textproduct: Des Moines

KEY MESSAGES

- Band of moderate to heavy snow wanes into the daylight hours today sputtering out to patchy light snow and rain that lifts northward through the day. Any new accumulations after sunrise are minimal.

- Warmer, windy Wednesday. Widely scattered showers and a few non-severe storms possible late in the day into Thursday. Monitoring for possible elevated fire weather conditions too.

- Additional storms possible late Thursday into Friday with a few stronger storms possible.

- While the forecast continues to show several rain episodes this weekend into next week, rainfall total are trending lower and will continue to monitor the heavy rainfall signal.

SHORT TERM /THROUGH WEDNESDAY/

Issued at 317 AM CDT Tue Apr 7 2026

Early morning radar shows a band of high returns upwards of 45 dBZ from the Omaha metro through southwest into southern Iowa early this morning. This precipitation has been forced by strong frontogenesis centered in the 850-700mb layer per latest SPC mesoanalysis. Cross sections show upwards of 8 hours of strong lift in the dendritic growth zone (DGZ) atop this frontogenesis. While much of the evening the precipitation was rain, between midnight and 1am a webcam in Creston and surface observations showed a transition to snow due to finally wet bulbing sufficiently with the temperature falling from 39 to 33 degrees at Creston. Some snow or slushy accumulations are occurring on roadways under the highest radar returns as of this writing with eyeballing an inch or so off of Iowa DOT plow cams and the Creston webcam as pavement temperatures are 32 or 33 degrees. Evening HREF has about 5 hours of 1 inch/hour snow rate probabilities of at least 30%, which would be occurring now and aligns with SPC mesoscale discussion 365. If these rates are achieved and can maintain themselves to overcome the warm surface, then several inches of snow accumulation are possible with perhaps isolated sweet spots up to 5 inches. Forecast soundings over the next few hours also show that there is warming occurring around 850mb, which aligns with the push of theta-e advection northward. It's possible there could be partial melting of snowflakes in this layer to reduce the dendrites formed or to result in graupel/ice pellets, which has occurred in the Omaha metro per their NWSChat room. While the reflectivity band is impressive, it is equally impressive the dry air intruding into the northern side of this precipitation shield causing a sharp cutoff in the precipitation. Dewpoint depressions of 15 to 20F are shown from Denison to Audubon, Des Moines, and Knoxville, and Ottumwa. This has shown up well in the cross sections. Based on all observations available, there is no data pointing to a need to upgrade to a warning; however, will be monitoring for possible cancellation of a few counties on the north side of the current advisory.

The strong forcing wanes fairly quickly after sunrise this morning as the theta-e advection tries to push the precipitation northeastward. However, it will still be fighting the dry northeasterly flow from the surface high pressure over the Great Lakes, which should result in this precipitation being more patchy and light. Precipitation type first thing this morning will be predominately snow, but will begin to mix with rain with the type favoring all liquid by late in the day. Any snow accumulations will be quite minimal at or under a half inch after sunrise. Spotty showers may persist in some portions of central Iowa into tonight as theta-e advection continues.

LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/

Issued at 317 AM CDT Tue Apr 7 2026

While tonight and Tuesday will be more wintry, more spring-like conditions are forecast for Wednesday as strong winds from the south and southwest deliver much warmer conditions as highs reach the 60s to around 70 degrees. Initial sustained winds from the National Blend of Models looks reasonable when compared to forecast soundings from the NAM and GFS at 20 to 30 mph. Wind gusts may need to be bumped up a few knots/mph as top of mixed layer winds are between 40 to near 50 knots. However, this is a warm air advection (WAA) regime so the momentum transport is typically not as efficient. Proof of this is the lift shown in forecast soundings, which will be working against full transport. Wind gusts of up to around 40 to 45 mph will be possible and will have to monitor for possible wind advisory conditions. These breezy winds will drive Grassland Fire Danger Index into the high to very high category and will be monitoring for an elevated fire weather day. Mitigating factors to more critical conditions are green-up underway in southern parts of the state and minimum relative humidity values of 30 to 40%.

These windy conditions will be ahead of a cold front, which will be pushed into the state as low pressure tracks over southern Canada prairies towards Lake Superior on Wednesday. Widely scattered showers and a few storms will develop along this boundary, but there is not a lot of time to recover moisture with perhaps some component of Gulf moisture with dewpoints mainly in the 40s. Instability has and now even deep layer shear looks rather marginal so severe weather continues to look unlikely, which is supported by the day 2 general thunder area from SPC. The front will push to near the Iowa Missouri border by Thursday morning and stall. As a pulse of theta-e advection interacts with this stalled boundary, scattered showers and storms are likely to result late Thursday into Friday morning. Instability will be a bit higher with more deep layer shear along and south of the boundary, though the steeper lapse rates look to be over western Iowa and points southwest. This could result in a few stronger storms with rain totals in spots up to around 1 to 1.5 inches. Surface high pressure and its drier air will nudge the boundary south of the state on Friday, which should offer a 24 to 36 hour period of dry conditions later Friday into a part of Saturday.

As has been discussed over the last several days, a more active, April pattern looks to set up this weekend into next week. Trends over recent nights has been for this to set up later into the period just outlined due to downstream high pressure trending westward, which is holding up the southwesterly flow from arriving. QPF has also been trending lower over the last several nights and will have to see if this continues to hold, though several rain episodes are still expected. The first round will be spurred by a lead shortwave kicking out into the region later Saturday with a California shortwave trough following it on Sunday. These features will promote intervals of showers and storms from later Saturday into Sunday night. There will be a good plume of moisture ahead of these waves with above normal precipitable water values near 1.5 inches and seasonally high warm cloud depths. There could be a window for severe weather on Sunday with NSSL GEFS severe probabilities at 15 to 30%. A change from previous forecasts is that another trough will dig over the western US late this weekend and move into the central US towards Tuesday or Wednesday and bring another round of storms to the region. While details will continue to evolve, will have to continue to monitor for potential heavy rainfall with additional details in the hydro section below.

AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/

Issued at 640 AM CDT Tue Apr 7 2026

VFR conditions are in place across the TAF sites this morning despite ongoing snow in the southwest part of the state. The snow will lift north and east while continuing to dissipate and potentially impact KOTM and KDSM in the morning. Because the band is dissipating, only a prob30 is given to these sites. Additional showers will develop this afternoon and evening across the state, but will be scattered in nature and prob30s are given to reflect the uncertainty. MVFR ceilings will move north across the state through the morning/afternoon before lowering in the early evening and perhaps crossing IFR thresholds for several hours from 0z-2z. Ceilings will likely be near the IFR threshold so this will continue to be monitored for the 18z update. This stratus deck will clear out entirely during the night, likely clearing all sites around 9z. Winds will be gusty during the late night hours, and there is potential for marginal wind shear near the end of the TAF period.

HYDROLOGY

Issued at 250 PM CDT Mon Apr 6 2026

Many streams are cresting now or will crest over the next ~24 hrs with around 15 river forecast points reaching action stage. The Cedar River at Cedar Falls has reached minor flood stage and the Iowa River near Tama that is expected to crest around 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 0-10 cm and 0-40 cm soil moisture percentiles are forecast to recover to between the 30th and 70th percentiles by late this week. While official river forecasts account for only 24 hours of QPF, both the official forecasts and the 120-hr contingency forecasts show all current locations in action or minor flood stage to fall below action stage by late this week. They are unlikely to return to their base flows of early last week though.

Rainfall up to 1-2 in 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. Up to a few additional inches are 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 data suggests renewed generally within- bank rises especially shown over southern into eastern Iowa, with some isolated minor flooding possible. The experimental Flood Hazard Outlook (FHO) continues highlighting much of Iowa for limited potential flood 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 continue to need to be monitored.

DMX WATCHES/WARNINGS/ADVISORIES

Winter Weather Advisory until 1 PM CDT this afternoon for IAZ057-070>072-081>084-092>095.