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.
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!
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.
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.
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!
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.
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.
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.
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!
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.
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.
Strong northwesterly winds are ushering in the coldest air of the season so far with sub-freezing temperatures expected over much of the state Friday night into Saturday morning. Such winds have been noticeably missing this fall season and one of the reasons why temperatures have been so warm for the season to date period. The featured image takes a look into that by plotting wind roses for the 1 September through 14 October period for 2026 (left plot) and the period of record (right plot) over the same period each year. A wind rose is a histogram of wind speed and direction plotted in a polar coordinate. This plot uses a meteorology convention with the bar direction indicating the direction from which the wind is blowing from. A visual comparison between the two plots is very telling with an immediate lack of westerly through northerly winds throughout the 2026 period. Wind from this direction is typically bringing in cooler air, which has been lacking this season. Instead, plenty of southeasterly flow is shown which is typically warmer and more humid.
Sub-freezing temperatures finally visited Iowa Saturday morning. It was one of the latest first freeze dates for any location in the state on record. Rewording, since at least 1893 and prior to 2026, at least one long term climate site has seen a sub-freezing temperature by 16 October. The featured map presents an analysis of 15 minute interval Real-Time Mesoscale Analysis (RTMA) minimum temperature during Saturday morning. Only some parts of southern Iowa appeared to miss out, but temperatures were not necessarily cold enough for a wide spread "killing freeze". Temperatures were warmer on Sunday and a warming trend is expected for this week, so a return of freezing temperatures is not expected until at least next week.
It is difficult to imagine more perfect fall weather than what we had on Monday with most locations having highs in the 60s, lows in the 40s and not much for wind. The featured chart looks into the daily frequency of having a high in the 60s, a low below 50°F, and a max sustained wind speed below 20 MPH for Des Moines. This type of weather is clearly isolated to the spring and fall seasons with combined frequency peaks, shown by the black line, occurring during each season. The month of October has the highest frequency at around 17%, so this is the time of year for such wonderful weather!
USDA NASS released their weekly crop progress update on Monday and Iowa, among other Midwestern states, remains a bit behind on soybean harvest progress as of this past Sunday. The featured map presents the most recent NASS estimated percentage of acres harvested along with a percentage points difference from a ten year average approximately valid for 18 October. Better weather this October vs September has certainly helped progress to be made, but many fields remain quite wet and much more drier weather is needed. You can generate this same map for corn and find a similar story for Iowa. Soybeans tend to be harvested first in Iowa as the crop matures sooner and farmers have a desire to get it out of the field before colder November weather brings chances of snow!
The Hazardous Weather Outlook (HWO) is a text product narrative issued by National Weather Service Weather Forecast Offices (WFO) highlighting hazardous weather threats over the coming few days. This product has been deprecated by many WFOs as no longer being useful / containing redundant information found in other products. The product does live on though for some WFOs with the featured map displaying the number of HWOs issued so far this month by WFO. For the Iowa WFOs, NWS Des Moines stopped HWOs at the end of September and NWS Omaha stopped back in June. For those curious, the oldest HWO found in the IEM archive dates back to 1994 and was issued by NWS Hastings, NE.
A week of wonderful fall weather looks to last into the weekend prior to cooler temperatures along with rain chances to start off next week. There have been plenty of daily high temperatures into the upper 70s this week and one may wonder how much longer into the fall season can such temperatures last? The featured chart attempts to answer that question by plotting the latest calendar date a given high temperature was observed at or above a given threshold. The first item to notice is how anomalous the 15 December 2021 event was with a high temperature of 74°F that day! Values in the mid to upper 70s are possible for a few weeks yet, so there is still time for such warmth to occur!
