textproduct: Des Moines

KEY MESSAGES

- Low (20-40%) chances for showers and thunderstorms are forecast in the afternoon and evening both today and Friday. The threat of severe weather or widespread rainfall is low.

- More substantial (60-90%) and widespread rain and thunderstorm chances are forecast Saturday night and Sunday. There may be some risk of severe weather mainly in southern Iowa. There is also potential for heavy rain and localized flooding, mainly in the southern half of Iowa.

SHORT TERM /THROUGH SATURDAY/

Issued at 212 PM CDT Thu Jun 18 2026

From this afternoon through Saturday, Iowa will reside beneath relatively benign west northwesterly 500 MB steering flow. This will translate into a fairly nebulous surface pattern, with alternating weak troughs and ridges and generally light breezes of varying direction. Temperatures will also remain pretty steady from day to day, with highs in the mid-70s to lower 80s each afternoon and lows in the 50s to lower 60s each morning. The precipitation forecast is a bit more interesting, however. Later this afternoon and evening a subtle shortwave impulse will move overhead, focused more in northeastern Iowa and adjacent states, and combined with the diurnal heating maximum should provide sufficient impetus for convective initiation. The coverage and latitudinal extent of any resulting showers and thunderstorms is unclear, however. Earlier short-range model runs depicted only isolated coverage mostly confined to our northern and northeastern counties, however, new data this morning has indicated more scattered coverage extending perhaps all the way down to the Missouri border. In light of this, have expanded 20-30% PoPs across most of our area for a few hours later today, keeping only our southwestern and far southern counties at 10% with no rain mention. In any event, weak low- level flow and meager instability will preclude any severe weather threat, so the only sensible impacts from any convection that does occur will be brief rain and a few rumbles of thunder.

After quiet and dry conditions overnight and Friday morning, another, somewhat more energetic shortwave will approach our area from the northwest later on Friday. Once again the approach of this system will be coincident with maximum diurnal heating/destabilization, but this time around the broad forcing for ascent associated with the wave is somewhat more pronounced, and atmospheric moisture is also much higher with forecast soundings showing a few hours of near-saturation in the mid- levels. In our northern counties this near-saturation extends down to the surface, but in our central and southern counties it may still be undercut by a dry layer in the lowest 5000 FT or so. Nevertheless, the coverage and duration of rain chances will be higher Friday afternoon and evening, and have increased/expanded PoPs as a result with ~40% now included in our north, and ~20% PoPs extending southward to the Missouri border by Friday evening. Despite the expectation of higher precipitation coverage/chances, instability will remain low and severe weather again is not anticipated. Pockets of relatively heavier rainfall could occur given the greater degree of available atmospheric moisture, but not of sufficient magnitude or area to prompt any hydrological concerns.

In wake of the late Friday system, we will experience another brief dry and quiet weather period from late Friday night through much of Saturday. By late in the day Saturday some additional showers/storms could occur, but for the most part these should hold off until Saturday night, as discussed in the Long Term section below.

LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/

Issued at 212 PM CDT Thu Jun 18 2026

By Saturday afternoon, a 500 MB trough will be moving over the Rockies and approaching the High Plains. The vorticity embedded within this trough will be split into at least two distinct shortwaves, the first of which will move across Nebraska and northern Kansas Saturday night, and Iowa on Sunday. As this system approaches on Saturday, broad surface low pressure will develop over the southern High Plains, while a surface high pressure ridge over the Upper Midwest steadily retreats northeastward away from Iowa. By midnight Saturday night, the surface trough will coalesce into a trough somewhere around southwestern kansas, with an effective warm front extending east northeastward along or near the Iowa/Missouri border. Deep and persistent moisture transport ahead of the system will result in significantly increasing PWAT values across the region, such that by 12Z Sunday PWATs will approach 2" in far southern/southwestern Iowa, which is well above normal for the season. While there is some disagreement among various deterministic models in the details of convective evolution, it does appear likely that some type of thunderstorm complex will form over southern Nebraska or far northern Kansas Saturday evening, then spread eastward or east southeastward along the frontal boundary. This complex may affect our southern counties Saturday night, or may remain farther south across Kansas and Missouri. Meanwhile, north of the boundary widespread rain will develop across most or all of Iowa, as broad forcing for ascent ahead of the approaching shortwave meets deep available moisture and modest elevated instability in place across Iowa. By late Saturday night and into Sunday the current forecast calls for PoPs of around 60% in our north to near 100% in the south.

While rain is likely to a near certainty from late Saturday night into Sunday, the associated threats are somewhat less clear. Given the time of day, saturated atmospheric column, and limited instability north of the aforementioned warm front, the severe weather threat should be generally low across Iowa. An exception to this is in far southern Iowa, where depending on the location of the front and track of the associated thunderstorm complex discussed above, there may be a threat of strong winds if the forecast trends northward and sufficient near-surface instability is introduced. Aside from severe weather potential, the more growing concern at this time is the possibility of heavy rainfall and localized flooding. Deterministic guidance paints generally 1.5-3" or so of QPF across the southern half of Iowa from midnight Saturday night through the day Sunday. However, much of the deterministic guidance is at the higher end of the ensemble envelopes. For example, the deterministic NBM depicts 2.2" of QPF at Des Moines and a maximum of 3.0" in Taylor County, however, it also indicates only a 20% chance of exceeding 3.5" at Des Moines and a 35% chance along the Iowa/Missouri border. This indicates that while substantial rainfall is likely, very high or extreme amounts are less likely than might otherwise be expected. In addition, for most solutions within this general scenario, the rain should be of a longer-duration, which those amounts (if they even occur) falling over the course of 18 hours or so, rather than in a short burst, which lowers the flash flooding threat. The season also raises the bar for rainfall intensity/amount needed to get a response, due to the peak state of most crops and vegetation at providing capacity. Finally, in terms of river flooding, if the heaviest rain does fall from southwestern into southern Iowa, it will be near the state divide an in smaller basins that quickly drain out of the area, somewhat limiting the river flooding threat. All that being said, these concerns will be closely monitored over the next couple of days, as the forecast could easily shift more toward a more northern and/or heavier rain solution, or toward a more southern and/or less heavy rain solution. If the more northern/heavier rain solution verifies, then we could see heightened flooding/flash flooding concerns in some parts of our southern and even into central areas.

The weekend rain/storm system will gradually push off to the east later Sunday, after which forecast confidence decreases rapidly. This is primarily due to the evolution of the second shortwave within the larger 500 MB trough as mentioned earlier, which long-range models are not handling well in terms of consistency between models or from run to run. The result is persistent low to moderate (10-50%) PoPs in the first half of next week, with a continuation of near to a little below normal temperatures. Looking into the way-out machine, it does appear a large 500 MB high pressure area will become established over the southwestern U.S. by the latter half of next week, with a ridge extending up along the Rockies. If this ridge remains shunted somewhat southward and Iowa lies beneath broad cyclonic flow to its northeast, then seasonal temperatures and intermittent rain chances would be likely to continue. On the other hand, if the ridge exerts its influence farther northward, and the cyclonic storm track is pushed northeast of Iowa, then it could favor gradual warming and a somewhat drier forecast. We will see how this plays out as we have several more pressing systems to get through before then.

AVIATION /18Z TAFS THROUGH 18Z FRIDAY/

Issued at 1214 PM CDT Thu Jun 18 2026

VFR conditions will prevail through the TAF period. Widely scattered SHRA/TSRA are forecast later this afternoon into early evening. Coverage and anticipated impacts are too low for TAF mention however, except at MCW where probability is highest (~30%), and even there have advertised just VFR in TSRA due to a much lower (~10%) chance of brief MVFR or lower visibility occurring.

DMX WATCHES/WARNINGS/ADVISORIES

None.