textproduct: Des Moines

KEY MESSAGES

- Showers and storms are slowly clearing northern and northeastern portions of the area as the next round moves in from the west.

- More showers and thunderstorms are expected later today, with locally heavy rainfall possible and a low chance for severe weather.

- Active weather continues Sunday into early next week. Potential for reprieve through mid-week.

SHORT TERM /THROUGH SUNDAY/

Issued at 353 AM CDT Sat Sep 19 2026

Showers and thunderstorms are ongoing across parts of northern/northeastern Iowa. Another area of lighter showers and thunderstorms is encroaching from the west. Also across the north, fog has developed and is struggling to fill in farther south due to cloud cover from the storms out west. The storms in the northeast should continue to be pushed out by the Low Level Jet (LLJ) which is draped across the state with the potential for some straggling showers and storms. Of note, with the ongoing activity in the northeast around Waterloo, HREF probabilities for the same time window hint at the potential for 3+ inches of rainfall in spots. The 00z and 06z suite of deterministic models are much more widespread with QPF values through 18z/1pm at generally less than 1.5 inches.

Other notable features are at play across the state, as a surface low is hiding in central Iowa per surface observations, with a warm front draped near I-80 with a cool front sitting farther back to the west. The resultant warm sector will become the focus through the morning with an area of Theta-E advection would fuel additional thunderstorm development as storms continue to push in from the west. Through the morning, these thunderstorms aren't expected to be too jiggy with limited instability available (500J/kg or less). The surface low will depart the area and lift to the east/northeast, carving the path for another low which is south of Grand Island, Nebraska. More details on this are below.

Locally heavy rainfall is possible with these storms given the same conditions of warm cloud depths around 13kft, PWAT values hovering near 2 inches, and the continued modest moisture transport. That said, this activity is expected to be progressive enough that concerns from widespread heavy rainfall are minimal. The 12-hour HREF probabilities through 18z/1pm Saturday show 1" is the reasonable worst case with this activity.

Moving through the rest of the day, the other focus is on the potential for severe weather. The track of the surface low in south central Nebraska is creating some uncertainty in the northern extent of the severe window. While southern Iowa was already on the periphery of the setup, 00z and 06z guidance now shows that the low will track south of the Missouri border. Another notable shift is with the LLJ. After it fizzles out Saturday afternoon, it should reinvigorate into the evening hours with it now pointed farther south and curving away from the state. None of this is to say that Iowa is 'home free' from severe weather or heavy rainfall, however. The coverage area would just be much more limited than previous guidance had suggested.

In terms of heavy rain, the LLJ would be set up parallel to the boundary which would be supportive of training storms and warm cloud depths of 12kft or higher are still present. High PWAT values meeting or exceeding 2 inches are again present aided by the high pressure system which has now moved into North Texas - this high will play a larger role later. HREF 12 hour probabilities through 15z/10am Sunday shows portions of southern and eastern Iowa could see an inch or more of rainfall, although the probabilities for 3+ inches are low (~10%). Deterministic guidance is generally around 1" as well, with come models showing at or just above 2" through the same time window.

The severe weather threat, on the other hand, looks much more conditional. Like the heavy rain threat, it depends on where the boundary sets up. 1500-2000 J/kg of MLCAPE is present with around 25kts of 0-6km shear. Gusty winds aren't out of the question, and if an updraft can get tall enough marginally severe hail is possible, however with a high freezing level (around 12kft), hail formation will be difficult. Unlike the previous few days, the low level wind field is fairly uniform in direction.

Showers and storms are expected to last into the overnight hours or into very early Sunday morning, but by sunrise should largely be clear of the forecast area. That said, it won't be completely dry. Saturated sounding profiles in the low levels show conditions are favorable for drizzle.

LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/

Issued at 305 PM CDT Fri Sep 18 2026

Our active pattern continues Sunday with additional rain/thunderstorm development possible in the afternoon and evening, as another trough digs in on the lee side of the Rockies. This overall pattern persists into early next week, with rain and thunderstorms possible each day. That said, the 12z global model guidance that's come in today does show some reprieve may be on the horizon toward the middle of next week.

AVIATION /12Z TAFS THROUGH 12Z SUNDAY/

Issued at 613 AM CDT Sat Sep 19 2026

Showers and thunderstorms are ongoing in portions of the state. In the near-term, imapcts are expected at all terminals except KOTM. A warm and moist airmass is in place across northern Iowa, bringing IFR to MVFR ceilings to KMCW, KALO, and KFOD through the entire TAF period. KDSM and KOTM will start as VFR for at least half of the period before lower ceilings move in with the next round of showers and thunderstorms. KOTM is expected to have the longest-lasting impacts from later showers and storms, while PROB30 mentions for thunder were brought to KDSM pending higher confidence in timing with future issuances. Winds will remain light (under 10kts) through the period and will take on a northerly direction around 00z/7pm, though sporadic gusts under thunderstorms are possible.

HYDROLOGY

Issued at 306 PM CDT Fri Sep 18 2026

Heavy rain and training storm potential over northern Iowa tonight may pose a risk for flash flooding, especially in urban areas. The main axis of heaviest rainfall has wavered quite a bit just in today's guidance, but the general consensus is putting our forecast area on the southwestern fringe of the highest QPF. Should the nose of the LLJ and coincident storms set up to our north, our area may be spared from the worst of it. However, there are solutions that show the heavier QPF band a bit farther south into north central Iowa. It's also not uncommon for these areas to leak slightly farther south. Therefore, while the greatest risk does set up to our north and east, have decided to put out a targeted Flash Flood Watch across northwestern Iowa that includes Mason City and Waterloo.

In addition to the flash flood risk, similar areas received 1 to 2" of rain this morning, and could see another 1 to 3" tonight, depending on the main axis. Therefore, river responses will be possible, primarily along the Cedar and Iowa Rivers. The HEFS output suggests gages along these rivers could reach into action or minor flood stage, with higher end scenarios pushing into higher stages.

DMX WATCHES/WARNINGS/ADVISORIES

Flood Watch until 1 PM CDT this afternoon for IAZ007-017-027- 028-039.