textproduct: Des Moines

KEY MESSAGES

- Another hot and humid day is in store for much of the state today with heat and humidity persisting through the 4th of July weekend.

- Storm chances return today with an Enhanced (Level 3 of 5) Risk clipping the northern fringe of the state and a Slight (Level 2 of 5) Risk extending farther south. Additional severe chances exist tomorrow with a Slight Risk (Level 2 of 5) for much of northern and central Iowa.

UPDATE

Issued at 943 PM CDT Tue Jun 30 2026

A few storms in southern Iowa have begun to develop early due to some deep moisture convergence and warm air advection. We expect these initial storms to remain sub-severe as they struggle against the cap due to limited forcing. However, as we progress into the overnight hours, a strengthening low-level jet will arrive, bringing the necessary forcing for strong to severe storms across northern Iowa tonight.

Due to the increase in storm potential and cloud cover across northern Iowa tonight into Wednesday, highs have been adjusted to the upper 80's. Heat indices will fall below the extreme heat warning criteria, so we replaced the warning with an heat advisory across NE Iowa.

SHORT TERM /THROUGH THURSDAY NIGHT/

Issued at 255 AM CDT Wed Jul 1 2026

Yet another hot and humid day is in store today. The Gulf remains open for business as southwesterly flow continues to feed moisture into the area. High temperatures across northern Iowa (north of Highway 20) have been bumped below 90 degrees. Yesterday's highs underperformed, particularly in the north where lingering cloud cover from convection remained through part of the morning. Expectations are for more of the same across northern Iowa, with lingering clouds from convective activity in the early morning that will keep highs slightly lower. That being said, dewpoints in the lower to mid 70s still lead to heat indices in the 90s statewide. With the (slightly) lower temperatures, western and northwestern Iowa no longer have heat headlines. Portions of northern and northeastern Iowa will remain under a Heat Advisory through today, with the rest of the state holding onto its Extreme Heat Warning. Going into tomorrow, heat headlines will be concentrated more into the southern and southwestern portions of the area as the high begins to shift slightly to the east.

Another thing to note for today is the chance for severe weather. SPC has an Enhanced (level 3 of 5) Risk for the far northern fringe of our area, with a Slight (level 2 of 5) Risk encompassing much more of the area. Severe parameters look to be lining up in the northern half of the area. Guidance suggests a warm front/stationary boundary will set up in the vicinity of the IA/MN border. The consensus is that this boundary will be on the Minnesota side, with some variability in how far north it sets up. An abundance of CAPE is available with MLCAPE values generally in the 2000-2500 J/kg range. Shear is looking much better compared to previous days, with 30-40 kts across northern Iowa according to deterministic guidance. The 00z HREF shows lower mean values across northern Iowa closer to 30 kts, while the 00z REFS ensemble is closer to 35 kts. Regardless, the best shear looks to be to our north and west. Coverage across Iowa/the CWA is still somewhat limited, though not as much as previous days due to the high beginning to shift. As far as hazards go, today's severe threat is mainly damaging winds and hail. D-CAPE values are on the order of 1500-2000 J/kg and mid- level lapse rates are a healthy 7 C/km across much of northern Iowa.

With the potential for repeated convective activity over the same general area and an abundance of moisture, mean PWAT values of 2 inches are being shown by the REFS and HREF. In addition to severe weather, flash flooding could become a concern over cities and towns going forward with repeated rounds of storms.

LONG TERM /FRIDAY THROUGH TUESDAY/

Issued at 211 PM CDT Tue Jun 30 2026

The center of the ridge will shift farther to the Middle Atlantic Coast by the start of the Fourth of July weekend with the flow becoming more zonal across the country. The airmass looks to remain sultry through Saturday, which may necessitate additional heat headlines, especially given the many outdoor activities and celebrations around Independence Day. There also looks to be more late afternoon and overnight storm chances Friday and Saturday with the latter potentially aided by a shortwave trough riding through the flow into Iowa Saturday night. However, specifics on any severe concerns, location, and storm timing are far too fuzzy at this time to detail. Precipitable water values and warm cloud depths will be seasonal to seasonally high with storms motions that look to be their slowest Friday night through Saturday night. This parameter space points to the potential for locally heavy rainfall. Flash flooding concerns are noted by WPC with a marginal risk of excessive rainfall each day from today/Tuesday through Saturday. This concern, at least at this point in time, would be highest over any urbanized area as NASA SPoRT soil moisture percentiles are at the 30th percentile or lower over northern Iowa through much of the western half of the state. However, there could be corridors, especially in northern and perhaps western Iowa, that are primed with rainfall before this weekend.

The zonal pattern will evolve into a ridge developing over the western US by late in the weekend into early next week as the shortwave trough moves away from Iowa. It will turn less hot Sunday into Monday along with lowering chances for storms behind the shortwave trough.

AVIATION /06Z TAFS THROUGH 06Z THURSDAY/

Issued at 1112 PM CDT Tue Jun 30 2026

Showers and storms are expected to be present in northern Iowa during the start of this TAF period. Confidence is medium that KFOD and KMCW will be impacted by the storms. Additionally, low-level winds will introduce LLWS at all terminals until sunrise Wednesday. Diurnal winds and cumulus fields will increase mid-to-late Wednesday morning with the return of daytime heating. As we near the end of this TAF period, another round of storms will be possible across central Iowa but confidence is too low on timing and location of the storms to issue PROB30 at this time.

DMX WATCHES/WARNINGS/ADVISORIES

Heat Advisory until 10 PM CDT this evening for IAZ007-016-017- 025>028. Extreme Heat Warning until 10 PM CDT this evening for IAZ035>039-046>050-058-071-081. Extreme Heat Warning until 10 PM CDT Thursday for IAZ059>062- 072>075-082>086-092>097.