It would appear that the recent non-stop rainfall events have finally relented with dry weather lasting into next week along with plenty of sunshine currently forecast. The lack of dry weather during September has certainly delayed the fall harvest season for Iowa. The featured chart presents USDA NASS soybean harvest estimates for Iowa. The NASS reports are weekly, so daily values are linearly interpolated between the weekly reports. The most recent report valid on this past Sunday estimated just 3% of Iowa's soybean acres as harvested. The left hand chart plots the yearly process numbers with the 3% value denoted each year. The right hand chart lists out those yearly 3% dates. Only a couple of years over the past 15-20 have been more delayed than this year. Things will likely not have improved much when NASS releases its next report on Monday as significant rains fell this week and we will need a number of days to dry out!

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The calendar has mercifully turned to October and after the rains end this morning, there is hope for a much needed upcoming stretch of drier weather. Will likely be able to create a number of daily features over the coming days denoting how remarkable the weather of this past September was. The featured chart today looks into daily average relative humidity as computed for the Des Moines Airport weather station. The top panel plots the daily observations along with the climatology which has been smoothed to remove the day to day noise. The bottom panel plots the smoothed frequency of having the daily average relative humidity above 90%. Around 10 days for 2026 are shown having an average relative humidity of 90% or greater, which works out to 33% of the days! The bottom panel puts the climatology around 5% of the days. High humidity and the lack of a killing frost are contributing to significant grain quality concerns as a mature crop continues to wait to be harvested.

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The persistent rains and frequent cloudiness this September have greatly reduced chances of early fall season cold weather. For Ames, the minimum season to date low temperature has been just 48°F last Wednesday. The featured chart presents the fall season minimum temperature by year through 30 September. The 2026 value is the warmest on record for the site over this period. Early season cold is certainly dependent on clear skies and dry air allowing efficient overnight cooling. Both of those have been sorely lacking throughout much of September. After we hopefully survive the ongoing deluge of rain this week, there is hope for better weather next as most of the state needs multiple weeks of dry weather to allow fall harvest to begin in earnest.

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A recent daily feature looked into the probability of Des Moines setting a new September Precip Record. At the time, the scenario based probability was only around 7% chance. Fast forward thirteen days and numerous rounds of rainfall later, Des Moines is within striking distance of both the September record and the all time monthly record. The featured chart presents the top ten monthly precipitation totals for Des Moines. The 2026 total currently stands in sixth place and 1.76 inches behind the September record and 2.74 inches behind the all time monthly record. Adding at least another inch to the 2026 September total over the next two days seems very certain as a major rainfall event is expected thanks to the remnants of Hurricane Polo. Adding another two inches is not as certain, but such totals and even higher will be common over more isolated areas within Iowa.

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The continued near daily rainfalls this September continued over the weekend with a number of rounds of light rainfall. The featured calendar chart presents daily precipitation reports for the Des Moines airport so far this September. Only two dry days are shown over the past two weeks and even only four over the past three weeks. More rain is in the forecast for this week as last few days of the month will take a run at attempting to set a September precipitation record for Des Moines (still need ~1.5 inches more).

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Last week, the featured plotting tool provided the chances of Des Moines setting a September record for precipitation. At the time, the scenario based chance was at 7% and an updated plot shows it at 1%. Today's featured chart looks into the chances of Ames setting a new yearly precipitation record. The chart appends historical observations onto the 2026 year to date total precipitation and then computes the percentage of those scenarios that exceed the 2010 record. Remarkably, only one previous year provided the 16 inches yet needed to top 2010. The featured plotting tool was recently extended to provide year long based scenarios and hopefully you find it useful for answering similar questions for other locations around the US.

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For most of Iowa, 2026 has been a rather wet year. Ames is not an exception with a current year-to-date total near 150% of average. One may wonder how anomalous daily precipitation events have contributed to such a large departure. The featured chart attempts to answer this question by first dividing up the period of record data into five bins with each contributing an equal precipitation volume. Those are the blue bars with the height representing the average number of such events per year. For example, ~50 daily events between 0.01 and 0.32 inches contribute as much precipitation as 2.3 events between 1.7 and 7.80 inches. The 2026 data is then placed into these bins with the red percentage values denoting how much above or below the bin contribution the 2026 value is. The chart shows how precipitation values greater than 0.65 inches have driven the large departure this year and even made up a small deficit for events between 0.32 and 0.65 inches.

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Tuesday was yet another rather dreary day with more rain and plenty of overcast cloudiness. The featured chart looks into the monthly frequency of overcast conditions as reported by the Des Moines airport weather station. There are number of caveats with long term comparisons of cloud coverage as techniques and instrumentation has changed over the years. That aside, the top panel shows the monthly max and min values along with a simple mean and actual 2026 observations for percentage of hours with the sky coverage being overcast. The bottom panel plots the yearly values for September. The 2026 value is certainly above average and about the fourth highest on record so far. Thankfully, a bit more sunshine is expected today before more cloudiness returns.

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The rainfall totals for September continue to amaze with today's feature denoting the largest seven day precipitation total by year for Waterloo. The top left panel shows the seven day period with the color representing the total. The bottom left panel shows the frequency of a given day of the year participating within this maximum period each year. The top right panel shows the yearly maximum value. The bottom left panel shows the cumulative distribution. The 2026 value is currently 4.46 inches ending on 20 September. The bottom left panel interestingly shows these events being more frequent during September than during August for the site! September is even comparable to the climatologically wetter months of May, June, and July.

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The parade of heavy rainfall events this September continued over this past weekend with the highest totals found over eastern Iowa. The featured map presents the combination of NOAA MRMS 48 hour estimates ending 7 AM Sunday with available NWS and CoCoRaHS reports overlaid. There are a number of stripes of rainfall ranging between five and seven inches. Thankfully while more rain is in the forecast, intense totals like those plotted do not appear possible. Temperatures will be cooler as well and much more fall like. A side note that unfortunately an IEM plotting tool does not yet exist to generate maps like the featured one today.

The featured chart is perhaps "Exhibit A" as to why Iowa continues to see heavy rainfall events this September. The chart shows average precipitable water during the month of September based on evening soundings from the Omaha area. This value represents the amount of water within the atmosphere and is expressed by a depth (plotted in millimeters). You can sort of think of the value as the amount of rain that would fall if all of the water was squeezed out of the atmosphere. While the 2026 value still has two weeks of time to pull the average lower, the plotted value is well beyond any previous September on record for the site. Storms that develop within an atmosphere loaded with water vapor are able to efficiently produce rainfall due to limited dry air and typically warmer cloud depths. Multiple rounds of such storms are expected on Friday and into the weekend.

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After the very hot start to September, temperatures have become much more fall like and it has recently felt more like fall. The actual start of the fall season is subjective with some claiming 1 September, others claiming the Tuesday after Labor Day, and others the fall equinox date. The featured chart attempts to take a statistical approach to access the date when the trailing 91 day average temperature starts to decrease. This effectively denotes a 91 day period with the warmest average temperature for the year. The middle subplot provides the date each year for Ames that this 91 day period ended. A simple average puts the date at 6 September, which is conveniently when this period ended this year. The bottom plot extends this algorithm then to consider the duration from the end of summer to the start of the winter season (coldest 91 day period). The average number of days is just 85.5, which implies our fall season is about a week shorter than an equitable season should be! There is certainly much variability with some fall seasons shown to last less than 60 days and others over 100!

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The precipitation totals for September continue to pile up as daily rounds of storms frequent the state. For Des Moines, the September 2026 total now stands at 10.52 inches and is the second largest total on record during the month of September behind 14.81" during 1914. With half of the month to go, it would seem "easy" to break this record, but the featured chart tells another story. The chart plots the accumulated precipitation total for 2026 (red line) and 1914 (black line). The tan lines represent the appending of previous year's 16-30 September data unto the 2026 time series. This effectively provides potential scenarios for where the 2026 total could end up. Using this method and remarkably, only 7.4% of previous years would push the 2026 total to a record value. The main issue is that the 2026 total is still 4.3 inches short of 1914 and that total in itself would be extreme for the last half of September. Climatology is also working against larger precipitation totals by the day as the atmosphere continues to cool and hold less water vapor. Having said all of that, the forecast looks to bring another two inches, at least, for the remainder of the week. So stay tuned!

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Monday saw a number of rounds of rainfall to start off what looks to be a very wet week. The featured chart looks into the number of distinct hours per month with the automated weather station reporting some form of rain (RA METAR code). Note that this is not exactly a total number of hours with rain as individual reports cover a shorter duration of time than one hour. The chart is still quite informative and tells an interesting climatology story for Iowa. The blue bars are simple averages since 1973 (the modern observation era). It is interesting to see July with the lowest average among the months stretching from March through October. The reason is that storms are much less organized and more isolated than other months, so while they do produce significant rainfall totals, the overall duration decreases vs larger scale precipitation events. The 2026 observed values are shown by the red bars and the September total is well on its way to finish above average with half of the month yet to go.

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A remarkably wet week of weather is forecast over the Midwestern US. The featured map presents Weather Prediction Center forecast precipitation over the next seven days ending Sunday evening. Most of Iowa is shown at three inches and higher accumulations over this period. The regions plotted in black are over seven inches for this period! This forecast "paints" precipitation with broad brush strokes, so locally much higher amounts are anticipated over more isolated locations. This week will certainly put the breaks on any fall season harvest progress as it appears no locations within Iowa will avoid significant rainfall.

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With high temperatures on Friday expected to reach the lower 80s for much of Iowa and a handful of days over the coming week as warm, it is a good time to check in on the number of days per year with a high temperature of at least 80°F for Ames. The side tables list the top 10 years with the most and least number of days. The bars are colored by their departure from a simple period of record average (black line at 91 days). The 2026 total hasn't quite breached the top 10, but is already well above most years over the past two decades. It is also the seventh consecutive year above average.

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Yesterday's daily feature presented a 24 hour precipitation estimate with reports overlain over the Des Moines Metro showing a stripe of 5 to 6 inches over southern Polk County (Des Moines). One of the observation locations within that stripe was the Des Moines Airport. The weather station there recorded 3.77 inches on Tuesday (a daily record) and 2.12 inches on Wednesday making for a two day total of 5.89 inches. The featured chart presents the largest two day precipitation totals for Des Moines and shows the most recent event coming in fourth largest on record and the largest total since the 1970s.

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It has been quite the year for big rainfall events over the Des Moines metro area. Last night's event brought severe thunderstorms to the metro area with intense rainfall rates leading to flash flooding. The featured map combines NOAA MRMS 24 hour precipitation estimates ending at 7 AM with NWS and CoCoRaHS reports. A stripe above five inches is shown across southern Polk County (Des Moines). Previous and similar IEM feature maps include 4 July and 21 July.

While still humid, temperatures did cool off a bit on Sunday into Monday with a number of locations experiencing the first sub 70°F temperature reading of this September. For Des Moines, the low on Labor day was 67°F (hi kids), which was the coolest reading over the first seven days of September. The featured chart presents the coolest low temperature over the first seven days each year on record for Des Moines. Remarkably, four other years had experienced a warmer minimum over this period including 2015. Plenty of warm days are forecast for the shortened work week before perhaps cooler weather arrives for the following week.

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It has been a very hot and humid start to September with high temperatures again soaring into the 80s and 90s for Iowa on Thursday. For Des Moines, the first three days of the month have had a high temperature of at least 95°F. The featured chart looks into the frequency of a given day of the year participating within a streak of at least as much days with such a warm high temperature. The earliest and latest streaks are listed off to the side. There have been later streaks into September on record, so this current one isn't exceptionally rare. The hot weather will continue into the Labor Day weekend with only slightly cooler weather expected next week, but still well above average.

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