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.
Tue Oct 01, 2024
Calm September
01 Oct 2024 05:30 AM
After a number of days this September with not much wind, the increase in wind with the passage of a dry front on Monday was noticeable. The featured chart illustrates how calm this September has been by showing average wind speeds each September for Des Moines. The 2024 value is one of the slowest on record for the site. The lack of passing storm systems certainly contributed to the lack wind for the month. The black line on the upper chart represents a trailing 30 year average and the recent trend certainly seems to be downward. The caveat is that long term wind trend assessment is fraught with peril as observation techniques and instrumentation has changed over the years.
Voting: Good - 10 Bad - 0
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01 Oct 2024 05:30 AM
After a number of days this September with not much wind, the increase in wind with the passage of a dry front on Monday was noticeable. The featured chart illustrates how calm this September has been by showing average wind speeds each September for Des Moines. The 2024 value is one of the slowest on record for the site. The lack of passing storm systems certainly contributed to the lack wind for the month. The black line on the upper chart represents a trailing 30 year average and the recent trend certainly seems to be downward. The caveat is that long term wind trend assessment is fraught with peril as observation techniques and instrumentation has changed over the years.
Voting: Good - 10 Bad - 0
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Wed Oct 02, 2024
September into October
02 Oct 2024 05:30 AM
September was very dry for Iowa, perhaps the driest on record since at least 1893. One may wonder if this will continue into October. The featured chart compares the Iowa statewide precipitation for the past 15 days of September vs about the first 15 days of October. Quadrant frequencies are computed by dividing up the observations by their respective simple averages. The below average for both periods has the highest frequency by a good margin, so having October start off dry as well would be more likely than not. The actual near term forecast is bone dry with some dangerous fire weather conditions upcoming this week.
Voting: Good - 8 Bad - 1
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02 Oct 2024 05:30 AM
September was very dry for Iowa, perhaps the driest on record since at least 1893. One may wonder if this will continue into October. The featured chart compares the Iowa statewide precipitation for the past 15 days of September vs about the first 15 days of October. Quadrant frequencies are computed by dividing up the observations by their respective simple averages. The below average for both periods has the highest frequency by a good margin, so having October start off dry as well would be more likely than not. The actual near term forecast is bone dry with some dangerous fire weather conditions upcoming this week.
Voting: Good - 8 Bad - 1
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Thu Oct 03, 2024
Red Flag Warning Weather
03 Oct 2024 05:30 AM
A Red Flag (Fire Weather) Warning was in effect Wednesday afternoon for much of northwestern Iowa. The NWS issues this headline when antecedent dryness is combined with dry vegetation and the atmospheric combination of low relative humidities and strong winds. As you can imagine, such a combination leads to ignited fires that can spread quickly. The featured chart presents a time series of relative humidity and wind speed reports for Spencer, IA on Wednesday. The duration of the Red Flag Warning is highlighted within the chart. You can see the warning covering the period of lowest relative humidity and strongest winds. By early evening, both conditions had relaxed and the warning was expired. More of the same will be possible for the remainder of this week.
Voting: Good - 15 Bad - 0
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03 Oct 2024 05:30 AM
A Red Flag (Fire Weather) Warning was in effect Wednesday afternoon for much of northwestern Iowa. The NWS issues this headline when antecedent dryness is combined with dry vegetation and the atmospheric combination of low relative humidities and strong winds. As you can imagine, such a combination leads to ignited fires that can spread quickly. The featured chart presents a time series of relative humidity and wind speed reports for Spencer, IA on Wednesday. The duration of the Red Flag Warning is highlighted within the chart. You can see the warning covering the period of lowest relative humidity and strongest winds. By early evening, both conditions had relaxed and the warning was expired. More of the same will be possible for the remainder of this week.
Voting: Good - 15 Bad - 0
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Fri Oct 04, 2024
90+ Degree Days
04 Oct 2024 05:30 AM
The current forecast has parts of Iowa taking a run at 90° high temperatures this weekend, so it is a good time to check in on the accumulated number of such days each year. The featured chart presents the number of days with a high temperature of at least 90°F for Ames. Each year's bar is colored by either being above or below the simple long term average number of days. The yellow line presents a trailing 30 year average. The long term trend has been downward, but that is largely explained by land use changes modifying the surface energy budget and summer time increases in humidity. It is interesting to see the recent and modest increase in number of days over the past five years or so and if that trend will continue over the coming decade or so.
Voting: Good - 17 Bad - 1
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04 Oct 2024 05:30 AM
The current forecast has parts of Iowa taking a run at 90° high temperatures this weekend, so it is a good time to check in on the accumulated number of such days each year. The featured chart presents the number of days with a high temperature of at least 90°F for Ames. Each year's bar is colored by either being above or below the simple long term average number of days. The yellow line presents a trailing 30 year average. The long term trend has been downward, but that is largely explained by land use changes modifying the surface energy budget and summer time increases in humidity. It is interesting to see the recent and modest increase in number of days over the past five years or so and if that trend will continue over the coming decade or so.
Voting: Good - 17 Bad - 1
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Mon Oct 07, 2024
Limited Freeze
07 Oct 2024 08:55 AM
The coolest air of the season to date settled into Iowa overnight with some limited areas of the state likely to have experienced their first freeze. The featured map presents a minimum temperature analysis of the 15 minute interval NWS/NCEP RTMA temperature product. Note that this product is not a true minimum value, but we assume that the 15 minute interval resolution was close enough to capture the minimum. The color ramp and legend intends to highlight temperatures near freezing. The coldest temperatures found within this analysis are over the valley regions of western Iowa, but widespread freezing temperatures appear to not have happened with this event.
Voting: Good - 6 Bad - 0
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07 Oct 2024 08:55 AM
The coolest air of the season to date settled into Iowa overnight with some limited areas of the state likely to have experienced their first freeze. The featured map presents a minimum temperature analysis of the 15 minute interval NWS/NCEP RTMA temperature product. Note that this product is not a true minimum value, but we assume that the 15 minute interval resolution was close enough to capture the minimum. The color ramp and legend intends to highlight temperatures near freezing. The coldest temperatures found within this analysis are over the valley regions of western Iowa, but widespread freezing temperatures appear to not have happened with this event.
Voting: Good - 6 Bad - 0
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Tue Oct 08, 2024
Precip Metrics for Ames
08 Oct 2024 05:30 AM
October has started where September left off with warm daytime temperatures and next to no rainfall. The featured chart presents a number of precipitation metrics over trailing period of days. The x-axis value on each chart represents the period from that given date till 7 October. The present US Drought Monitor analysis for the location is just D0, but a number of short term indicators are now pointing to a worse drought designation. The very wet start to the growing season is still buoying the metrics over the 3-6 month time range and keeping the present situation from being a complete drought disaster. The question at hand though is when is it going to start raining again, which seems to be at least one week out or more at this point.
Voting: Good - 10 Bad - 0
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08 Oct 2024 05:30 AM
October has started where September left off with warm daytime temperatures and next to no rainfall. The featured chart presents a number of precipitation metrics over trailing period of days. The x-axis value on each chart represents the period from that given date till 7 October. The present US Drought Monitor analysis for the location is just D0, but a number of short term indicators are now pointing to a worse drought designation. The very wet start to the growing season is still buoying the metrics over the 3-6 month time range and keeping the present situation from being a complete drought disaster. The question at hand though is when is it going to start raining again, which seems to be at least one week out or more at this point.
Voting: Good - 10 Bad - 0
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Wed Oct 09, 2024
Oct Temps + Dew Points
09 Oct 2024 05:30 AM
Tuesday was yet another day of late with warm daytime temperatures. Such warm weather this time of year is almost always enjoyable as it is rarely accompanied by elevated humidity. The featured chart presents the simple average of dew point temperature at a given air temperature during October for Des Moines. The averages shown for air temperatures above 70°F are just in the lower 50s. With warmer temperatures forecast for this week, dew points are forecast to be below 50°F, so it will be even drier than average for the given temperature. The lack of rain leading to dry landscapes are certainly a big reason why dew points remain low.
Voting: Good - 13 Bad - 0
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09 Oct 2024 05:30 AM
Tuesday was yet another day of late with warm daytime temperatures. Such warm weather this time of year is almost always enjoyable as it is rarely accompanied by elevated humidity. The featured chart presents the simple average of dew point temperature at a given air temperature during October for Des Moines. The averages shown for air temperatures above 70°F are just in the lower 50s. With warmer temperatures forecast for this week, dew points are forecast to be below 50°F, so it will be even drier than average for the given temperature. The lack of rain leading to dry landscapes are certainly a big reason why dew points remain low.
Voting: Good - 13 Bad - 0
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Thu Oct 10, 2024
Hurricane Milton Tornado Warnings
10 Oct 2024 05:30 AM
Hurricane Milton roared onshore over Florida on Wednesday evening. Prior to making landfall, numerous super cell thunderstorms formed with the favorable right front quadrant and produced a prodigious number of tornadoes, including some that are likely going to be rated EF3 and perhaps higher. The approach angle of the Hurricane to Florida, arrival during peak daytime heating, and unusually cold air aloft created a primed environment for tornadoes. The NWS offices in Florida ended up issuing 126 Tornado Warnings for the day. The featured chart presents an IEM accounting for the largest number of Tornado Warnings issued for a US Central date for a single state. Yesterday's event comes in second place behind the super outbreak on 27 April 2011.
Voting: Good - 13 Bad - 1
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10 Oct 2024 05:30 AM
Hurricane Milton roared onshore over Florida on Wednesday evening. Prior to making landfall, numerous super cell thunderstorms formed with the favorable right front quadrant and produced a prodigious number of tornadoes, including some that are likely going to be rated EF3 and perhaps higher. The approach angle of the Hurricane to Florida, arrival during peak daytime heating, and unusually cold air aloft created a primed environment for tornadoes. The NWS offices in Florida ended up issuing 126 Tornado Warnings for the day. The featured chart presents an IEM accounting for the largest number of Tornado Warnings issued for a US Central date for a single state. Yesterday's event comes in second place behind the super outbreak on 27 April 2011.
Voting: Good - 13 Bad - 1
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Fri Oct 11, 2024
Another Aurora for 2024
11 Oct 2024 05:30 AM
After a memorable aurora display back in May that was visible over much of the country, the year 2024 had another spectacular aurora display yesterday evening. Of course, there is no shortage of professionally shot images on the Internet from last night's display, but for content curated by the IEM, the featured image is from the KCRG-TV webcam in Decorah. You can find a YouTube lapse from this camera showing the dancing aurora just after 9 PM. In theory, we may not be done with such displays for the year as the sun continues to produce strong geomagnetic storms.
Voting: Good - 19 Bad - 0
Tags: aurora webcam
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11 Oct 2024 05:30 AM
After a memorable aurora display back in May that was visible over much of the country, the year 2024 had another spectacular aurora display yesterday evening. Of course, there is no shortage of professionally shot images on the Internet from last night's display, but for content curated by the IEM, the featured image is from the KCRG-TV webcam in Decorah. You can find a YouTube lapse from this camera showing the dancing aurora just after 9 PM. In theory, we may not be done with such displays for the year as the sun continues to produce strong geomagnetic storms.
Voting: Good - 19 Bad - 0
Tags: aurora webcam
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Mon Oct 14, 2024
Precip since 1 Sept
14 Oct 2024 05:30 AM
Even with frontal passage over the weekend, no rain was to be found over the state and so continuing the remarkable stretch of dry weather. The featured map presents precipitation totals since the first of September. Much of east central and far western Iowa have reported values below even a quarter of an inch. The dry weather looks to continue this week and some early optimism that rain was on the horizon for the coming weekend is starting to fizzle. There will at least be a storm over the plains for the weekend, so we have to start somewhere!
Voting: Good - 11 Bad - 0
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14 Oct 2024 05:30 AM
Even with frontal passage over the weekend, no rain was to be found over the state and so continuing the remarkable stretch of dry weather. The featured map presents precipitation totals since the first of September. Much of east central and far western Iowa have reported values below even a quarter of an inch. The dry weather looks to continue this week and some early optimism that rain was on the horizon for the coming weekend is starting to fizzle. There will at least be a storm over the plains for the weekend, so we have to start somewhere!
Voting: Good - 11 Bad - 0
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Tue Oct 15, 2024
Phoenix 21 Days of Records
15 Oct 2024 05:30 AM
On Monday, the high temperature for Phoenix, Arizona was 103 degrees and set a record high for the date. It was the 21st consecutive day with a daily high temperature either set or tied for the site. The high temperature on Tuesday is currently forecast well below the record high, so it would appear the streak will end at 21 days. The featured table presents these daily records based on the NWS daily climate reports for the site with data dating back to 1895! An immediate question is if this has happened before at any climate site? The answer is tricky due to considerations for how long of period of record is required prior to considering such a streak as significant. @climatologist49 pointed out that Burlington, IA has a 14 day streak during 1936 that presently exists within the climate record.
Voting: Good - 10 Bad - 0
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15 Oct 2024 05:30 AM
On Monday, the high temperature for Phoenix, Arizona was 103 degrees and set a record high for the date. It was the 21st consecutive day with a daily high temperature either set or tied for the site. The high temperature on Tuesday is currently forecast well below the record high, so it would appear the streak will end at 21 days. The featured table presents these daily records based on the NWS daily climate reports for the site with data dating back to 1895! An immediate question is if this has happened before at any climate site? The answer is tricky due to considerations for how long of period of record is required prior to considering such a streak as significant. @climatologist49 pointed out that Burlington, IA has a 14 day streak during 1936 that presently exists within the climate record.
Voting: Good - 10 Bad - 0
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Wed Oct 16, 2024
Ames Step-Downs
16 Oct 2024 05:30 AM
The calendar says the middle of October, so having the first widespread freeze is certainly expected for Iowa. For Ames, a new season to date coldest temperature was set. The featured chart looks into the number of times after 1 July and until next year's 30 June that the low temperature was colder than any previous season to date temperature (so called step-downs in low temperature). The top panel presents the number of such events each year. The second panel plots the frequency by temperature and the bottom panel plots the frequency by day of the year. For the bottom panel, the algorithm choice of starting on 1 July causes the initial spike as the spin-up for the season happens. Of interest is that on average, there are only about 20 such dates for the given year. So even with all of the colder half of fall and winter season ahead of us, there are likely only about 10 days left whereby a new coldest of the season low temperature will be set. From the glass is half full department.
Voting: Good - 11 Bad - 0
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16 Oct 2024 05:30 AM
The calendar says the middle of October, so having the first widespread freeze is certainly expected for Iowa. For Ames, a new season to date coldest temperature was set. The featured chart looks into the number of times after 1 July and until next year's 30 June that the low temperature was colder than any previous season to date temperature (so called step-downs in low temperature). The top panel presents the number of such events each year. The second panel plots the frequency by temperature and the bottom panel plots the frequency by day of the year. For the bottom panel, the algorithm choice of starting on 1 July causes the initial spike as the spin-up for the season happens. Of interest is that on average, there are only about 20 such dates for the given year. So even with all of the colder half of fall and winter season ahead of us, there are likely only about 10 days left whereby a new coldest of the season low temperature will be set. From the glass is half full department.
Voting: Good - 11 Bad - 0
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Thu Oct 17, 2024
Clouds and First Sub 29°F
17 Oct 2024 05:30 AM
With a strong surface high pressure system overhead, temperatures cooled nicely on Wednesday morning with most of the state experiencing the first freeze of the fall season. The Ames airport bottomed out to 24°F! The featured chart presents a time series of Ames airport cloud coverage reports for a +/- 24 hour period relative to the first fall sub 29°F reading. Each pixel represents an hourly report with tan values indicating missing data. It is very interesting and intuitive to see the lack of cloud cover near the occurrence of such a cold temperature. It is a testament to the importance of radiational cooling for such events as clouds act as the proverbial blanket to buoy near surface air temperatures during night time hours.
Voting: Good - 9 Bad - 0
Tags: firstfreeze clouds
17 Oct 2024 05:30 AM
With a strong surface high pressure system overhead, temperatures cooled nicely on Wednesday morning with most of the state experiencing the first freeze of the fall season. The Ames airport bottomed out to 24°F! The featured chart presents a time series of Ames airport cloud coverage reports for a +/- 24 hour period relative to the first fall sub 29°F reading. Each pixel represents an hourly report with tan values indicating missing data. It is very interesting and intuitive to see the lack of cloud cover near the occurrence of such a cold temperature. It is a testament to the importance of radiational cooling for such events as clouds act as the proverbial blanket to buoy near surface air temperatures during night time hours.
Voting: Good - 9 Bad - 0
Tags: firstfreeze clouds
Fri Oct 18, 2024
Critical Fire Weather
18 Oct 2024 05:30 AM
The Storm Prediction Center is best known for issuing convective watches and outlooks, but they also have a fire weather program and issue a fire weather outlook akin to the convective outlook. Their "Critical" risk threshold for fire weather was forecast over western Iowa on Thursday and such thresholds are somewhat rare for the state. The featured map presents an analysis of the yearly average number of days with such a risk threshold. Areas in white would indicate no such risk over the archive of the product valid for the location. Certainly the further west you go, the greater the chance of such fire weather risks as winds generally increase, humidity decreases and drier vegetation.
Voting: Good - 14 Bad - 0
Tags: firewx
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18 Oct 2024 05:30 AM
The Storm Prediction Center is best known for issuing convective watches and outlooks, but they also have a fire weather program and issue a fire weather outlook akin to the convective outlook. Their "Critical" risk threshold for fire weather was forecast over western Iowa on Thursday and such thresholds are somewhat rare for the state. The featured map presents an analysis of the yearly average number of days with such a risk threshold. Areas in white would indicate no such risk over the archive of the product valid for the location. Certainly the further west you go, the greater the chance of such fire weather risks as winds generally increase, humidity decreases and drier vegetation.
Voting: Good - 14 Bad - 0
Tags: firewx
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Mon Oct 21, 2024
Driest 45 Days
21 Oct 2024 05:30 AM
Some previous hopes for precipitation over this past weekend turned out as empty as the rain gauges over the state with dry and warm weather dominating. The featured chart for today looks at the driest 45 day stretch each season (here defined starting on 1 July) for Des Moines. The bottom left panel shows the frequency of a given day of the year participating within such a period. Such periods are typically limited to the coldest part of the year, so having such a stretch from September into October is rather exceptional, but not without precedent. This analysis indicates that a 45 day stretch during the 1952 season had no measurable precipitation. The caveat with such plots is that sometimes archives of climate data are not great delineating between zero precipitation and precipitation reports as missing / not reported, so caveat emptor!
Voting: Good - 11 Bad - 0
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21 Oct 2024 05:30 AM
Some previous hopes for precipitation over this past weekend turned out as empty as the rain gauges over the state with dry and warm weather dominating. The featured chart for today looks at the driest 45 day stretch each season (here defined starting on 1 July) for Des Moines. The bottom left panel shows the frequency of a given day of the year participating within such a period. Such periods are typically limited to the coldest part of the year, so having such a stretch from September into October is rather exceptional, but not without precedent. This analysis indicates that a 45 day stretch during the 1952 season had no measurable precipitation. The caveat with such plots is that sometimes archives of climate data are not great delineating between zero precipitation and precipitation reports as missing / not reported, so caveat emptor!
Voting: Good - 11 Bad - 0
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Tue Oct 22, 2024
Days to 0.10" Precip
22 Oct 2024 05:30 AM
The dry weather this fall season has been remarkable. The featured map attempts to illustrate the recent dryness by accumulating the number of days until just one tenth of an inch of precipitation is accumulated. Note that this map does not include the rain that fell since midnight this morning. This is a way to show the locations of the state that have been the driest for the longest period. A number of locations are analyzed in the 45 to 60 day range, including areas in east central and northwestern Iowa. The good news is that the forecast to end October and to start off November looks to have a number of precipitation chances as a pattern shift appears to be in the works.
Voting: Good - 15 Bad - 0
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22 Oct 2024 05:30 AM
The dry weather this fall season has been remarkable. The featured map attempts to illustrate the recent dryness by accumulating the number of days until just one tenth of an inch of precipitation is accumulated. Note that this map does not include the rain that fell since midnight this morning. This is a way to show the locations of the state that have been the driest for the longest period. A number of locations are analyzed in the 45 to 60 day range, including areas in east central and northwestern Iowa. The good news is that the forecast to end October and to start off November looks to have a number of precipitation chances as a pattern shift appears to be in the works.
Voting: Good - 15 Bad - 0
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Wed Oct 23, 2024
2024 Daily Departures
23 Oct 2024 05:30 AM
The featured chart presents the 2024 daily high and low temperatures for Ames along with NCEI 1991-2020 climatology and the departures between the two. Of immediate notice is the two week period in January that we experienced winter last year with the rest of the season being mostly above average. The warm high temperature departures as of late have been quite large and there's an interesting difference to be noticed between those of July and August vs September and October. For the former period, you'll notice how closely the high and low temperature departures track each other vs a larger spread during the later period. The difference is due to humidity levels. Dry air will heat more easily during the day and cool more easily at night. Increased atmospheric humidity will temper the two aforementioned processes with air mass warming being able to more easily persist overnight.
Voting: Good - 10 Bad - 0
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23 Oct 2024 05:30 AM
The featured chart presents the 2024 daily high and low temperatures for Ames along with NCEI 1991-2020 climatology and the departures between the two. Of immediate notice is the two week period in January that we experienced winter last year with the rest of the season being mostly above average. The warm high temperature departures as of late have been quite large and there's an interesting difference to be noticed between those of July and August vs September and October. For the former period, you'll notice how closely the high and low temperature departures track each other vs a larger spread during the later period. The difference is due to humidity levels. Dry air will heat more easily during the day and cool more easily at night. Increased atmospheric humidity will temper the two aforementioned processes with air mass warming being able to more easily persist overnight.
Voting: Good - 10 Bad - 0
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Thu Oct 24, 2024
Lacking Soil Moisture
24 Oct 2024 05:30 AM
The featured chart presents weekly USDA NASS estimated percentage of topsoil by state with a poor or very poor moisture status. Each year's data is plotted with three years highlighted over six states. The lack of rain this fall season is taking a serious toll on soil moisture with six states showing a worsening status. Thankfully, the very dry weather generally started after the agricultural crops reached maturity, albeit there was a yield hit for soybeans which could have used some more late season rainfall. Anyway, this can be readily seen with the 2024 time series showing very little soil moisture stress until August for western corn belt states.
Voting: Good - 10 Bad - 1
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24 Oct 2024 05:30 AM
The featured chart presents weekly USDA NASS estimated percentage of topsoil by state with a poor or very poor moisture status. Each year's data is plotted with three years highlighted over six states. The lack of rain this fall season is taking a serious toll on soil moisture with six states showing a worsening status. Thankfully, the very dry weather generally started after the agricultural crops reached maturity, albeit there was a yield hit for soybeans which could have used some more late season rainfall. Anyway, this can be readily seen with the 2024 time series showing very little soil moisture stress until August for western corn belt states.
Voting: Good - 10 Bad - 1
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Fri Oct 25, 2024
Iowa Hail Reports
25 Oct 2024 05:30 AM
Rain and even thunderstorms returned to Iowa on Thursday! Much needed rainfall fell over mostly the southeastern portion of the state. Some of the stronger storms produced hail. The featured calendar plot presents the number of preliminary hail reports of at least one inch in diameter by day for Iowa since 1 July. The lack of such reports over the past three months is another sign of how few thunderstorms there have been over this period.
Voting: Good - 13 Bad - 0
Tags: hail
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25 Oct 2024 05:30 AM
Rain and even thunderstorms returned to Iowa on Thursday! Much needed rainfall fell over mostly the southeastern portion of the state. Some of the stronger storms produced hail. The featured calendar plot presents the number of preliminary hail reports of at least one inch in diameter by day for Iowa since 1 July. The lack of such reports over the past three months is another sign of how few thunderstorms there have been over this period.
Voting: Good - 13 Bad - 0
Tags: hail
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