textproduct: Des Moines

KEY MESSAGES

- Warming into Monday with near records possible. Elevated fire weather possible southern into western Iowa Monday.

- Strong to a few severe storms possible Monday evening with main threat large hail.

- Turning cooler Tuesday with gusty winds behind a front. Several precipitation chances remainder of the week.

SHORT TERM /THROUGH MONDAY NIGHT/

Issued at 249 PM CDT Sun Mar 29 2026

The next 24 to 30 hours or so will be the more tranquil period of the weather forecast as the pattern turns more active thereafter. This afternoon, breezy winds from the south-southwest have prevailed as lower pressure over the central Rockies develops with these winds also helping to usher in more moisture in the boundary layer. This has helped to keep relative humidity values generally above 30% and critical fire weather conditions at bay with the Grassland Fire Danger Index (GFDI) mainly in the high category. It is also warmer this afternoon with highs well into the 60s to low 70s due to top of the boundary layer temperatures +6C since this time yesterday. As we head into tonight, winds will diminish and be under 10 mph. A few models try to depict light fog development over parts of north central into northeastern Iowa. GLAMP probabilities of visibilities below 5 miles have been dropping in runs through the day so have only included a very limited area of fog east of Mason City to north of Waterloo.

A boundary will reside north of the state on Monday as low pressure moves slowly towards the state. There will be good southwesterly flow ahead of this low, which will pump more moisture and bump low level temperatures up again. High temperatures will reach near record levels (see Climate section below) as they soar into the 80s and in many cases well into the 80s. With better boundary layer mixing, have also lowered dewpoints by a few degrees to account for entrainment from aloft. The lowest relative humidity values will be over western Iowa in the 20 to 30% range; however, the relatively stronger winds will be over southern Iowa. With these fire weather variables spatially out of phase, this will result in elevated fire weather concerns, which will be highest over western into southern Iowa where the GFDI will be in the very high category.

Monday night will see the low level jet ramp up to 40 to 50 knots and this will provide for strong theta-e advection south of and into the boundary. This phased low level thermodynamic and kinematic forcing will be sufficient to develop strong to a few severe storms towards 3z/10pm Monday evening per many high resolution models. These same models try to fester showers or perhaps a storm before that time, but capping should keep things mostly contained until mid- evening. Forecast soundings continue to point to these storms being elevated in nature with MUCAPE in excess of 1500 J/kg, effective shear around 30 knots up to perhaps 40 knots, and steep mid-level lapse rates of 8C/km. These variables point to a large hail threat. While hodographs are elongated (and thus supportive of the hail risk), they are a bit gunky in the CAPE bearing layer above 3km so will be interesting to see how storms evolve tomorrow evening. Forecast soundings also show a good amount of sub-cloud dry air from 3km to the surface such that this balloons downdraft CAPE values with a gradient in values up to around 1000 J/kg towards Iowa Falls/Mason City to around 700 J/kg toward Des Moines. These lower values towards the I-80 corridor are a result of the low level moisture advection. So, the wind threat looks to be isolated/localized to where storms develop and low level moisture advection has not reached to saturate and minimize the effects of entrainment to the surface. Convective allowing models are showing little in the way of gusty winds at this time, but the isolated potential remains given the setup. Much of this storm activity will clear our forecast area into eastern Iowa around or shortly after midnight.

LONG TERM /TUESDAY THROUGH SUNDAY/

Issued at 249 PM CDT Sun Mar 29 2026

Tuesday will be a transition day as the boundary north of the state is forced through the state as an upper level shortwave trough pushes its influence over the northern states. The now cold front will also be the focus for possible storm development in the afternoon into early evening hours - roughly along and east of Highway 63 - though the overall risk will be higher to the east/southeast. In the front's wake, gustier winds will develop from the northwest and usher in cooler, more seasonal air with highs 25 degrees lower in northwestern Iowa (compared to Monday) to a few to 5 degrees lower in southeast Iowa. There should be some degree of a short window of dry conditions after the front clears the area Tuesday night, but another trough will be approaching from the west on Wednesday. Moisture tries to advect ahead of it, but the front will limit the degree of moisture return into Iowa. However, there will be strong theta-e advection that should allow for precipitation to develop later Wednesday into Thursday. Forecast sounding profiles continue to look interesting as they have over the last day with profiles just below freezing and isothermal for some sort of narrow, wet snow area potential on the northern edge of the precipitation shield. As this system slips away on Thursday, a more robust trough will be entering from the Pacific Northwest towards Iowa. Once again, moisture transport will precede its arrival later Friday into Saturday. From a pattern recognition perspective, this setup looks good for severe weather potential later Friday. AI/ML solutions yesterday were rather muted or shunted away from Iowa, perhaps due to meager dewpoints peaking in the low 50s, but today's NSSL GEFS ML severe probability does have an area from Texas into Iowa ahead of the trough along with low probabilities from some other ML severe probability models. As this moves through on Saturday, moisture may try to wrap around into the colder air Saturday night for some additional wet snowflakes in northern Iowa, but that will depend on the placement of the dry slot punch and track of the system. Regardless of severe and snowflake potential, looks to be a good amount of moisture. Global deterministic, ensemble, and AI solutions show parts of Iowa receiving at least 1 to 1.5 inches of rainfall for the 48 hour period ending late Saturday evening. While much remains to be seen with where, how, and how much rain falls, will be monitoring trends in the experimental HEFS (Hydrologic Ensemble Forecasting Service) and the NBM and GFS forced National Water Model with these showing mostly within bank stream responses at this time.

AVIATION /00Z TAFS THROUGH 00Z TUESDAY/

Issued at 640 PM CDT Sun Mar 29 2026

VFR conditions will prevail through the period. Winds gusts will decrease within the next two hours. Southerly to southwest winds will increase to over 10kts after 18z with 20kt gusts possible for KDSM and KOTM. <30% chance of thunderstorms across central Iowa after 22z, mainly around 00z. Highest confidence at KDSM for this TAF period, but not confident enough to include in the TAF at this time.

CLIMATE

Issued at 249 PM CDT Sun Mar 29 2026

Forecast and Record High Temperatures for Select Central Iowa Cities...

============================================= | Monday | Period | Forecast Record/ | of City | High Year | Record ============================================= Des Moines 85 83/1968 1878- Mason City 79 78/1967 1903- Ottumwa 84 83/1967 1923- Waterloo 81 84/1967 1895- =============================================

DMX WATCHES/WARNINGS/ADVISORIES

None.