Thursday saw much needed rainfall over a decent chunk of Iowa. The Ames area received two to over three inches of rain, so it is a good time to check in on the ISU soil moisture sensors to see if the rain soaked in. The featured chart is from the sensor at the "Kitchen Farm", just southwest of Ames. The chart plots the soil moisture sensors at various depths down to 40 inches below the surface since the start of June. The side panels show the depth soil moisture values at the start of June and the most recent observation plotted. The soaking nature of the rain is immediately noticeable with even the shallowest depth starting to dry as the water soaks deeper into the soil. You may be wondering what is happening with the 40 inch value as a 0.7 volumetric value is very high. The belief/hope is that the water table rose to a depth shallower than 40 inches and so the sensor at that depth is submerged. The sensor is in a "prairie pot hole" region with a shallow water table.

Generate This Chart on IEM Website

It has been a somewhat strange year for severe weather to date for the United States. April was very busy for severe weather in and around Iowa, but it continued to be mostly quiet over the southeastern US. May was about the exact opposite of April with much quieter weather, but also for much of the rest of the country as well. The featured chart looks into an aspect of this by totaling up the number of Severe Thunderstorm and Tornado watches issued by the Storm Prediction Center for the year to date period. The top panel shows the total number of watches with the second panel totaling the number of watch outline polygons (note they are no longer the official watch area, but a close approximation) that touched Iowa. The bottom panel plots the percentage touching Iowa. Interestingly, 2026 comes in with the highest percentage since 2004!

Generate This Chart on IEM Website

The featured chart compares yearly precipitation totals between Cedar Rapids and Ames. Blue bars indicate Cedar Rapids was wetter than Ames by the given margin and red bars indicate Ames was wetter. This chart nicely shows the variability that exists on the yearly time scale between two sites that have an overall average difference of just 0.37 inches (~1% of the yearly total). There have been just under 20 years with the difference between the two sites over 10 inches (~30% of the yearly total). The overall frequencies of which site is wetter is not that much different with Ames only have six more such years. This just goes to show how variable precipitation can be over even considerable periods of time.

Generate This Chart on IEM Website

Monday was yet another rather warm day with high temperatures well into the 80s for most of the state. For Des Moines, it was the 19th day so far this year with a high temperature in the 80s. The featured chart presents the climatology, 2025, and 2026 totals for year to date days with a daily high temperature within the given temperature range. The totals within the 70s and 80s are both well above average for 2026, but interestingly about average for the 60s. The forecast for the rest of the week looks to continue totaling up days with highs in the 80s.

Generate This Chart on IEM Website

On average, June is Iowa's wettest month. So it seems appropriate for the start of June to look into precipitation climatology. The featured chart presents the official NCEI daily climatology for Des Moines along with the previous official version. NCEI updates the climatology every ten years to represent a recent 30 year period. A climatology of precipitation is somewhat tricky as the dataset is dominated by dry days (zeros) and heavy rainfall events that skew simple daily statistics. Average daily values become somewhat meaningless, but the annual cycle is still illustrative as shown by the featured chart. It is interesting to see the July dip that shows up in the current (1991-2020) climatology, which is likely due to a number of dry Julys during the 2010s.

Generate This Chart on IEM Website

Our early summer warmth continued on Thursday with highs well into the 80s and even a few 90s across Iowa. For Sioux City, Thursday was the fourth consecutive day with a high temperature of at least 90°F. The featured chart looks into the frequency of a given day of the year participating within such a high temperature streak. The side tables list out the earliest and latest such events on record for the site. This year's event ties for sixth earliest. The high temperature for Friday won't be quite as warm, so the streak will end at four days for the site.

Generate This Chart on IEM Website

Cloud watchers over central Iowa were treated to Lenticular Clouds on Wednesday afternoon. While this type of cloud is often observed on the leeward side of mountains, it takes a special environment to produce them in the absence of significant topography. In this case, a northeasterly propagating gravity wave into flow going in the opposite direction likely combined to produce a "standing wave" environment necessary for these clouds to form. You can find a satellite lapse showing the gravity wave interaction. The clouds have a smooth appearance as the flow sculpts the cloud stuck in the crest of the standing wave. A time lapse from ISU was captured and available on YouTube that shows the stationary nature of the clouds. Again, you'll find plenty of much fancier and more dramatic examples of these clouds near mountains on the Internet, but such displays on the plains are rare! Hope you were able to see them.

USDA NASS published their weekly crop progress update yesterday and estimated 94% of Iowa's corn crop now planted. The featured map presents the statewide estimates with a departures against a simple and linear interpolated ten year average valid 24 May. All of the major corn producing states are shown in good shape. The mostly dry weather this week will likely push Iowa's value to near 100% by next week as the spring planting season draws to a close.

Generate This Chart on IEM Website

For most of the state, rainfall amounts over the Memorial Day weekend were rather meager. Much of the state continues to "run on fumes", so to speak, after the wet April and heavy rains mid May. The featured chart shows the fickle rainfall story for Ames this May with the blue bars showing observed daily rainfall with the red bars indicating the month to date departure from average. The observed and climatological accumulation are plotted as well. Those aforementioned mid May rains are about all there is to speak of for Ames during May. The big rainfall on the 18th put the month-to-date departure barely above average and the departures are again grown since. The bad news is that the next week and perhaps even the next two weeks look very dry with warmer temperatures and reduced humidity, which will quickly escalate the drought situation during what should be the wettest portion of the year.

Generate This Chart on IEM Website

The featured map presents May to date precipitation departures courtesy of PRISM. There is plenty of red (below average departures) to be found on the map. Outside of the rainfall events of last weekend, there has not been much to speak of for rain during May. Much of Iowa is surviving from the very wet April and the periods of reduced water demand like what was found this week with the cool and cloudy conditions. The precipitation forecast for the rest of May is not that bullish and temperatures will be increasing, which will start to materialize impacts over the driest parts of the state this May. For this time of year, it roughly takes about an inch of rain per week just to keep up with climatology, so departures can rapidly build when we get dry periods during the wettest portion of the year!

Generate This Chart on IEM Website

After a very dry start to May, this past weekend saw numerous rounds of severe weather that also brought much needed rainfall. Such is the conundrum this time of year, needed and significant spring season rains often come with thunderstorms that are sometimes severe. The featured chart attempts to look into how much precipitation is associated with severe weather by totaling up one minute interval precipitation totals from the Des Moines airport when either a severe thunderstorm or tornado warning is activate for the airport. The left two panels report the precipitation partitioning percentages during, within an hour, and outside of severe warnings. The upper right panel shows the frequency of a given one minute intensity happening during a severe weather warning. The bottom right panel is a bit of a downer, but denotes how much of the one minute precipitation is likely missing within the one minute observations (long story, but NCEI's collection and distribution of one minute data has become very unreliable). So the overall percentages are not that large with precipitation totals near 10%, but it certainly accounts for a good portion of the most intense rainfall totals.

Generate This Chart on IEM Website

For mid May, Tuesday was a bit chilly with high temperatures struggling to get out of the 50s. Such chilly temperatures imply a meager growing degree day accumulation, which is ever important this time of year to promote crop development. The featured chart presents daily growing degree days for Des Moines with the observed value on Tuesday plotted along with two model forecasts, a crude daily average accumulation (short daily lines) and the associated accumulated values. The NWS NDFD forecast does go out as far as the GFS deterministic model, so that is why the red bars stop on the 26th. The chart nicely shows that we'll have four more days to go with below average GDDs prior to about a week of warmer weather taking us into June.

Generate This Chart on IEM Website

Storms developed along a frontal boundary over southwestern Iowa on Monday afternoon with muggy air ahead of the front helping to fuel the storms. Cooler and less humid air has worked into the state overnight with dew point temperatures 10 to 15 degrees cooler. The featured chart looks into six hour dew point temperature change based on hourly data from the Des Moines airport. The data is partitioned by one degree Fahrenheit and by week of the year with the frequency units being average number of hours per week per year. Certainly values near zero are the most common as dew point fluctuations are less than air temperature. It is interesting to denote the largest frequencies at values just above zero during late June into late August. Some of this is the effect of evapo-transpiration processes adding moisture to the air during daytime hours, but it is also a tightening of the possible distribution of dew point temperatures during the most humid time of the year.

Generate This Chart on IEM Website

The featured chart presents a time series of hourly dew point temperatures for Ames since 25 April. The lack of humidity during the month of May has dramatically reversed over this past weekend with even a 70°F dew point observation on Sunday. The return of humidity has certainly helped the return of spring time thunderstorms and severe weather with more of both expected on Monday.

Generate This Chart on IEM Website

After a very wet April, May has been the exact opposite with very little rainfall to speak of. An unofficial IEM Iowa statewide estimate indicates the first 14 days of May being the driest on record since at least 1893. Thankfully, this situation is about to change and the subject of today's featured map. The map depicts Weather Prediction Center's seven day precipitation forecast along with the latest US Drought Monitor released on Thursday. The entire state is shown in the 1.5 to near three inch range.

Generate This Chart on IEM Website

For Iowa State students, this is Finals week. For K-12 students, just a few weeks of school remain until summer break. So it is a good time to think about summer and present a metric to compute when the summer season begins. If you consider the summer season as the warmest consecutive 91 day period (1/4th of the year) each year, the featured chart plots the start date each year for this period for Ames. The dots are colored by the average temperature departure for this period over all years. A simple linear trend line is plotted as well. The overall average is around 7 June, which just over three weeks away, but plenty of years got started in just over week from now.

Generate This Chart on IEM Website

Our mostly dry and lack of humidity start to May continued on Tuesday with dew point temperatures in the 30s and lower 40s. The featured chart presents a climatology of daily maximum dew point as calculated by available hourly observations from the Des Moines airport. The 2026 observations are shown as blue dots on the top panel. Each of the daily dots for May is found below a simple long term average for the day. This is in stark contrast to the elevated humidity levels that were common for much of April.

Generate This Chart on IEM Website

It has been a rather strange start to the growing season. The month of April was quite warm and wet, leading to an early start to the growing season with plenty of growing degree days accumulated prior to the start of May. May has now started off rather dry with low humidity levels allowing overnight temperatures to cool below freezing over a number of days so far this May. USDA NASS released their weekly crop progress report yesterday and estimated 72% of Iowa's corn crop having already been planted, a 30 percentage point increase over the estimate last week thanks to the mostly dry start to May. The featured chart looks into the weekly percentage point change in crop planting progress as estimated by NASS. The left hand labels show the year and the maximum weekly change value for each year. A 30 percentage point change is about at the middle of possible yearly maximum values.

Generate This Chart on IEM Website

It is difficult to imagine the weather on Mothers Day being any better with ample sunshine, a cool breeze, low humidity, and high temperatures around 70°F. The featured chart presents the yearly Mothers Day high temperature as recorded at Des Moines. The previous two years had quite warm temperatures with highs above 80°F, but this year's high of 72°F was just a degree or so above a simple long term average value. While most mothers probably would have preferred it not to rain yesterday, much of the state is starting to need rain again as the growing season is now fully underway and it has been about two weeks since Iowa's most recent widespread and significant rainfall. The near term forecast is not very optimistic about upcoming rainfall events.

Generate This Chart on IEM Website

Temperatures were rather pleasant on Thursday with mid 60s common over much of Iowa during the afternoon hours. Ames reported a temperature of 66°F at 3 PM. The featured chart looks into the frequency of having such a temperature by month for Ames. The bars present the frequency of having a temperature within the inclusive range of 63 to 67°F at 2 PM LST (3 PM CDT) with the blue dots showing the frequency below that range and red dots above. May does have the highest frequency of such temperatures, but only by a slim margin to April. It is kind of interesting to denote the near identical frequencies between February and July!

Generate This Chart on IEM Website