textproduct: Des Moines

KEY MESSAGES

- Showers and thunderstorms return to the area with low (20-30%) rain chances in the west Thursday afternoon/evening, then near 100% chance of rain Thursday night. There is a low chance of severe weather in western Iowa during the day, but a more widespread potential for heavy rain Thursday night into Friday morning.

- Additional rain and thunderstorms are possible on Friday, with a isolated threat for severe weather. Relatively cooler and quiet weather is then forecast Saturday through at least Monday.

- Breezy conditions are expected Friday afternoon with wind gusts reaching up to 40mph.

SHORT TERM /THROUGH FRIDAY/

Issued at 402 AM CDT Thu Jul 30 2026

After a benign Wednesday, big changes will arrive today. We kick off this morning keeping an eye on a mid level shortwave trough positioned over northern South Dakota. Current satellite imagery reveals a cluster of showers and non-severe thunderstorms over northern Nebraska and southern South Dakota, currently thriving on rich low-level moisture and moderate MLCAPE values. However, as these storms continue to push eastward, they are expected to run out of steam upon entering a more stable airmass characterized by mid level dry air. Now one thing worth noting is, if these storms can survive as they enter western IA, due to the dry air in the mid to low levels, could enhance evaporative cooling and yield a gusty wind threat. This will be something to monitor through the morning if instability can persist longer than guidance suggests.

Attention then shifts to a more widespread convective and heavy rain event Thursday night into Friday. Initial shower and thunderstorm development will take place along a cold front over in the Central Plains Thursday afternoon. Convection is expected to quickly consolidate into a linear complex, entering our area late Thursday night into early Friday morning. Damaging winds will be the primary threat with this line of storms as it enters western Iowa, but severity will wane as the system tracks east and encounters less instability over central Iowa. Still, an isolated damaging wind threat could linger in western Iowa before the line diminishes. Outside of the severe risk, abundant deep-layer moisture will also accompany the system, presenting a heavy rainfall and potential flash flooding threat. Further details are available in the HYDROLOGY section below.

A second round of active weather remains possible on Friday, though confidence in specific details is lower. The evolution of the surface low driving Thursday night's rainfall will play a critical role in Friday's severe threat. While the primary line of showers and storms should exit the area Friday morning, secondary convective development remains possible on the backside of the low. Meanwhile, guidance indicates some clearing from Des Moines southward across southern Iowa. This corridor will be closely monitored, as airmass recovery following morning convection could support strong to severe thunderstorm redevelopment. Models suggest a thin stripe of SBCAPE values recovering to 1500-2500 J/kg within this destabilizing warm sector and ahead of the cold front. Additionally, strong surface cyclogenesis will foster enhanced low level helicity; paired with 03 km CAPE around 150 to 200 J/kg and low LCL heights, stretching could yield a conditional threat for a few tornadoes. Ultimately, this risk is highly conditional on daytime clearing. Lingering morning clouds or rain would limit boundary layer destabilization and quickly suppress the severe threat.

Also of note with this system passage on Friday will be the potential for some gusty synoptic winds wrapping around the back side of the passing surface low. This will first be noted over northwest Iowa Friday afternoon, before tracking south and east through the evening. Wind gusts of 30 to 35 mph are expected, with some even stronger gusts over 40 mph possible as downward momentum is enhanced by the drying precipitation field.

LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/

Issued at 156 PM CDT Tue Jul 28 2026

By Friday night the low pressure system discussed in the SHORT TERM discussion above will be departing to the east/southeast, with some showers and perhaps a few thunderstorms lingering into the night before likewise departing. By Saturday the southwestern U.S. deep-layer ridge will have been shunted westward by the trough deepening over the central U.S., being centered somewhere around UT/AZ/NV by Saturday afternoon. This will result in cooler northerly mid-level steering flow over Iowa. Meanwhile, a surface ridge will build down the Upper Midwest in wake of Friday's low pressure system, bringing modest northerly breezes to Iowa by Saturday, then variable winds later in the weekend. While Friday temperatures will thus be generally cool due to rain and cloud cover, this weekend will present a more enjoyable "cool" weather spell with clearing skies, generally light winds, and highs in the low to mid 80s. This will be a far cry from the intense heat experienced across the region last weekend!

Next Monday will be largely the same as the weekend, with highs around the low to mid-80s, mostly sunny skies, and light winds as the surface ridge begins to move away to the east late in the day. Another surface trough/front will then approach from the Dakotas on Monday night and Tuesday, then stall out somewhere across the region around the middle of next week. Just after this, a broad 500 MB trough will round the base of a large gyre over Canada, passing through the Upper Midwest and providing some modest forcing for ascent sometime between Tuesday night and Thursday or so. This is a classic set-up for multiple rounds of showers and thunderstorms along the stalled frontal zone, however, it remains to be seen where that will occur or how the timing and details will shake out. At any rate, after a dry period from Friday night or Saturday through at least Monday, some chances for rain will return around the middle of next week.

AVIATION /12Z TAFS THROUGH 12Z FRIDAY/

Issued at 642 AM CDT Thu Jul 30 2026

VFR conditions to prevail through Thursday evening. A few showers and storms will build in western Iowa this afternoon around 18z but showers are not expected to impact terminals. Confidence is higher that showers and a few storms will impact terminals early Friday morning starting at 03z until the end of this TAF period. Ceiling and visibility restrictions may occur during heavy rain showers and thunderstorms.

HYDROLOGY

Issued at 121 PM CDT Wed Jul 29 2026

Potential for heavy rainfall Thursday night into Friday morning as thunderstorms move across the area. NAM solutions depict very deep warm cloud depths around 5 KM and PWAT of 2.4-2.5" supporting very efficient rainfall processes. However, most other model solutions are a bit less extreme with warm cloud depths of 3-4 KM and PWAT of 2.0-2.1", which still support some heavy rain threat but not quite as alarming. In addition, there is broad consensus that the main swath of showers/storms moving through the area Thursday night will be progressive, limiting overall rainfall amounts and precluding any widespread Flood Watch at this time. That being said, with efficient rates likely, any deviant motion or backbuilding storms could lead to localized heavy rainfall amounts.

Risk of flash flooding (initially) and subsequent river flooding returns to our CWA late in the work week due to aforementioned heavy rain potential. For the flash flood risk, the most likely QPF scenario would mainly confine flash flood concerns to urban areas, where ponding or lower-end flash flooding may occur. Crops in the rural areas are well into their growth which tends to significantly increase infiltration capacity. Three potential gotchas are (1) slightly elevated soil moisture percentiles from central into northeast IA, which would increase the risk of runoff in rural areas; (2) intense rainfall rates may increase the risk of increased runoff in rural areas; (3) rainfall that overachieves vs. QPF would increase the flash flood risk even in rural areas. Rural rain amounts that exceed ~3-4 inches over a few hours would especially increase the risk.

River flood risk depends significantly on rainfall amounts, location and timing. Presently the most likely scenario is moderate to significant within-bank rises on many streams with a few river forecast points possibly reaching action stage, but remaining below flood stage. Rainfall that overachieves vs. QPF would result in higher stages, with possibly up to a few river forecast points reaching minor flooding.

DMX WATCHES/WARNINGS/ADVISORIES

None.