The parade of thunderstorm complexes looks to continue on Friday and into the weekend. On Thursday, the Weather Prediction Center (WPC) issued a rare, for Iowa, Day 2 "moderate risk" of excessive rainfall for Friday into Saturday morning. The featured map presents the number of such issued risks since the start of the available archive during late 2015. Most of Iowa is shown having less than five such events over this period. Today's moderate risk was issued for southeastern Iowa, which has only slightly few more events on record. The IEM attempts to curate a downloadable archive of these outlooks and also has a simple search tool to find outlook events by a point location.

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This week has featured a parade of early morning thunderstorm complexes. The one on Tuesday morning has been preliminary classified as a "derecho" by the Storm Prediction Center. The featured movie combines a NWS RADAR mosaic with Severe Thunderstorm and Tornado warnings along with NWS Local Storm Reports. The bottom panel plots the report times of the severe wind gusts between 7 AM and 12:30 PM on 11 August 2026. Of course, it is unnerving to have such events occur so close to the anniversary of the 10 August 2020 derecho. The Tuesday event also produced a few tornadoes in Iowa and near Chicago. The Storm Prediction Center has a webpage with more information about derechos.

For the National Weather Service office at Davenport (Quad Cities), it has been a very active year for severe weather. Severe storms once again visited eastern Iowa early Tuesday morning with three EF-1 tornadoes surveyed over Delaware County. Based on unofficial IEM archives, the featured chart presents the number of year to date Tornado Warnings issued by the office since 1986. The 2026 total of 86 warnings easily surpasses any previous year. Unfortunately, more chances of severe weather are in the forecast for much of the remainder of this week.

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Atmospheric soundings are an important observational dataset useful for the forecasting the weather. The often twice-daily balloon launches by the National Weather Service capture vertical profiles of temperature, humidity, pressure, and wind. These profiles can be used to compute many useful indices to access the state of the troposphere. Once such index is Convective Available Potential Energy (CAPE), which is useful for understanding how much potential energy is available for near surface air if it were to be lifted vertically and become buoyant. The CAPE index is not necessarily easy to compute and subject to many interpretations and assumptions. The featured chart presents the CAPE index for surface based "parcels" based on soundings from NWS Davenport. The balloon launch Monday evening (00 UTC 11 August 2026) captured a very unstable environment with a CAPE index around 7,700 J/kg. Based on unofficial archives, this was the largest CAPE value for August and one of the largest on record for the site. Large CAPE values are often associated with a "cap" of warm air aloft that prevents storm development, so these environments do not automatically produce severe storms. Generally speaking, CAPE is not a lifting mechanism but an energy reservoir available to support explosive development should air be lifted to levels were it can "freely convect".

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Severe storms impacted eastern Iowa Friday afternoon producing an EF2 Tornado near Fairbank and damaging winds elsewhere. When the National Weather Services issues Severe Thunderstorm and Tornado Warnings for such storms, the warnings contain an estimate of storm speed and direction of travel. The featured chart presents such storm motion estimates from NWS Davenport during the summer months of June, July, and August (JJA). The warnings from Friday are highlighted with the red crosses. The blue lines attempt to show where the most frequent combinations of storm speed and motion reside. The bullseye appears to be somewhere near a storm motion from the west around 40 MPH. You can generate this chart for other months of the year and compare how the storm motion changes during the year.

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One of the most frequently issued National Weather Service headlines is the ever exciting Dense Fog Advisory. A number of such advisories have been issued over Iowa this week as a cooler air mass has interacted with late summer elevated humidity. The featured chart looks into the frequency of such advisories issued by NWS Des Moines by time of day. The chart presents the summer season (June, July, August) frequency along with the overall full year frequency. The difference between the two is quite informative. During the summer season, solar inputs are very strong and will work to "burn off" the fog pretty much every day. Of course, there is no "burning" process, but a process of heating the ground, heating the lower atmosphere and reducing relative humidity levels. Such is the case again this Friday with morning fog and a number of advisories currently active.

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For the first week of August, Wednesday was a very cool day with a number of locations unable to reach a high temperature of 70°F. One such location was Waterloo with a high of just 69°F. The featured chart looks into the accumulated frequency by fall season date for the first sub threshold daily high temperature. The algorithm considers any post 1 July date as the "fall season", but starts the plot on 1 August. For the sub 70°F threshold, yesterday's value comes in around the 10th percentile. Rewording, about one in ten years have seen such a cool high by the 5th of August. Some selected lower thresholds are plotted as well with sub 65°F having a much lower accumulated frequency until about the last week of August. We are still squarely within the summer season for Iowa, so these respites from the heat should be enjoyed!

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In the category of life imitating art, yesterday (4 August 2026) was the future date referenced in the 1950 short story "There Will Come Soft Rains" written by Ray Bradbury. While some Iowans did experience something more than soft rains, a majority of the state received something much softer. The featured chart presents one minute interval data from the ISU Soil Moisture station just west of Ames. The bottom panel shows the one minute interval rainfall totals. The station utilizes a classic tipping bucket to report rainfall in 0.01 inch increments (one tip of the automated mechanism). So the minute totals are not a true minute accumulation as the time to generate one tip can take more than one minute. The label above the plot provides the maximum rainfall accumulations over various intervals of time. Those maximum values are not excessive at all and likely quality as a "soft rain" for most folks!

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Agronomy Hall at Iowa State University hosts a PurpleAir air quality sensor. Unfortunately, wild fires and the associated smoke continues to be a problem plaguing much of the country. The featured chart presents the daily range of PM2.5 (2.5 micrometers or less) Air Quality Index (AQI) for 2026. The chart colors represent the ranges of values associated with the given AQI rating. The wild fire smoke has certainly been noticeable over Iowa these past number of weeks. The hazardous levels were reached just over a week ago on 24 July.

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With the calendar now turned into August, we have fully reached the last half of the warmest part of the year. Average high temperatures have been slightly above average for the June through July period. The featured chart looks into if this portends what may happen during the August through September period. The chart presents the yearly combination of average high temperature for Ames for the sixty days prior to and after 1 August. Of note for this plot are the quadrant frequencies, which indicate a persistence to having both periods either below average or above average each year.

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Today's feature continues the recent series looking into the record setting dew point temperatures from earlier this week. Dew point extremes are not an official climate metric tracked by the National Weather Service, so entities like the IEM create period of record statistics based on hourly observations. So while there is no official Iowa dew point temperature record, discussions with various Iowa climate experts have often concluded that 87°F on 13 Jul 1995 for Cedar Rapids is it. Three airport weather stations reported maximum dew point temperatures above 87°F earlier this week, but yesterday's IEM feature attempted to explain those away as just bad data / poor sensor performance. Today's featured chart takes another look into one of the problematic maximum dew point readings (Algona). It is compared with a nearby ISU Soil Moisture station (Kanawha) and the Ames airport station over Sunday and Monday. Ames reported a maximum of 86°F, so it is good to inspect the three time-series to see if the patterns make sense. Two areas are shaded each day as informative times to observe temperature and dew point changes. The light red area (7 AM - noon) represents a period of increasing net radiation and vertical air mixing. The light blue area (6-8 PM) often represents a period of stabilization as air temperatures start to decrease but evapo-transpiration may still be on-going. The top two subplots present coherent depictions of increasing day time temperatures allowing for a vapor pressure deficit that can support evapo-transpiration increasing the dew point. For the second day, a drier air mass was working its way into Iowa during the afternoon hours and you can see rather poor sensor performance at the Algona site vs nearby Kanawha. The Ames 86°F reading appears to be associated with the aforementioned early evening brief period with on-going transpiration and reduced vertical mixing. The "Generate This Chart" button takes you to the ASOS one minute plotting tool for Ames, which provides some more clues to what drove the 86°F dew point.

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It is a tale as old as time, it seems. For the most humid days of the summer, a couple of the non-federal airport weather sensors in Iowa will report incredible dew point readings, often reaching the low 90s°F. "Corn sweat" is immediately attributed to these without much considering if such readings are even physically possible. The next level of attribution claims that these sensors are located within corn fields, so they are sensing the corn field environment and since Iowa is mostly covered by corn and soybean fields, that this reading, while high, is still representative of the state. So like what the IEM did back in August 2023, today's feature attempts to simply explain those high readings as bad data / poor sensor performance. There are three main airport weather station network types with Iowa. The "Federal ASOS" sites maintained by the FAA/NWS. The "Federal AWOS" sites maintained by the FAA. The "Non-Federal AWOS" sites that are operated by the Iowa DOT. These sites have different sensor packages, siting requirements, and maintenance methods. While a number of ASOS sites set dew point records earlier this week, a few AWOS sites reported even higher dew point temperatures in the upper 80s and even low 90s. The featured chart presents some humidity metrics over the past most humid days with the colors representing the network type that the airport weather station belongs to. Some logical and charted points to why such high dew points are bad.

1. The 90°F dew point club (Clarion, Algona) are clearly having a problem with reporting too high of relative humidity (RH) and often "stuck" at 100% (first column). They are also reporting way too high RH during the afternoon hours (last column) vs all other sites over Iowa.
2. The high RH frequencies, if accurate, would also imply reduced crop transpiration as saturated air can not take on more water vapor. This creates a conundrum for the theory that "corn sweat" can drive such high dew points when the sensor indicates high RH already.
3. Ultimately, the very high dew points are just a sign of the sensor struggling to accurately measure humidity under extreme humidity levels. There is likely some water condensation within the sensor causing it to over-report humidity.

Recapping, "corn sweat" certainly drives higher dew point temperatures in Iowa and the effect is nicely documented with this Wolf and Market article. The effect can only push dew point temperatures so far into the lower 80s.

While still quite humid, Tuesday felt much better than the oppressive humidity of the previous two days. Humidity levels, as measured by dew point temperature, were at or close to period of record maximum values for a number of airport stations over Iowa and beyond. It stands to reason that the heat index was at near record values as well. The featured chart presents the top 10 dates for maximum heat index for Des Moines. Only the highest value each day is plotted once, so this list isn't the top ten hourly heat index values, but top ten dates for highest heat index value. Anyway, Sunday and Monday are both shown on this list with Monday's 119.7°F (Temp: 94°F, Dew Point: 83°F) coming in second place. As an aside, the National Weather Service continues to work toward replacing heat index usage with an index called Wet Bulb Globe Temperature (WBGT), which takes more weather variables into account. The replacement is still more than a year or more away.

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Held during the last full week of July, RAGBRAI is a seven day bike ride from west to east across Iowa. This year's event finished up this past weekend with most days being rather pleasant for biking and overnight camping. The featured chart presents two weather metrics during each year's ride using the Des Moines airport data as a representative proxy for statewide conditions. Of course a more rigorous weather analysis could be done using more route specific airport station data, but the chart hopefully is a close approximation. The top panel shows the number of hours each year with a heat index of at least 85°F. The bottom panel analyzes wind speed and direction, producing an averaged vector component wind in the east/west direction. For the bottom chart, red values would indicate a net average head wind. So the top panel shows the reduced number of hours with 85+°F heat index vs a long term simple average and even the past three years. The bottom panel as well shows a reduced head winds vs the previous three years.

Sunday was incredibly hot and humid over Iowa with afternoon dew point temperatures in the low 80s and air temperatures in the 90s! The featured info-graphic presents IEM computed maximum dew point temperatures on Sunday along with period of record maximums based on unofficial IEM archives of NOAA/NWS data. There are many caveats to this type of analyses as true daily maximum dew point temperatures are not something officially reported nor curated by the NWS. The long term archive is based on mostly hourly reports. Additionally, stations have changed instrumentation, observation techniques, and local surrounding vegetation over the years. All of these items make period of record comparisons problematic. This graphic also is limited to the long term airport sites that are federally maintained. You may have seen other reports about Iowa denoting dew point readings reaching 90°F at state maintained airport stations on Sunday. These values are very likely in error. So having said all of that, three of the listed sites (Ames, Burlington, and Ottumwa) hit period of records on Sunday. Monday will be another very hot and humid day, but hopefully a few degrees less humid than Sunday!

Updated: A news item has been posted containing a more complete accounting of the record dewpoints over 25-27 July 2026.

With a low temperature of 52°F on Thursday, Dubuque tied the daily record for 23 July. The featured chart presents the daily high and low temperature climatology for Dubuque along with the 2026 observations. Any set or tied records are denoted with the small dot. What's interesting about Thursday's record is that the value is also the warmest minimum low temperature record for the site. So perhaps you may consider it as the easiest low temperature record to tie during the month of July. That aside, our very enjoyable respite from typical Iowa summer weather ends on Saturday, so hopefully you can enjoy the nice temperatures today!

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For mid July, the weather does not get much nicer than what Iowans experienced on Wednesday with high temperatures in the 70s and dew points mostly in the 50s. Based on hourly reports, the maximum dew point for Des Moines was just 59°F. The featured chart looks into the frequency of having a sub 60°F maximum daily dew point. The top panel presents the daily maximum dew point climatology along with the 2025 and 2026 observations. The 59°F value yesterday is highlighted by the red box and you have to back to late June to find as low of a value. The bottom panel directly addresses the frequency question of today's feature and shows the mid July value near 5%. The nice weather was very welcome for all of the bike riders currently on RAGBRAI!

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The featured map presents an accumulated precipitation estimate for July 2026 to date courtesy of NOAA MRMS. A sizable chunk of Iowa is indicated receiving less than two inches so far with another sizable chunk in the six to ten inches and even higher range. An average accumulation for the first third of July is around three inches, so it has been a dry month for some in the state! The heavy precipitation events have been isolated, which is typical this time of year due to reduced storm motions and increased precipitation rates due to elevated atmospheric humidity levels. These precipitation contrasts over short distances can have significant implications for water availability and stress for agricultural crops.

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The area between Ames and Des Moines has had quite the July for heavy rainfall events. After an event on 2-3 July brought upwards of ten inches just northeast of Des Moines, another deluge of rain fell Monday evening (20 July) with roughly the same area targeted with the highest amounts. The featured map presents the combination of MRMS 24 hour precipitation estimates ending Tuesday morning with available NWS Local Storm Reports, COOP observations, and CoCoRaHS reports. The map will be updated later on Tuesday after more morning reports are received. While totals with this event were much lower than the one earlier this month, values over four inches are still rather exceptional and even more exceptional to have two such events over the same location during one year.

Up until Sunday, Iowa had mostly avoided the smoke plumes originating from the wild fires over northern Minnesota and Ontario, Canada. Unfortunately, the smoke arrived over eastern Iowa on Sunday. The featured map presents an accounting of the number of hours since 6 July that a plotted airport weather station has reported smoke within its METAR observation report. Smoke is encoded as "FU" within a METAR and that code originates from the French word Fumée, for those of you that are curious. The map shows the largest total number of hours stretching from northern Michigan to the east coast.