textproduct: Des Moines

KEY MESSAGES

- Strong to severe storms are forecast from this evening through the overnight. All severe hazards are possible before the convective complex exits Tuesday morning.

- Relief from the heat starts Tuesday and lasts through the work week before another warmup this weekend.

UPDATE

Issued at 744 PM CDT Mon Jul 20 2026

The Heat Advisory has been expired but also did some tweaks to the grids by incorporating the latest surface observations and radar trends.

SHORT TERM /THROUGH WEDNESDAY/

Issued at 226 PM CDT Mon Jul 20 2026

A classic July NW flow severe weather setup is in store for todays enhanced risk across Iowa. A stacked 500mb trough and surface low is currently approaching Lake Superior and the trailing cold front through Minnesota to South Dakota will be our main storm initiation mechanism today.

To the dismay of most of the recent CAMs, a few storms are already forming along the cold front in southern Minnesota, though these are elevated and the main show is likely to hold off until the boundary layer continues to destabilize. Speaking of destabilizing, the heat today is well underway as the grand finale of the past week of heat. Between the expected highs in the mid 90s and dewpoints in the mid 70s, heat indices across a large part of the state are expected to be between 100-110F. Many stations across central Iowa already have an index over 100F, but mixing out of moisture may keep them from surging too much higher. This will lead to a large zone of 3500+ J/kg of CAPE across north central Iowa as the cold front crosses the state. Hodographs are generally supportive of supercells, particularly further east near the warm front, with decent mid level shear and low level turning. Around mid to late afternoon, early convection along the cold front will have the best chance at briefly supercell mode, capable of large hail and gusty winds. 3CAPE, 0-1 SRH, and vorticity will all be most favorable for a tornado or two near the warm front (likely in or near ARX's CWA), though a powerful updraft sitting on the cold front could be capable of producing a tornado. The relatively large T/Td spreads and strong DCAPE could transition the threat quickly to a more linear mode, and damaging wind would then be the main threat. There is still large uncertainty in storm coverage across the cold front this afternoon. There is a scenario where initiation holds off until mid evening, and another where elevated convection in MN continues to intensify and establishes itself early as it crosses into Iowa.

Storms into this evening and overnight will be dependent on how cold pools are established this afternoon. Convection will likely continue to develop this evening as the increasing LLJ overruns any remnant cold pools and the cold front meanders over central Iowa. A mainly damaging wind threat and perhaps large hail threat will be associated with these storms through the evening and overnight. Additionally, PWATs near 2" and some potential for training thunderstorms would make for a higher flash flooding threat, though this threat will be muted by the low soil moisture and mature crops.

Any remaining storms will likely clear out of southern Iowa by early morning and give way to dry conditions on Tuesday. Relief from the heat will finally arrive Tuesday with highs in the low to mid 80s. Winds will stay quite breezy behind the cold front with gusts up to 30-35 mph in the afternoon. Additionally, the HRRR smoke guidance is forecasting smoke to linger through the day tomorrow, even at the surface, though it likely will be a bit improved from this morning.

LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/

Issued at 226 PM CDT Mon Jul 20 2026

More mild conditions are expected through the end of the work week with highs in the upper 70s and 80s across the state. Continued ridging out to our south and west will continue, but there is decent signal for more shortwaves Wednesday into Thursday that could bring in additional chances for showers and storms. Severe weather is less likely with these storm chances, as moisture will be limited, but more details will be sorted out in the coming days. The ridge is again expected to intensify over the central plains during the weekend and heat will likely return by Saturday and Sunday. Continued NW flow could bring in a marginal chances for smoke haze since wildfires are still ongoing in Canada.

AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/

Issued at 626 PM CDT Mon Jul 20 2026

VFR TAFs are present with this issuance for the 5 TAF sites; however, over the next few hours, a strong convective complex will continue to dive south impacting KDSM and KOTM before exiting the area by 09Z. Terminals KFOD, KMCW and KALO will remain dry through the rest of the period. Strong northwesterly winds are expected to develop after 13Z and persist through the remainder of the period. Wind gusts will approach 25 to 30 knots. KMCW and KALO could see increasing and lowering CIGS between 13Z and 19Z as the surface's low backside low clouds move across northeastern Iowa.

DMX WATCHES/WARNINGS/ADVISORIES

None.