like a familiar story, you're right. The same areas recently dealt with flooding from the remnants of Hurricane Odile and Hurricane Norbert. In addition, there have been a number of other flash flood events this summer in the Desert Southwest.
(FLOOD RECAPS: Phoenix/Moapa, Nevada Early Sept. | Odile's Remnants Spawn Flooding)
Meanwhile, a frontal boundary will stall in a roughly east-west fashion from the central Plains to the Ohio Valley. Moisture from the Gulf of Mexico flowing into the boundary, along with lift from the jet stream flowing parallel to the quasi-stationary front, will help ignite clusters of thunderstorms with heavy rain near the front Thursday through late Saturday.
The map above at right depicts the area of concern for heavy rain over the next 48 hours. Keep in mind locally heavier amounts may fall where thunderstorms repeatedly track over the same areas.
Soil moisture remains high across the northern half of Missouri into central Illinois, so the threat of flooding from this first round appears greatest there. Rainfall rates less than 2 inches per hour would trigger flash flooding there, according to National Weather Service flash flood guidance.
While the soil is not as wet as areas farther north, repeated bands of rain and thunderstorm clusters may also trigger flash flooding in the flood-prone Ozarks.

Round Two: Next Week

If that wasn't enough rain, another soaking is on the way for some of same areas early next week.
A deep southward dip in the jet stream, or trough, will dive into the Plains later Sunday, then swing east though mid-week.
Tapping deep moisture ahead of its attendant cold front, bands of thunderstorms with locally heavy rainfall will lead the front's advance from the southern Plains, Ozarks and Mississippi Valley late Sunday and Monday to the East Coast by Wednesday.
Given the first round's rainfall location, the threat of additional, worsening flooding may rise by Sunday night into Monday in parts of Kansas, Oklahoma, Missouri and Arkansas, then Monday night into Tuesday for parts of the Ohio Valley to the Mid-South regions.
There remains uncertainty regarding how quickly the frontal system sweeps east next week. If it moves slowly, then heavy rain may persist in parts of the Appalachians, Ohio Valley, and East into Wednesday or Thursday.
The map below shows a five-day rainfall forecast from one of our computer models, indicating which areas could see the most rain from both rounds.