textproduct: Des Moines

KEY MESSAGES

- Patchy fog and a few light showers this morning, with dense fog possible mainly far south and southeast.

- Thunderstorms will cross Iowa from west southwest to east northeast late tonight into Friday morning. A few strong to severe storms will be possible, with large hail the primary threat.

- Strong to severe thunderstorms are possible from late Friday afternoon into early Friday night. Uncertainty remains in the evolution of the incoming system, which will impact the potential severity and types of hazards. Watch closely for forecast updates today and Friday!

SHORT TERM /THROUGH FRIDAY NIGHT/

Issued at 158 PM CST Wed Mar 4 2026

Skies remain overcast in Iowa early this morning with a weak surface high pressure ridge draped across the region. A few showers have moved into southern Iowa and patchy fog is being observed around the area. The fog is generally not dense, except in far southern and southeastern Iowa where advisories remain in effect through around sunrise. As the surface ridge gradually moves away today winds will come around to southeast and any lingering sprinkles or showers will exit later this morning, yielding to a mild day as temperatures climb into the 50s to lower 60s. It remains to be seen how much clearing will occur, but with modest low-level mixing this afternoon and the waning influence of the departing ridge, we should see at least some breaks in the clouds.

A deep 500 MB trough will slowly cross the Rockies today into tonight, and by Friday morning it will extend from the Four Corners region up into the northern high Plains. During the day Friday a large vorticity element will eject northeastward out of the parent trough, reaching western Kansas and Nebraska by Friday evening. At the surface, a low pressure trough will form along the Lee of the Rockies today in response to the approaching 500 MB system, and by Friday this trough will shift eastward and extend from somewhere around southwestern Kansas up into eastern Nebraska and western Iowa by late in the day. This is a classic synoptic setup for convective potential across our region. Initially, on Thursday night, as the aforementioned surface trough begins to ooze eastward, a nocturnal low-level jet will spread into Iowa. 850 MB winds of 50-60 KT will promote increasing moisture and isentropic lift, triggering thunderstorms that will spread over much of our forecast area mainly after midnight into Friday morning. Forecast soundings indicate strong shear profiles but also an EML that will prohibit any surface-based convection overnight and limit the magnitude of shear updrafts will be able to tap into. Even so, all indications are that 700-500 MB lapse rates will initially be quite steep, and even modest shear magnitudes are enough to justify a risk of large hail. This will be maximized during the first couple hours of storms reaching a given area, as thereafter the mid-level lapse rates will diminish as the column saturates.

The convective and severe weather forecast for Friday is more complex. As the 500 MB vorticity maximum and concordant surface trough approach, deep-layer shear will increase through the day and by Friday evening 0-6 KM bulk shear values will range from around 40-50 KT in our southeast to near 60 KT in our northwest. Forecast soundings indicate large curved hodographs and while there is a relative lack of low-level backing to maximize near- surface shear, any right-moving storms would quickly realize large helicity values. The biggest fly in the ointment here will be the degree of destabilization that can occur during the day. While there will be a lull in convection after the departing storms Friday morning, high-res models vary considerably on the amount of lingering shower development that will occur during the day, as well as how persistent the associated stratus deck will be. If we remain overcast then instability will be somewhat limited and the threat of surface-based convection lower, but even low CAPE values in the presence of strong deep-layer shear and robust dynamic lift would support a threat of strong updrafts and at least some hail. However, if any clearing can occur at all, then instability in such areas would increase rapidly Friday afternoon/evening, enhancing the threat of hail and strong winds. In addition, if any such storms are able to root to the surface, and particularly if deviant motions or small-scale backing of the winds allow for significantly enhanced vorticity ingestion, then a tornado threat could be realized. The SPC outlooks remain unchanged this morning and cover this possibility well. We will be updating the forecast for severe weather potential continuously over the next couple days in anticipation of this event.

LONG TERM /SATURDAY THROUGH WEDNESDAY/

Issued at 254 PM CST Wed Mar 4 2026

The system quickly departs with high pressure settling across the area through the weekend. Temperatures will be mild on Saturday, then warming further on SUnday with increasing southerly flow into the area. Warm air advection continues into early next week with 60s to near 70 by Monday. The next week looks to remain active with several waves moving across the central US. The next chance for precipitation impacts across Iowa looks to arrive on Tuesday.

AVIATION /18Z TAFS THROUGH 18Z FRIDAY/

Issued at 1144 AM CST Thu Mar 5 2026

Lingering patchy fog will continue to slowly lift over the next hour or so before improving at all sites, though low stratus is expected to remain through the rest of the day, leading to continued MVFR ceilings across the terminals. Clouds are expected to lower further after 06z from southwest to northeast as scattered showers and thunderstorms spread across the state into Friday morning. Uncertainty remains on the exact timing and coverage of storms over any particular terminal, so have continued use of PROB30 groups at this issuance and will continue to refine over the later forecast packages. Low visibilities as well as low ceilings are expected to result in widespread IFR and even periods of LIFR conditions Friday.

DMX WATCHES/WARNINGS/ADVISORIES

None.