Derby, IA 50068 Weather

: Updated for the 00z Aviation Discussion:

Key messages

- Scattered showers and storms this afternoon (30% chance) mainly in northeast Iowa.

- Marginal Risk for severe storms later this afternoon, mainly in northern and northwestern Iowa. Large hail is the main threat followed by a very low chance of damaging winds.

- Rain returns Friday and chances remain for much of the remainder of the forecast. High temperatures challenged by rain and persistent cloud cover.

Short term

Issued at 238 PM CDT Wed Oct 28 2026

A closed midlevel low in southern Canada enhanced the synoptic winds across the Upper Midwest this afternoon. The strongest flow is north of Iowa, meaning deep-layer shear is lower compared to our neighbors in Minnesota. Low-level moisture is increasing ahead of an approaching cold front. Dew points in the low 60s were collecting in western Iowa. Scattered showers and a few storms populated the state ahead of the front. These reside along the instability axis, roughly along the MUCAPE = 1000 J/kg contour.

For the severe weather risk today, the threat will be short lived with most of the storm activity in Minnesota where the kinematic and thermodynamic parameter spacing is better. Low level hodographs will loop with the increasing LLJ, increasing SRH over Iowa. Northern Iowa will have the highest severe risk this evening as they have marginally better deep-layer shear and better convergence along the front. Due to the presence of clouds today, capping looks to inhibit storm development and reduce the wind and tornado threat in Iowa to under 2%. The CAPE distribution is also elongated in the profile and the lapse rates are weak (<7 C/km) so parcel acceleration and updraft strength are slowed. The resultant storm mode will be a broken line of storms with some of them early on (before sunset) utilizing the SRH to become supercellular. Hail growth in supercells will be most likely to become severe, aided by most of the CAPE residing in the HGZ and minimal below. Can't completely rule out damaging winds in this early window, especially close to the IA-MN state line. As we lose daytime heating, the SRH will become inaccessible by storms with time and the remnant scattered storms will have lightning and isolated hail. Low freezing level heights make hail growth easier to achieve, but the low deep-layer shear will make hail growth and storm lifespan abbreviated.

The front will exit and sag south of the state through the night and set up for a cooler Thursday. Lingering cloud cover in southern Iowa will challenge the 70 degree highs locally forecasted. Southwest flow recovers in the midlevels and a southern stream shortwave in the Desert SW will negatively tilt into the Plains, ushering in a return of rain for Friday.

Long term

Issued at 238 PM CDT Wed Oct 28 2026

A complex, amplified upper air pattern will dictate the extended forecast. Rain chances will loom for much of the period, including through the weekend to start. Timing differences still remain for Saturday on when precipitation will pause, but for now, it appears a warm front will lift northward towards Minnesota through the day, but there is enough uncertainty in remaining moisture to warrant keep a ~30% chance of rain in the area for Halloween night. Lee cyclogenesis will temporarily pull away moisture from the area Sunday, but it will return with a large closed system to start next week. Location of the warm sector is still uncertain as the formation of the closed low involves the combination of a couple component waves merging together. What can be said is the resultant feature will become wound up in the central US and will result in an extended period of rain chances, cloud cover, and cooler temperatures for the first week of November. It's possible that highs next week don't reach 70 degrees for the area.

Aviation

Issued at 639 PM CDT Wed Oct 28 2026

A broken line of thunderstorms will move across central Iowa this evening. These storms will be mostly past KFOD/KMCW by the start of the period while still impacting the other sites this evening. A band of MVFR stratus is expected to move into Iowa overnight and may persist into Thursday morning over the eastern sites. Southerly wind may be breezy to start the period then the wind will turn more west then northerly overnight into Thursday. Expect VFR conditions to be widespread by Thursday afternoon.

Watches, warnings and advisories

None.