textproduct: Des Moines

KEY MESSAGES

- Breezy and dry this afternoon, with winds diminishing by this evening.

- Milder temperatures on Monday, but with a cold front pushing through in the afternoon and evening. A few strong to severe thunderstorms will be possible along the front late in the day across the southeastern half of Iowa.

- Cooler weather from Tuesday into Thursday, with another frost/freeze possible in parts of Iowa Tuesday night.

SHORT TERM /THROUGH TUESDAY/

Issued at 126 PM CDT Sun May 3 2026

A weak surface high pressure area is building into the area from today, heralded by a wind shift that has passed across most of our service area. Behind this boundary there is little sensible temperature difference, but winds are turning to northwest and increasing to 15-25 MPH with gusts of 25-35 MPH. However, these higher winds will only last for a few hours, as the combination of the high building in and diurnally diminishing low-level mixing will cause winds to go light and variable by around sunset, then come around to south southwest and remain light overnight. Meanwhile, temperatures have risen into the mid-60s to lower 70s this afternoon beneath mostly sunny skies, and with dewpoints remaining in the mid-30s to lower 40s. This has made for a glorious spring day for most outdoor interests. The dry and quiet weather will continue tonight as temperatures fall into the mid/upper 40s, prevented from falling much further by the light but organized south southwest breezes overnight.

By Monday morning a 500 MB shortwave trough will be moving across North Dakota and Minnesota, pushing a cold front southward toward Iowa. The front is expected to reach our northwestern areas near Estherville and Algona around noon or just after, eventually reaching our southeastern areas near Ottumwa and Centerville by Monday evening. The broadly cyclonic flow spreading aloft on the southern periphery of the passing shortwave will initially bring modest and nebulous forcing for ascent. However, late in the day and into the evening, slightly better forcing combined with diurnal destabilization will support gradually increasing shower and thunderstorm chances. Initially, it is likely that the advancing surface front will provide a focus mechanism for the first storms to develop in the late afternoon, likely in our eastern to southeastern counties where the boundary is expected to lie and where the preceding capping inversion will be weakest/erode earliest. This initial round of showers and storms should exit relatively quickly to our southeast on Monday evening, however, a subtle secondary shortwave moving overhead Monday night may support lingering overnight rain along the 925-850 MB frontal zone, if low-level dry air can be sufficiently overcome, resulting in lingering light rain chances over the southern 1/2 or 2/3 of our forecast area Monday night, exiting to the south on Tuesday. Behind the initial surface front, instability and moisture will be limited and severe weather is not anticipated with the later activity. However, during the initial round of storms along the surface boundary late Monday afternoon and evening, surface-based CAPE of around 1000-1500 J/kg is forecast, along with deep-layer (0-6 KM) bulk shear of around 30-40 KT. Low-level moisture will be lacking with dewpoints likely only in the 40s, however, forecast soundings indicate steep mid-level lapse rates and good low- level mixing supporting a modest threat of hail and gusty winds from any stronger updrafts. The SPC has outlined about the southeastern half of Iowa with a Marginal Risk, which is appropriate for this scenario.

LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/

Issued at 126 PM CDT Sun May 3 2026

Any lingering rain will clear out of southern Iowa on Tuesday as cool and dry air continues to filter in from the north. Temperatures will be notably lower behind the cold front, with daily highs only in the mid to upper 50s both Tuesday and Wednesday. Cyclonic 500 MB flow will persist aloft during this time, but any thought of rain chances is mitigated by the lack of available moisture or instability. Meanwhile, Tuesday night/Wednesday morning lows will fall into the 30s across much of Iowa once again, with near-freezing temperatures in the north, prompting another round of frost/freeze concerns at least in some areas.

A couple of more pronounced 500 MB troughs will move over later this week, from around Thursday onward, providing a return of low (20- 30%) PoPs at times, but no significant precipitation or hazardous weather is foreseen. Meanwhile, the surface pattern will become more erratic and diffuse in general, supporting a slow moderation of temperatures as highs return to the 60s on Thursday and Friday, and possibly some 70s by next weekend.

AVIATION /06Z TAFS THROUGH 06Z TUESDAY/

Issued at 1042 PM CDT Sun May 3 2026

VFR conditions prevail through much of the TAF period. Light and variable winds this morning will increase out of the southwest after sunrise. A front dropping north to south through the area will lead to increased winds and changing directions through the day. Winds become westerly just ahead of the front, then northerly behind. Winds will generally gust to around 20 to 25 kts, with sporadically higher gusts near 30 kts possible. A few showers and/or thunderstorms are possible along the front in the late afternoon and evening, but this threat looks to be primarily over KOTM and southeast. Winds remain breezy into the evening, before diminishing overnight.

DMX WATCHES/WARNINGS/ADVISORIES

None.