textproduct: Des Moines

KEY MESSAGES

- Temperatures cool near freezing over northern Iowa tonight into Monday morning. A Frost Advisory will be in effect.

- Shower and storm potential returns through late Monday night into Tuesday. A few stronger storms could develop in southeastern Iowa on Tuesday afternoon, with gusty winds being the main concern.

- Breezy conditions also expected throughout the area on Tuesday, with the strongest winds in northern Iowa. Sustained winds of 25 to 30 mph, with gusts up to 40 mph.

- Warmer temperatures expected through the week and into next weekend.

SHORT TERM /THROUGH TUESDAY NIGHT/

Issued at 248 PM CDT Sun May 10 2026

The weather over Iowa has certainly shown out for Mother's Day today. Dry conditions prevail over Iowa, with sunny skies and temperatures in the mid to upper 60s this afternoon. The exceedingly dry low levels and steep low level lapse rates have led to breezy conditions across northern Iowa, where gusts are once again exceeding the 90th percentile of the NBM guidance today. Surface observations at Mason City and Estherville have shown peak gusts around 35 to 40 mph this afternoon, although these are on the high end, while the broader wind field has been gusting closer to 25 to 30 mph. Winds will diminish shortly after sunset, becoming light to calm overnight as the surface ridging continues to move in.

With the surface high overhead, expect light winds, clear skies and temperatures to plummet over northern Iowa tonight into Monday morning. Last nights lows cooled 2 to 4 degrees below the forecast yesterday, which had already been nudged a degree or two cooler than NBM guidance. Tonight, with cooler air and similar conditions, have elected to push lows toward the 10th percentile of NBM guidance, which brings low temperatures near freezing by Monday morning. With dewpoints in the upper 20s, would not be surprised if some areas even dipped below 30, especially in valleys or low-lying areas. Given the temperatures nearing freezing and frost potential tonight, have issued a Frost Advisory for tomorrow morning where the coldest temperatures are anticipated across northern Iowa. Other areas of the state could also see patchy frost develop as temperatures dip into the low to mid 30s, namely portions of the Nishnabotna Valley, but mid-level cloud cover over central into southwestern Iowa should limit radiational cooling for these areas through at least a portion of the night.

Southwesterly winds on Monday will bring warmer return flow up into the state, boosting highs back into the 70s during the day. Dry conditions are expected Monday before another shortwave dives southeastward through the upper midwest Monday night into Tuesday. The main wave, and coincident forcing, looks to stay to our northeast across Minnesota and Wisconsin, but the synoptic lift does clip the far northeastern portions of Iowa. This, in combination with an increasing gulf moisture stream into the state, will introduce the potential for some showers and even a few storms on Tuesday.

That said, there are still a few question marks with this system's passage. The rate of moisture return seems questionable among guidance, with some models struggling to saturate the layer and producing little to no QPF, even in the northeastern portions of the forecast area where forcing is best. Moisture availability is slightly better farther south and west into central and southern Iowa, but forcing is weaker in these areas. There will be a weak boundary/trough moving through the state, but convergence along it looks meager, limiting the amount of forced ascent outside of what's tied to the main wave. These factors are leading to very low probabilities being output by NBM, both in northeastern Iowa where forcing is best and in areas farther south and west in central and southern Iowa along the boundary. However, looking at grand ensemble output (GEFS, ENS, & GEPS), the probability of 0.01" or more of precipitation is 60 to 80% over northeast Iowa, much higher than the 20 to 30% in NBM. All this to say, guidance is clearly struggling with this setup, but the signal is there for at least scattered showers in the area Tuesday morning, with even a few storms possible in southeastern Iowa before the surface front pushes through. The timing isn't ideal for severe thunderstorms in most of our area, but some destabilization ahead of the front may lead to a few stronger storms. Winds will be the primary concern, especially with the dry low levels. Of course, this will be contingent on enough convergence to displace parcels and overcome any capping in place Tuesday afternoon.

Greater certainty resides in the wind potential on Tuesday, as increased wind fields around this system result in gusty winds on Tuesday. NBM seems to have a pretty good handle on winds based on model soundings, depicting sustained winds over northern Iowa around 25 to 30 mph, which would be approaching wind advisory criteria.

LONG TERM /WEDNESDAY THROUGH SUNDAY/

Issued at 248 PM CDT Sun May 10 2026

Temperatures cool slightly on Wednesday, albeit still in the 70s. The broad upper level ridging then fills in behind the departing shortwave, warming temperatures into the 80s through the second half of the work week. As mentioned in yesterday's long term discussion, despite the brief ridge moving in, the pattern quickly becomes agitated through the end of the week and into next weekend with multiple shortwaves and increasing shower and thunderstorm potential, the first of which looks to be on Thursday night into Friday as a healthy gulf moisture stream returns to the state. Additional chances continue into the weekend. This will likely put a damper on the highs in the 90s that NBM guidance had been forecasting for next weekend and today's extended forecast now reflects this a bit better. That said, with the southwesterly to westerly flow pattern, temperatures should stay seasonably warm in the 80s through the weekend.

AVIATION /00Z TAFS THROUGH 00Z MONDAY/

Issued at 619 PM CDT Sun May 10 2026

VFR conditions are expected to prevail through this TAF period. Patchy VFR cumulus is expected to dissipate shortly after sunset, leading to clear skies through the night. Winds are currently from the northwest at 10-15kt, gusting from 20-25kt, but will become light and variable after sunset and will remain light through the TAF period. A surface high will move across Iowa, leading to a gradual wind shift throughout the period. Shortly after this TAF period, winds will be light and become from the south as the high clears the region.

DMX WATCHES/WARNINGS/ADVISORIES

Frost Advisory from midnight tonight to 8 AM CDT Monday for IAZ004>007-015>017-025>028-039.