Area Forecast Discussion

KEY MESSAGES

- Very low potential for showers and thunderstorms in far southeast Iowa this evening (<10%).

- Elevated fire weather conditions expected over north/northwest Iowa Wednesday.

- Slight Risk (level 2 of 5) for severe weather over the western half of Iowa for Thursday. A Marginal Risk (level 1 of 5) covers the eastern half.

SHORT TERM /THROUGH WEDNESDAY/

Issued at 248 PM CDT Tue Apr 21 2026

Warm and dry conditions are common across the forecast area early this afternoon, with mostly sunny skies and temperatures ranging in the upper 70s to low 80s. Temperatures should increase another degree or two this afternoon, especially over southwestern Iowa. A bit tough to tell, but the advertised weak surface boundary is generally located just south of I-80, noted by the breezy winds out of the southwest and dewpoint values in the 50s, while further north of the boundary, winds are generally light and variable, while also drier with dewpoints in the 30s through the mid 40s. As this boundary very slowly sinks south towards this evening, could see some development of weak showers and storms (noted where cumulus has formed over very far southeastern Iowa), though overall guidance continues to trend downward on the extent of this activity. This is likely due largely to the overall presence of low level dry air, and also weaker forcing into this area. Therefore have decided to remove mentions for showers/storms southeast, with overall chances now around 10% or below. Will be monitoring trends through the next several hours though given the off chance moisture return is greater than expected.

Tonight into Wednesday morning, the mid-level ridge currently over the western CONUS will continue its easterly track, eventually moving directly overhead Iowa later in the day. Increasing moisture return and WAA will allow for overnight temperatures to be on the mild side, with lows in the upper 40s to mid 50s north and in the upper 50s south. Strong southwest flow at 850mb with temperatures around 16-18 C will move over the western third to two-thirds of Iowa later this morning into the afternoon, allowing for another warm and breezy day. Highs in the upper 70s to low 80s are expected, along with breezy surface winds gusting to 20-25 mph under mostly sunny skies. The warm and breezy conditions, paired with minimum RH values in the low to mid 30s over north/northwest Iowa and dry fuels will lead to elevated fire weather conditions. Burning in these areas should be avoided if possible.

LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/

Issued at 248 PM CDT Tue Apr 21 2026

The pattern is still expected to shift more on the active side come Thursday, as a large mid-level trough and associated surface low circulating over North Dakota slowly drags a cold front through the Midwest. To start the day, this boundary is expected to be located somewhere over far western Iowa, where models such as the NAM and GFS are showing developing showers and thunderstorms ahead of this feature. Into the late evening though, a potent shortwave on the southern fringe of the larger mid-level feature tries to develop a surface low over southern Minnesota per NAM/Euro, which paired with an increasing low level jet into Iowa enhances the forcing into Central Iowa and therefore the development of more widespread shower/storm development, while the GFS lacks this particular feature. Considering the slight differences in the timing of the cold front passage over Iowa, due to a lag in progression of this features, as well the evolution of features passing through, will need to keep an eye on trends closely. There remains the potential for severe weather, particularly by the evening and overnight with instability values around 1500 J/kg and plenty of shear around 35-40 knots. Steep lapse rates up to 7.5 C/km as well would suggest a threat for large hail. The Slight Risk remains largely over western Iowa, and a Marginal further east per SPC.

Lingering showers and storms are looking to occur mainly in the eastern half of the state through sunrise as the front slowly departs. Drying conditions are expected through the rest of the day Friday, while the mid-level low pressure system generally remains over the Northern Plains. This will lead to a more unsettled pattern for the weekend as a few weaker waves pass through the region, while temperatures will generally range just a tad cooler than previous days with highs expected in the 60s.

AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/

Issued at 1239 PM CDT Tue Apr 21 2026

VFR conditions are expected to remain across the terminals through the period. Besides some high clouds, mostly clear skies are expected. A weak surface boundary will continue to slowly descend over central Iowa, leading to variable winds across the state, and most breezy over the southern half of Iowa where gusts up to 15-20 knots will continue to decrease over the next few hours. There is a low signal for patchy fog around sunrise Wednesday near/at KALO, KDSM, and KOTM, though have left out of the terminals for this issuance given low confidence but will continue to monitor.

DMX WATCHES / WARNINGS / ADVISORIES

None.