textproduct: Des Moines

KEY MESSAGES

- Cool today through Friday with highs in the upper 50s to low 60s. Overnight lows will be in the 40s.

- Spotty showers move into the area on Thursday, becoming more widespread showers and thunderstorms Thursday evening and Friday. Severe weather is unlikely.

- Warming trend this weekend with a return to the 80s. The forecast is dry from later Saturday through early next week with precipitation chances returning late Tuesday into Wednesday.

SHORT TERM /THROUGH THURSDAY/

Issued at 238 AM CDT Wed May 20 2026

Very patchy early morning fog has developed in parts of northwest Iowa where high cloud have cleared out and temperatures have cooled to near the dewpoint. Widespread fog is not expected this morning, but shallow fog may develop in low lying areas through sunrise. Temperatures falling off quickly behind the clouds to create this patchy fog development is also the area we are watching for frost potential early this morning. Temperatures in far northwest reaches of the area are around 38-41 degrees and have reached their dewpoints. It is possible temperatures fall another degree or two through the morning, but with only a handful of sites skimming the upper 30s frost is not expected to be widespread.

It will be another cool day today with high pressure keeping warmer air well south of the state. At the same time, a long wave trough is developing across the western US. This will slowly move west, with the first indication being high clouds filtering into Iowa this afternoon. Temperatures remain chilly on Thursday in the low 60s. That trough will shift east with two embedded vorticity maxes. The southern vorticity max begins to lift into the area on Thursday morning but will battle dry air, resulting in spotty precipitation across the area in the morning to afternoon. The northern vorticity max with upper level trough axis swings across the area later Thursday and on Friday, providing the next chance for showers and a few thunderstorms across the area, as outlined below.

LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/

Issued at 130 PM CDT Tue May 19 2026

By Thursday evening a 500 MB trough will be moving over the U.S. Rockies, and will subsequently become negatively tilted as it emerges over the northern High Plains Thursday night and Friday. As this trough swings across the region, it will generate a broad swath of rain associated with surging moisture, increasing winds aloft, and modest theta-e advection. This swath will enter our southwestern counties Thursday night and move across our forecast area on Friday. Instability will be very limited with surface temperatures only in the 50s to lower 60s, but will still be sufficient for a few elevated thunderstorms at times though severe weather will be unlikely. The rain will move out to the northeast late Friday, after which one last lobe of vorticity clearing out the larger-scale trough will cross Iowa late Saturday. Moisture will be much more limited and it remains to be seen whether any additional showers or thunderstorms will occur in association with that feature. For now 70-80% POPs are carried across Iowa Thursday night into Friday, with only 10-20% POPs on Saturday.

In the first half of next week, from around Sunday to Wednesday, a large thermal trough will build over the central U.S., as a blocking pattern sets up with a large 500 MB low forming over the western U.S. Synoptically this would tend to support significantly warmer and generally dry weather for our region. However, there will initially be a week 500 MB trough/low over Texas as the larger ridge begins forming on Sunday, and long- range models are at odds with how that feature will interact with the ridge. The EC and GEM essentially wash out the low as it is overwhelmed by the larger thermal ridge, however, the GFS maintains it as a discrete feature that becomes trapped in the ridge and advects slowly northward over Iowa early next week. This leads to rapidly decreasing confidence in forecast details in the outer periods, however, even in the GFS solution generally warmer temperatures would still be favored, and it seems a safe bet that the cool weather of today and the next several days will be broken as we head into next week.

AVIATION /06Z TAFS THROUGH 06Z THURSDAY/

Issued at 1123 PM CDT Tue May 19 2026

VFR conditions will prevail at all terminals through the TAF period. Winds will be light from the northwest overnight before gradually shifting to becoming from the east by the end of the period, with wind speeds under 10kts at all sites. Skies will remain mostly clear through about 20z Wednesday, before a weak system will bring cloud bases down to FL120.

DMX WATCHES/WARNINGS/ADVISORIES

None.