Des Moines forecast discussion

Short Term /Through Saturday Night/

Issued at 107 PM CDT Thu Oct 22 2026

A large surface high pressure area has consolidated over the Great Lakes region today, even as a broad low pressure trough develops over the northern High Plains in the lee of the Montana/Wyoming Rockies. Iowa lies under the influence of the Great Lakes high, with sunny skies and light south southeasterly breezes providing a warm and resplendent autumn day once again. Meanwhile, at 500 MB, an elongated thermal ridge is building from northern Mexico up across the central CONUS and toward Hudson Bay. Concurrently, a deep 500 MB trough has come ashore over the Pacific coast, with a northern component reaching British Columbia and a southern component over California.

Over the next couple of days, the western 500 MB trough will attempt to progress across the continent but will be partially blocked by the preceding ridge. This will cause the northern component of the trough to slide northeastward over the top of the ridge, crossing Montana and North Dakota on Friday night and swinging up into central Canada on Saturday. As this occurs, the southern component of the trough will be abandoned over the southwestern U.S., eventually meandering toward the Four Corners region on Saturday night. Within this evolution, associated changes in the surface pattern will have sensible weather effects in Iowa. On Friday and Friday night the High Plains surface trough will sharpen and deepen with the passage of the northern stream 500 MB trough, eventually pushing into the eastern Dakotas and Nebraska as an effective cool front late Friday night. From late tonight through Friday some showers will develop in this region, where broad forcing and moisture advection on the periphery of the mid-level trough overlie modest surface convergence and moisture pooling along the boundary. However, this rain is expected to remain just northwest of our area and the forecast remains dry. With the approach of the surface trough and the weakening/eastward retreat of the Great Lakes high, a tighter pressure gradient will bring breezier conditions to our area on Friday, with speeds of around 15-20 MPH in our northern and western counties and gusts to around 30 MPH. This may lead to some marginally elevated fire weather concerns, but these will be mitigated by minimum RH values generally in the 35-40 percent range on Friday afternoon. Of more widespread interest will be the continuation of unseasonably warm weather for the next few days, with highs mostly in the mid to upper 70s both Friday and Saturday.

By Saturday morning the northern stream 500 MB trough will have passed by, while the remaining southwest U.S. trough will still be far away leaving Iowa beneath uneventful southwesterly mid- level flow. This will leave the surface trough stranded somewhere over the Upper Midwest, as it will be oriented parallel to the steering flow, with persistent shower activity occurring in the frontal zone by Saturday night. The question is where precisely the resulting swath of showers will be located. Various model solutions place it anywhere from just to the northwest of our forecast area to nearly central Iowa (again, in a southwest-to-northeast orientation). The most likely solution would seem to be a slight rebuilding of the 500 MB ridge during this time frame, nudging the boundary/rain toward the more northwesterly solutions and perhaps just clipping our service area up around Estherville, Algona, etc. In any event, instability will be very limited and only intermittent showers are anticipated within the swath, with no hazardous impacts.

Long Term /Sunday Through Thursday/

Issued at 107 PM CDT Thu Oct 22 2026

On Sunday and Monday the southwestern U.S. 500 MB trough (discussed in the short term section above) will finally drift slowly northeastward toward the central U.S. Even as this occurs, a stronger cyclone will come ashore over the U.S. Pacific Northwest coast. The leading trough will gradually wash out as it moves over Iowa sometime around Monday night or Tuesday, but the details of that evolution remain fuzzy at long range. Have maintained rain chances Monday into Tuesday across most of our area, but it remains to be seen how far in from the northwest the surface trough/rain will be able to penetrate during this time. We are likely to see a sharp temperature gradient across Iowa on Sunday, with the far northwest being cooler in clouds and showers where temperatures will probably peak in the 50s, while in the south and east sunny and warm weather will persist for another day with highs well into the 70s. This may also occur to some extent on Monday, but confidence in temperatures is low that day due to the uncertainties in location/timing of the surface trough, clouds, and rain. Once the leading 500 MB trough passes, there will be a brief respite with weak mid-level ridging before the stronger trough from the Pacific Northwest swings through our region in the middle of next week. That system will push a stronger surface trough through and sweep out most remaining moisture from the earlier systems, bringing quieter autumn weather for at least a couple of days afterward.

Aviation /00Z Tafs Through 00Z Friday/

Issued at 623 PM CDT Thu Oct 22 2026

There is high confidence in VFR conditions prevailing through the period at the terminals. High and mid-level clouds will increase on Friday over northern Iowa as winds from the south turn breezy by late morning through the afternoon. Sustained winds above 12 knots will be over the western half of the state during this period with gusts of 20 to 25 knots common as well.

Dmx Watches/Warnings/Advisories

None.

SHORT TERM...Lee LONG TERM...Lee AVIATION...Ansorge