Chilly weather is finally arriving to close out this week with temperatures below freezing expected for some by Friday night into Saturday morning. Up until this upcoming event, chilly weather was practically not existent as shown by the featured chart. The chart presents the accumulated season to date coldest low temperature for Ames. The blue line represents the 2026-2027 cold season with values found near the top or above the historical range. The black line shows the simple period of record average and indicates the average first freezing date is about last week, so Iowa avoided any early frost by a wide margin this year.

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The past few days have seen numerous record high temperatures either tied or set across the Midwestern US. Cedar Rapids, for example, tied their record high on Monday at 88°F with the previous record set in 1995. The featured map takes a look into the percentage of days with a high temperature record occurring over more than just one year. Rewording, the percentage of days with ties present. This is based on long term climate sites tracked by the NWS. There are some local quirks with some stations having a longer period of record and thus a higher chance of having ties, but the overall spatial trend is rather clear. The moderating effects of higher humidity levels and nearby bodies of water help to tighten the range of possible temperatures and create a higher chance of generating ties. High temperatures are more variable further inland with the lowest frequencies found over the most continental areas of the northern High Plains.

Monday was another very warm October day with a number of locations at or near record high temperatures. With a high of 87°F, Burlington set a new daily record besting the previous record of 86°F set in 1956. The featured chart looks into the year where the present day record lies by day of the year. The dots show the year of the daily record with any ties both plotted. The right side bar charts total up the record counts by decade. The colors represent the age of the record. The upper left panel shows the record daily high temperatures and the lack of recent such records during the summer months is readily apparent. The next panel shows the opposite situation with plenty of record maximum warm low temperatures being recently set over the past few decades and during the summer months. Tuesday will be a bit cooler, but still plenty warm for mid October!

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The weather is now fully cooperating to help with the fall harvest with plenty of sunshine, very warm temperatures, and a drying breeze. For Sioux City, after setting a record high temperature of 93°F on Saturday, a record high temperature was tied on Sunday at 91°F. The featured chart looks into the frequency of having a two day stretch with a high temperature of at least 91°F over those two days for Sioux City. The right hand side tables list out the end dates of the earliest and latest such two day periods on record. This past weekend comes in second latest behind a two day later event back in 1975. Monday will be another very warm day with record high temperatures again possible.

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The strong storms that developed early Thursday evening over Iowa were a bit of a forecast surprise with only very late runs of various forecast models depicting a possible robust environment to produce elevated thunderstorms capable of large hail. The NWS issued a number of warnings for the event and got hail reports to verify those warnings. The featured chart looks into the time of day frequency of having Severe Thunderstorm Warnings during the month of October. The chart presents the time of day frequency for Des Moines with the overall frequency plotted in tan and the values for October in blue. Of course, there are much fewer events during October so the plot gets a bit noisy vs the smooth full year values. Having such warnings during the night time is certainly more common than during the day as processes like the nocturnal "Low Level Jet" help fuel thunderstorms overnight.

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After a very wet September delayed harvest progress, the weather has done a full turnaround with near ideal conditions after the rains stopped on the first of October. The featured chart looks into the frequency of a given day of the year participating within a streak of at least seven consecutive days with a precipitation total below 0.01 inches. Note that this threshold sweeps the long term complexity of how trace amounts are handled as the minimum accumulation possible is 0.01 inches. Rewording, no measurable precipitation would include trace reports and thus be considered "dry weather" for this chart. The frequency of these events do increase as the fall season progresses and the chart nicely shows the clear annual signal. Iowa's current stretch of dry weather may be briefly interrupted for some with scattered light rain later on Thursday and into Friday morning expected, but coverage and amounts will not be significant. More robust rainfall chances will return later next week.

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After the rains ended on the first, the weather has thankfully turned drier this October and now warmer with high temperatures on Tuesday well into the 70s and even lower 80s for some. Des Moines hit 81°F, so the featured chart checks in on year-to-date accumulated days with a high temperature of at least 80°F. The green line shows the 2026 accumulation and back during early June, this year was not far off the record pace set by 2012. The few warm days during September has brought the accumulation closer to a simple long term average than the record total. The tan lines show each previous year on record and the intermittent jumps during October show how fleeting these days are this month and how rare they are by November. A couple more such days appear likely over the coming seven days, so try to enjoy them while they last!

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Our just finished month of September was very wet and many folks are always curious if it was record breaking or not. The answer to this question is perhaps not as straight forward as many would hope it to be. The primary reason is that the vast majority of long term climate data provides 24 hour totals valid at some reporting hour during the daylight hours and not at midnight. This creates an accounting problem for how precipitation is included within a given calendar month since the observation on the first and then the first of the next month can both include partial precipitation totals that are inside and/or outside of the current month of interest. For Iowa and a number of other states, this situation was exasperated by a very heavy rainfall event on the evening of the 30 September into 1 October. In general, this significant rainfall event did not "count" into the September totals as the 24 hour reports came on 1 October. Now for a handful of reporting sites with 24 hours reports near midnight, it did, but for things like climate district and statewide estimated totals, it did not. Oh boy! So the featured chart presents a summary of the impact of this event on September precipitation ranks for the unofficial IEM computed climate district values. The first two data columns are generally the "standard" way with the 24 hour report on 1 October not included. The second set of columns include the 1 October report, but then drop the 1 September report. The final column presents the rank change between the two. Note that the ranks are computed for the exact specified days in each case. The top five largest positive and negative rank changes are shown along with the Iowa values. So two Iowa districts are shown as being second wettest, but wettest if that last big rainfall event was included.

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The featured chart presents the combination of average September high temperature vs low temperature by year for a statewide averaged value for Iowa. The plot is separated into quadrants based on the averages for each. It is certainly most common to have both values either both above or both below average. The 2026 value is highlighted and while having one of the warmest average low temperatures on record, the average high temperature was not that exceptional. Such was the case this past September with ample cloudiness and elevated humidity preventing overnight cooling and thus buoying low temperatures. Much chillier over night temperatures have already occurred this October as clear skies and lower humidity have allowed temperatures to rapidly cool during the overnight hours.

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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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