textproduct: Des Moines

KEY MESSAGES

- Band of moderate to heavy snowfall over southwest Iowa this evening into Tuesday morning. Snow amounts of 2 to 5 inches likely, with a narrow swath of 6+ inches possible.

- Light snow transitioning to light rain possible into mid-day on Tuesday.

- Warmer and windy conditions expected on Wednesday. Scattered showers and thunderstorms possible Wednesday afternoon into the evening.

- Active weather continues at times Thursday through the weekend.

SHORT TERM /THROUGH TUESDAY NIGHT/

Issued at 254 PM CDT Mon Apr 6 2026

Northerly flow behind last nights frontal passage has led to cool and breezy conditions today. Surface high pressure filling in over Iowa has kept things dry at the surface, but increasing frontogenesis/lift aloft has led to weak radar returns and mid-level cloud cover over the southwestern half of Iowa. However, with the 20 degree dewpoint spreads below these returns, and the patchiness of clouds on satellite imagery, it's clear that the dry air is winning out and little is reaching the ground. A few sprinkles remain possible this afternoon and evening as this mid-level moisture continues to precipitate down into the layer, but chances for any appreciable precipitation is low.

Precipitation chances increase considerably this evening, as the theta-e advection from the southwest continues to smash into the cool, dry air mass overhead. This battle between the two advection regimes will lend itself to a slanted region of frontogenesis from roughly 850 mb to 650 mb. Model cross sections and soundings indicate over -20+ microbars of lift roughly collocated with the dendritic growth zone and super saturation with respect to ice within this layer, resulting in a band of moderate to potentially heavy snowfall. This band will also be favorably positioned withing the right entrance region of the upper level jet, further promoting broad-scale lift. HREF output shows 40 to 50% of members with >1" per hour snowfall rates overnight within this band, further emphasizing the potential for heavy snowfall falling within the band. Snow ratios may be a tad on the wetter side, but over 0.5" of modeled QPF will more than make up for the lack of higher snow ratios. However, we can't go without mentioning the intrusion of dry air that will still be ongoing on the northern fringe of this band, as the dry air mass to the north tries to work against the band. While this won't prevent snowfall underneath the zone of strongest forcing, this will cut into the northern edge of the heaviest band. The net result will be a band of snowfall generally around 2 to 5" with locally higher amounts of 6" or more in a narrow swath within the band. Given the dry air intruding from the north, this band will likely have a sharp cutoff of snowfall amounts, especially along the northern fringe. With the higher end potential for heavy snow embedded within the band, have issued a Winter Weather Advisory for areas most likely to be impacted by the band. An upgrade to Winter Storm Warning will likely be needed later this evening to capture the location of the narrow swath of higher amounts once confidence in the exact location increases. Areas that do receive this wetter, heavier snow should expect slick travel during the Tuesday morning commute.

While the heaviest band of snow is expected over southwest Iowa, precipitation will drift northward into the day on Tuesday as the high pressure departs off to the east. However, forcing will diminish as this occurs and saturation will be more difficult to come by farther north into the drier air. Therefore, light snow chances will drift northward through late Tuesday morning into the afternoon, but accumulations will be minimal. A transition over to rain may also occur as low level temperatures warm through the day.

LONG TERM /WEDNESDAY THROUGH SUNDAY/

Issued at 254 PM CDT Mon Apr 6 2026

A 500 mb trough digs into the midwest on Wednesday. A healthy low level jet will develop ahead of this system, advecting warm, moist southerly air up into Iowa. With this jet aloft winds will become quite breezy on Wednesday. Warm air advection regimes aren't the most efficient at transporting winds aloft down to the surface, but thermal mixing on Thursday tapping into a 50 to 60 kt low level jet will still result in windy conditions at the surface, even if the entirety of those winds aren't realized. NBM winds are already suggesting sustained winds around 20 to 30 mph and gusts up to 40 mph, and modeled soundings from the GFS imply winds could be even stronger than this thanks to steep low level lapse rates and 50 kt winds at the top of the mixed layer. Although not a prime high wind environment, would not be surprised to see both sustained winds and gusts approaching wind advisory criteria and will be assessing the need for any wind headlines in the coming days. With the plume of low level gulf moisture that will come up with this system, we will also be looking at the potential for showers and a few thunderstorms ahead of the trailing cold front. That said, instability looks minimal and severe weather threat is low at this time.

As has been discussed in multiple previous discussions, the progression of this front will dictate how wet it will be through the end of the week. Last night's guidance suggested the front may fall through the state and keep most of the area dry through Thursday. However, recent guidance suggests it may stall over Iowa, bisecting the state and keeping rain and thunderstorm potential in place over southern Iowa on Thursday before fully pushing through the area on Friday. This progression would give us a brief lull in rain chances through Friday and into Saturday, before the broad upper level trough develops over the western CONUS into the second half of the weekend. This will open the state up to the gulf once again and put us into a moist, active southwest flow pattern. Rain and thunderstorms are possible throughout this period, but with this being an ever-changing scenario, will hold off on any farther details at this time.

AVIATION /18Z TAFS THROUGH 18Z TUESDAY/

Issued at 1231 PM CDT Mon Apr 6 2026

MVFR clouds over northeastern Iowa are slowly eroding early this afternoon, and will give way to VFR conditions through the next few hours. Winds have been breezy out of the north northwest, with gusts around 20 to 25 kts. The higher gusts should diminish some later this afternoon, but remain light to breezy into the evening. Mid-level clouds and light rain will drift over the state through the afternoon, although impacts are expected to be minimal. Later tonight and into Tuesday morning, a band of snow will develop across southeastern into south central Iowa. Expectation is for this to mostly stay south and west of KDSM and KOTM, but a slight shift could lead to some impacts at either site. Therefore, have included some PROB30s for light snow for both sites. Low ceilings also lift up into the area thorugh Tuesday morning, leading to MVFR to IFR conditions.

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 from 10 PM this evening to 1 PM CDT Tuesday for IAZ057-058-070>072-081>084-092>095.