textproduct: Des Moines

KEY MESSAGES

- High confidence in an accumulating, narrow snowband tonight into Tuesday morning, primarily over southwest into parts of south central Iowa. Light snow and rain then drifts north through Tuesday, but any new accumulations are minimal farther north.

- Windy Wednesday with showers and a few storms along a cold front late in the day into Thursday. No apparent widespread severe risk.

- Signal remains for a wet pattern and threat of heavy rainfall, though trends are delaying this until later in the weekend into early the following week.

SHORT TERM /THROUGH TUESDAY NIGHT/

Issued at 330 AM CDT Mon Apr 6 2026

GOES-East upper level water vapor imagery shows a longwave trough over the eastern half of the CONUS while ridging is over the western CONUS. At the surface, a cold front has settled southward through much of the state with low level cold air advection ongoing. This northerly flow is allowing areas of low level stratus clouds to drop southward out of Minnesota into northern Iowa per Nighttime Microphysics RGB. There are additional clouds in the mid-levels, which are streaming from South Dakota and parts of Nebraska into western Iowa. Light radar returns are not reaching the ground per surface observations with cloud bases generally above 9000 feet at this time. Today, breezy winds averaging 10 to around 15 mph will prevail under a partly to mostly cloudy sky with a surface high pressure tracking into the western Great Lakes while the surface cold front settles into Kansas and Missouri. There will be an attempt to produce light rain or snow over parts of the western half of the state as weak low level theta-e advection begins. However, this precipitation will be fighting against low level dry air being funneled in from the high passing to the northeast. With expectations that the dry air will be detrimental to the precipitation, have trimmed and lowered PoPs from initial National Blend of Models (NBM) guidance.

As we head into tonight, the low level theta-e advection will intensify as a strengthening frontogenetical (fgen) band in the 850- 700mb layer sets up a precipitation axis over southwest into south central Iowa into northeastern Missouri. The high to the north will tightening the northern edge of the precipitation shield as the dry air eats away at saturation in the low levels with the current forecast attempting to reflect this gradient. While deterministic models vary greatly on the placement of this band of precipitation, which is often the case, AIGFS and AIFS both have similar placement of the QPF axis. While the AI solutions do not handle the amounts well, they have shown skill in the location of the band. Therefore, have opted for the WPC QPF, which has similar placement to the AI solutions, but has magnitude towards six tenths. Forecast soundings point to near surface temperatures just above freezing, but as wet bulbing occurs early this evening, a transition to all snow is expected across all of southern Iowa. Varying degrees of lift are shown generally above 2km with moderate to strong lift in the traditional dendritic growth zone (DGZ), though the depth is not remarkable. Below 2km, subsidence and northeasterly flow is shown so not sure how much the lesser known DGZ will play a role in snow ratios, which should be mainly below 10:1. Looking at straight model output snowfall is quite concerning with a streak of 6"+ shown in southwest to south central Iowa with CSQ Cobb output tables similar. The challenge will be the snow accumulation on the ground as 4" soil temperatures are in the middle to upper 40s. Snow rates have proven to play a crucial role in overcoming these warm ground temperatures with rates of around 0.75"/hr being sufficient to start accumulation. With the strong forcing, there is potential for higher rates with the latest SREF and HREF showing a 20-30% of 1"/hr rates overnight with mean rates of half to three-quarters of an inch expected. This brings the snow accumulation axis of 2 to 3 inches from around the Omaha metro to Atlantic, Creston, and Lamoni. At this time, not planning a winter weather advisory given amounts generally under 3 inches and the time when much of the snow will fall. However, the wet, slick snow is likely to impact the Tuesday morning commute in southwest and south central Iowa so will be monitoring observational and model trends. While temperatures overnight will be below freezing, not planning any freeze headlines over southern Iowa as conditions were similar just yesterday/Sunday morning.

The snow over southern Iowa will begin to lift northeastward through the day Tuesday as the theta-e advection pushes in a similar direction. As temperatures warm, the initial snow at a given location will mix with and change to rain. With the fgen weakening by Tuesday morning, precipitation will be lighter than tonight and any new snow accumulations after daybreak Tuesday will be near if not under an inch over southern into central Iowa. The precipitation should wane into Tuesday night with a brief dry period.

LONG TERM /WEDNESDAY THROUGH SUNDAY/

Issued at 330 AM CDT Mon Apr 6 2026

A shortwave trough crossing the southern Canadian prairies will have an associated surface low ahead of it with a southwestward trailing cold front, which will reach Iowa late Wednesday. Ahead of this front, breezy winds from the south and southwest will prevail at 20 to 30 mph with gusts of 30 to 40 mph. Fire weather concerns should be minimized as minimum relative humidity values stay above 40%. As the front moves through Wednesday night into Thursday, scattered showers and a few storms are expected along this boundary. Widespread severe weather prospects continue to look low in this period due to weak instability despite otherwise favorable low level kinematics and deep shear. Precipitable water values and warm cloud depths look seasonal so not looking at exceptional rainfall, but amounts up to 1 to 2 inches will be possible with this front.

The front should slip south of Iowa Thursday night or Friday, though how far varies in the models and this impacts the position of a surface high on Friday. These surface features along with the mid-level ridge over the eastern US, which continues to trend slightly westward delaying the off-of-California shortwave trough, are evolving the heavy rainfall threat later into the weekend and early next week. This is reflected in lower NBM PoPs that have trended down on Friday. However, the persistent signal for an active, wet pattern remains as the California trough eventually moves through the Desert Southwest and lifts northeastward towards the state with the GFS and ECMWF both negatively tilting it early next week. Will be monitoring heavy rainfall threat with QPF values ticking up by another 1 to 3 inches from Saturday night through early next week. More details on the impact of this potential rainfall in the hydro discussion below. Finally, a window for severe weather may still develop over the weekend with NSSL GEFS showing 10 to 15% probabilities and Colorado State University's machine learning random forest outlook showing 15 to 30% on Sunday.

AVIATION /12Z TAFS THROUGH 12Z TUESDAY/

Issued at 618 AM CDT Mon Apr 6 2026

A mix of VFR and MVFR ceilings are in place across the state this morning. The stratus across parts of northern Iowa is fairly patchy, but more widespread MVFR stratus is present across southern Minnesota and will move across the northern part of the state this morning before dissipating midday. A few of the northern TAF sites could alternate between MVFR and VFR with breaks in the stratus until ceilings eventually rise after 17z. Some showers are possible in the late afternoon at KDSM/KOTM, but only a prob30 has been introduced for KDSM given southward trends of the precip. A snow band will form towards the end of the period, likely impacting KOTM/KDSM at some time near or after 12z Tuesday.

HYDROLOGY

Issued at 330 AM CDT Mon Apr 6 2026

Many rivers are cresting or will crest over the next 24 hours or so with about 15 forecast points reaching action stage. The Cedar River at Cedar Falls has reached minor flood stage and we are also monitoring the Iowa River near Tama that is expected to crest near flood stage Tuesday morning.

The precipitation today into tonight, including the snow band, will largely fall over areas that have not seen the higher rainfall that occurred last week. NASA SPoRT GFS forced 0-10cm and 0-40cm soil moisture percentiles are forecast to recover to between the 30th and 70th percentiles by late this week. While river forecast are only accounting for 24 hours of precipitation, both the official forecast and the 120 hour contingency forecast show all current action or minor flood stage forecast points falling below action stage by late this week, though they are unlikely to return to their base flows of early last week.

Some rainfall up to 1 to 2 inches will fall with a cold front Wednesday into Thursday, which may take away some soil capacity as the active, wet pattern sets up late this weekend into early next week. A few additional inches may be possible over portions of the state, but uncertainty on amounts and placement within any given basin at this time range remains high. The GFS and NBM forced National Water Model high magnitude flow annual exceedance probabilities are generally 50% on larger streams. This points to renewed river rises that are generally within bank, with this especially shown over southern into eastern Iowa. The experimental Flood Hazard Outlook from late Sunday continues to highlight much of Iowa for limited potential flooding impacts with the experimental Hydrologic Ensemble Forecasting Service (HEFS) at the 30% chance of exceedance with stages similar to current, but at the 10% chance of exceedance with several more points reaching minor stage and a few to moderate stage. Trends in the heavy rainfall signal will need to be monitored this week.

DMX WATCHES/WARNINGS/ADVISORIES

None.