Past Features

This page lists out the IEM Daily Features for a month at a time. Features have been posted on most days since February 2002. List all feature titles.

Features for Jul 2024

Mon Jul 01, 2024
June Flight Rules
01 Jul 2024 05:30 AM
The primary purpose of an airport weather station is support aviation needs for planes to take off and land. The combination of horizontal visibility and height to cloud ceiling establishes a flight rule category, which may limit the types of aircraft and pilots that can fly during that time. The featured chart presents the hourly flight rule category for Des Moines for the month of June. Visual Flight Rules (VFR) dominated for the month, which is typical as cloud decks are typically quite high and fog conditions are limited. This type of chart nicely summarizes when the worst of the month's conditions occurred, which was clearly on the 19th and 20th of the month.
Voting: Good - 10 Bad - 0

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Tue Jul 02, 2024
Warmest Fiscal Year
02 Jul 2024 05:30 AM
For some entities, 1 July started a new fiscal year. So it seems appropriate to average up temperatures over this recently ended year and see how 2023-2024 compares. For Waterloo, the most recently ended stretch between 1 July and 30 June was the warmest on record! For most sites over north-central Iowa, this past year was at least top five and often at least second warmest behind 2011-2012. The warm winter season and recent El Nino both contributed toward the record warmth. July has actually gotten off to a rather chilly start with highs not even reaching 70 degrees for some parts of the state for the first day of the month. Of course, the fiscal year widely varies by entity, so you are certainly welcome to generate this chart for your desired 365 day period of choice!
Voting: Good - 11 Bad - 1

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Wed Jul 03, 2024
2024 Precipitable Water
03 Jul 2024 05:30 AM
More rounds of heavy precipitation visited Iowa on Tuesday thanks to a very warm atmosphere loaded with water vapor. Such air masses are able to support efficient rainfall makers and significant amounts of total rainfall. A measure of how much water vapor is present in the troposphere is expressed by a term called precipitable water. This depth represents the amount of liquid water present in a column of air if all the water vapor is condensed. The featured chart presents a time series of this metric for Davenport along with a period of record climatology. Interestingly, the past few days have seen a remarkable swing from a very dry atmosphere at near the bottom of the climatological range to one closer to the top. July and August are the time of year for such water rich air masses as the amount of water vapor air can hold is a function of its temperature, so the warmer temperatures get, the more water vapor it can hold!
Voting: Good - 9 Bad - 0

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Thu Jul 04, 2024
Three Hour FFG
04 Jul 2024 05:30 AM
Flash Flood Guidance (FFG) is a product issued by NWS River Forecast Centers (RFC)s to estimate the amount of rainfall over a given interval of time to cause small stream and urban flooding. The product is very much linked to the capacity of top soil to infiltrate rain water at a given rate. Recent heavy rainfall events have near surface soils quite saturated and the featured map showing a recent three hour duration FFG for Iowa indicates where some of those areas are, by how low the values are. Some parts of the state are shown below two inches, which is very low for this time of year with efficient and slow moving thunderstorms easily able to produce such rates. So look for more Flash Flood warnings with upcoming heavy rainfall events as it will not take much.
Voting: Good - 6 Bad - 0

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Fri Jul 05, 2024
Nature's Fireworks
05 Jul 2024 05:41 AM
While a line of storms did form Thursday evening, the overall state coverage was isolated and so much of the state had an excellent evening to enjoy fireworks. Nature's fireworks, in the form of lightning, is the subject of today's featured map. It presents a stroke frequency analyses courtesy of the National Lightning Detection Network for Thursday. Most of the lightning yesterday was confined to northern Iowa. There was some worry within the weather forecast for yesterday that much of the evening would be a washout for much of the state, but thankfully that did not happen.
Voting: Good - 10 Bad - 1

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Mon Jul 08, 2024
Brief and Intense Rainfall
08 Jul 2024 05:30 AM
A brief and very intense rainfall event was captured by the Mason City airport weather station on July 4th. The featured chart presents one minute interval precipitation reports between 4:45 and 5:30 PM. Over just 10 minutes between 5 and 5:10 PM, 1.16" of precipitation was reported! This is about as extreme of a rate that has been observed over Iowa. Thankfully, this rate was not sustained over an hour for a single location as it would equate to over 6.5"! Additionally, you can see an instantaneous rate of over 10 inches per hour was found with the one minute data. This is the time of year for such high precipitation rates as a warmer troposphere can hold more water vapor and less cloud ice induction increases precipitation efficiency. Storms also move less quickly, which helps to isolate precipitation totals further.
Voting: Good - 17 Bad - 0

Tags:   heavyrain  
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Tue Jul 09, 2024
Beryl Tornado Warnings
09 Jul 2024 05:30 AM
While over the ocean, Hurricane Beryl was a historic tropical system for a number of reasons including reaching category 5 status so early in the season, its longevity, the region it developed in, and regaining Hurricane status after a significant incursion of dry air and hostile shear environment. So it makes sense that it continued to make history after landfall on Texas early Monday morning. The storm did significant damage along the gulf coast from the traditional threats of rainfall, storm surge, and wind. It then transitioned into a prodigious tornado producer as the right front quadrant of the storm was in an abnormally primed environment to produce tornadoes. The NWS followed suit and issued a large number of tornado warnings for the date. It is difficult to state how anomalous this event was given that it happened during the first half of July. The featured chart presents an IEM accounting of the largest number of tornado warnings issued by the NWS for a July date. NWS Shreveport issued 67 warnings itself yesterday, which matches the previous NWS-wide max total for a US Central calendar day in July! Yesterday also made for the 6th day this year with over 100 tornado warnings, which places 2024 in second place for such a metric behind nine days during 2011.
Voting: Good - 14 Bad - 1

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Wed Jul 10, 2024
Pleasant July Dew Points
10 Jul 2024 05:30 AM
For July, the combination of air temperature and dew point readings on Tuesday made for a pleasant day. The featured plot attempts to put the dew point values into a bit of climatological context for July for Des Moines. At each air temperature, a dew point climatology is constructed with the purple area representing the 25th to 75th percentile, the green area between the 5th and 95th and the blue line is a simple average. The black dots are the observations from Tuesday. The black line computes the relative humidity value for the combination of air temperature and average dew point. For yesterday, you can see that the values were generally below average for the given temperature. The chart nicely shows the decrease in dew point as temperatures start to exceed the mid 90s. Typically, such temperatures are driven by drier air masses originating from areas outside of the Gulf of Mexico and even drying due to down-sloping from the Rocky Mountains. Additionally, drier air masses are required to partition more of the solar energy into heating the ground than water vapor in the air so to drive higher temperatures. The warmest of air masses are also likely well mixed, so near surface humidity is mixed vertically with drier layers of air.
Voting: Good - 9 Bad - 0

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Thu Jul 11, 2024
Comparing July Lows
11 Jul 2024 05:30 AM
The featured plot is an attempt to illustrate the difference between July low temperatures during a thirty year period that includes the 1930s ("Dust Bowl") and the most recent thirty year period. The top panel presents the data as a kernel density estimate, which attempts to provide a smoothed histogram. The bottom panel differences the two plots. While the y-axis values are a bit obtuse, a larger value indicates a higher frequency. So the difference in distributions between these two periods is more readily apparent. This plot is for Des Moines, so its urban heat island effect is likely somewhat to blame for the increased temperature, but increased humidity levels are also likely to support the increase in frequency for values in the upper 60s and lower 70s. This autoplot can be run for other locations in the country and arbitrary periods of your choice, what changes can you discover?
Voting: Good - 7 Bad - 0

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Fri Jul 12, 2024
Warmest Day of July
12 Jul 2024 05:30 AM
One of the reasons why the drought of 2023 was not more damaging to crops was that July 2023 was not all that hot, which reduced water stress. Interestingly, July 2024 has again not been all that hot and while drought is presently not a concern, the lack of excessive heat is again very positive to crops. The forecast does have a few hot days coming up, but then a cool down expected by mid week. The featured chart looks into which days of the month have the warmest high or low temperature for Ames. There really isn't a preferred time of the month as July contains the climatological warmest average temperatures of the year within the middle of the month, so there is no directional preference from the start of the month to the end.
Voting: Good - 12 Bad - 0

Tags:   jul  
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Mon Jul 15, 2024
Daily Max Feels Like
15 Jul 2024 05:30 AM
It certainly felt like summer in Iowa over the weekend with heat index values reaching the triple digits for much of the state. The featured chart is an attempt at computing a climatology for daily maximum feels like temperature (combination of wind chill and heat index). An immediate caveat is that during the cold season, this metric isn't all that intuitive as it represents the warmest daily wind chill and not the coldest. That aside, the plot is based on period of record hourly or better observations from Des Moines with the present day heat index and wind chill equations applied to the archive. The top panel shows a smoothed presentation of the climatology with the blue dots representing the 2024 observations. Since the climatology is smoothed over seven days, the observations can sometimes appear outside of the bounds. The bottom panel shows the daily frequency of having a maximum heat index of at least 100 degrees. The middle of July is certainly the peak time of year for such hot conditions. We'll have another such day on Monday before cooler weather arrives for the rest of the week.
Voting: Good - 13 Bad - 0

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Tue Jul 16, 2024
July 15 Possible Derecho
16 Jul 2024 05:23 AM
The severe weather threat on Monday materialized as forecast with a cluster of strong storms developing mid afternoon over central Iowa and then congealed into a damaging line of storms that plowed east. At the time of this feature writing, this system has yet to be a labelled a derecho, but it seems likely that it met the criteria of duration and areal coverage. The featured map presents NWS Local Storm Reports of thunderstorm wind gust and damage. As with many storms this year, this system appeared to produce a number of brief tornadoes as well making the event even more dangerous. NWS offices will be out surveying the damage today and the IEM has a Google Group you can subscribe to for email alerts when they issue damage survey reports.
Voting: Good - 18 Bad - 0

Tags:   derecho  
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Wed Jul 17, 2024

July 15 Derecho
17 Jul 2024 05:30 AM
The storm complex from Monday afternoon into evening has been classified as a derecho by the Storm Prediction Center. The featured lapse combines NWS RADAR, Warnings, and Local Storm Reports between 3 PM and 1 AM Tuesday. The bottom panel attempts to illustrate the persistence of significant wind gust reports with each report having a five minute plot width. You can see that the line was producing consistent wind gusts reports for much of the evening hours. Additionally, EF1 rated tornadoes were confirmed within the Des Moines Metro and Davenport as well.
Voting: Good - 12 Bad - 0

Tags:   derecho  

Features for Jul 2024