June 29, 1998 Iowa Derecho


Area affected by the June 29, 1998 derecho (outlined in blue). Approximate two-hourly positions (CDT) of the derecho gust front indicated by curved black lines. Blue “+” symbols indicate locations of wind damage or wind gusts (measured or estimated) above severe limits (58 mph or greater). Severe hail denoted by green circles; tornadoes by red dots or lines. Image Courtesy of Storm Prediction Center. http://www.spc.noaa.gov/misc/AbtDerechos/casepages/jun291998page.htm

An incredible complex of severe thunderstorms produced widespread extreme straight-line wind damage across much of Iowa causing over $150 million in damages. $100 million of that total occurred in Polk County alone. This included the $11 million in damages initially claimed in Johnston and $726,000 in West Des Moines. Statewide, 80 homes were completely destroyed, 559 sustained severe damage, with 1416 other homes receiving moderate damage from the storm.

Areas in central Iowa particularly hit the hardest were from just northwest of Des Moines through the metro but also extended east southeast to the Mississippi River before moving on through Illinois, Indiana, and Kentucky. From the image above, this derecho lasted for several hours and brought swath of damage throughout the Midwest. In fact, this complex of storms originated in northern Nebraska during the early morning hours then moved east southeast into central Iowa where it interacted with changing atmospheric conditions and intensified further. A tornado cut an 11 mile path across Crawford County damaging dozens of residences and numerous outbuildings. Several other more brief tornado touchdowns were reported as the storms cut a path across Iowa, along with occasional large hail ranging in size up to 2.5 inches in diameter at Des Moines, but the majority of the damage was produced by very severe straight-line winds. The line of storms produced winds of 70 to 90 mph along its entire length, with embedded swaths of even stronger winds in some areas.

In the Des Moines metro area one such swath extended from around Granger through Johnston and northeastern Des Moines, with post-storm damage surveys indicating wind gusts of around 120 mph or damage to justify F2 winds. Trucks and heavy construction equipment were blown over on the interstates and hundreds of homes and other buildings were unroofed or otherwise severely damaged in the metro with countless reports of trees falling on homes. Further east the storms produced more extreme wind damage near and south of Iowa City, with an observer at Muscatine recording a wind gust of 104 mph and an unofficial instrument in Washington measuring an incredible 123 mph gust, which is the highest unofficial wind gust ever measured in Iowa. In Iowa City several cars of a freight train were blown off a railroad bridge over the Iowa River and plunged into the water below (See video below courtesy of KCRG-TV9). At the height of the storm approximately 500,000 people in Iowa were without power and in some areas electricity was not restored for nearly a week. Thousands of homes and buildings were damaged across the state and at least 125 people were injured by flying debris but fortunately there were no fatalities.

Strong winds bout to hit the DMX WSR-88D at 1:40 p.m. causing a door to the radar dome to blow open, resulting in taking the radar offline for 10 minutes.

Strong winds bout to hit the DMX WSR-88D at 1:40 p.m. causing a door to the radar dome to blow open, resulting in taking the radar offline for 10 minutes.


Click here for a more detailed write-up of the event in Polk County and central Iowa: http://www.weather.gov/media/dmx/SocialMedia/19980629_EventNarrative_FromStormData.pdf

Storm Prediction Center Event Summary: http://www.spc.noaa.gov/misc/AbtDerechos/casepages/jun291998page.htm

The Quad Cities NWS was also affected by the Derecho: http://www.weather.gov/dvn/ev19980629svr

May 27-29, 1947 Snowstorm

One of the most unusual weather events in Iowa history occurred as an intense low pressure system moved northeast across Missouri and into the Great Lakes region, passing over the far southeastern corner of Iowa. Meanwhile an unseasonably cold area of high pressure spread down the northern plains bringing record breaking cold temperatures to much of the region. A heavy snow storm tracked along the northwestern side of the low across eastern Wyoming and Colorado, Nebraska, Iowa, Wisconsin, and into northern Michigan from May 27-29 producing unprecedented snowfalls for so late in the spring. In Iowa the storm struck on the 28th with most precipitation in the south coming in the form of thunderstorms and rain, sometimes mixed with sleet and snow, while across about the northern half of the state the precipitation fell almost entirely as snow. In Iowa, measurable snow was recorded at most locations north of a line from Council Bluffs to Dubuque with reported accumulations including an incredible 10.0 inches at Le Mars, 8.0 inches at Cherokee, 7.5 inches at Waukon, 6.0 inches at Alton and Hawarden, 5.0 inches at Cushing, Iowa Falls, Milford, and Northwood, 4.5 inches at Mason City, 2.0 inches at Waterloo, and a trace at many locations including Des Moines. In Nebraska several locations received 10 to 12 inches of snow and in Wisconsin 8 to 10 inches fell in a narrow band from Gays Mills to Green Bay. To put into perspective how unusual this event was, no snow has ever been recorded anywhere in Iowa at a later date in the spring. The total of 10.0 inches at Le Mars was the highest snow accumulation on record in Iowa at any time in the month of May until it was bested by the storm of May 1-3, 2013. A series of heavy rains in the following several weeks combined with the snow-melt from this storm to produce historic flooding across many parts of Iowa in June of 1947.

May 27-29_1947 Snow Storm

April 14 – 1886 Tornado Outbreak

On April 14, 1886, a widespread and deadly tornado outbreak ripped Minnesota, Iowa, Kansas, Missouri and Texas.  At least 19 tornadoes touched down and ripped across Iowa. Several of these tornadoes were said to produce significant damage including one that produced F4 damage, killing 3 people and injuring 18 others. This F4 tornado traveled from near Griswold, Iowa (Cass County) through Audubon and Guthrie Counties destroying most of Coon Rapids, Iowa before dissipating near Churdan, Iowa. Another tornado produced F3 damage in Taylor and Adams counties injuring at least 15 people. Further north in Minnesota, several significant tornadoes developed and probably the most notable tornado of the day was estimated to be a F4 that tore up the cities of Sauk Rapids, Saint Cloud, and Rice, Minnesota. This F4 tornado killed 72 people and injured more than 200 and caused over $400,000 in damages. In 2015 dollars, that would be roughly $10.4 million dollars. This has been Minnesota’s deadliest tornado to date.


The record book from the Des Moines Observer on April 14, 1886 mentions there was a tornado reported in the western part of the state.

Sauk Rapids, MN after the devastating F4 tornado on April 14, 1886. Image courtesy Wikipedia.

Sauk Rapids, MN after the devastating F4 tornado on April 14, 1886.

Sauk Rapids, MN after the devastating F4 tornado on April 14, 1886. Image courtesy Wikipedia.

Sauk Rapids, MN after the devastating F4 tornado on April 14, 1886.

Snow Depth at Des Moines – Spring 1960

Number of Consecutive Days with a snow depth greater than or equal to 12 inches for Des Moines, Iowa.

Number of Consecutive Days with a snow depth greater than or equal to 12 inches for Des Moines, Iowa.

On the First Day of Spring in 1960 (March 21), marked the 27th consecutive day on which at least a foot of snow was measured on the ground at Des Moines. This established an all-time station record that still stands today. Des Moines actually came very close to this record in 2010 but fell 2 days shy of tying the record. At any rate, this incredible streak began on February 24, 1960 after several consecutive days of snowfall that pushed the snow depth to 13 inches. So for nearly four weeks, a combination of persistent cold and additional snowfalls prevented the snow pack from melting and compacting. Over the 27 days from February 24th through March 21st, measurable snow fell at Des Moines on 16 days and the temperature only rose above freezing twice when highs of 33°F on the 18th and 37°F on the 21st occurred. During the last week of March a warming trend finally developed and temperatures reached 60°F on the 29th and the last of the snow melted the following day on the 30th. Unfortunately, all this snow melt led to flooding on the Raccoon, Des Moines, and Skunk Rivers as snow depths ranged from 17 to 19 inches withing these three basins on March 15th but were zero by the 31st! With such a deep persistent snow pack in place March 1960 was also abnormally cold. At Des Moines, the average temperature for the month was only 21.4°F making it the coldest March on record at that location.

Average Temperature Departure from Mean from February 27 to March 21, 1960.

Snowfall from February 27 to March 21, 1960 for Iowa.

25th Anniversary of the March 13, 1990 Tornado Outbreak

March 13, 2015 marks the 25th anniversary of the tornado outbreak that spawned 59 tornadoes across Iowa, Kansas, Missouri, Nebraska, Oklahoma and Texas. The largest and most destructive tornado was the F5 tornado that demolished Hesston, Kansas. A more detailed write-up is available from our colleagues at the National Weather Service Office in Wichita, Kansas: http://www.crh.noaa.gov/ict/?n=hesston
In Iowa, multiple severe thunderstorms swept across the state and produced 14 tornadoes, large hail to the size of golf balls, and wind gusts as high as 75 mph. The most destructive tornado in Iowa was an F4 that struck Prairieburg in northeast Linn County and was on the ground for 19 miles into Jones and Delaware Counties. An F2 hit Ankeny, injuring 15 people and producing 6 million dollars in damage. The largest hail reports were near Elvira and 75 mph wind gusts caused damage near Little Sioux and Logan. This was part of a wild stretch of weather in early to middle March of 1990 that saw a significant ice storm followed by several severe weather and tornado outbreaks then a big snow storm, all in a nine day stretch.

Here’s another great write-up on the March 13, 1990 tornado outbreak from the NWS Office in Hastings, Nebraska: http://www.crh.noaa.gov/gid/?n=march13,1990tornadoes

Iowa H.S. State Basketball Tournament Snow Facts

Snowfall and the Girls and Boys High School State Basketball Tournaments go hand in hand. Often, we receive inquiries about expected snowfall during one or both of these tournaments. March snowfall in Iowa is quite common and to be expected. The nice thing about snowfall in March is that it won’t stay around long.

The High School State Basketball Tournaments have moved around from town to town during their history, but this quick look at snowstorms during the tournaments will just examine climatological data for Des Moines from 1950 to the present and for the first two weeks of March. These two weeks should generally capture any snowstorms over the last 65 years that might have affected travel to and from the tournaments.

The following tables depict the top ten 24-hour snowfall totals, 48-hour snowfall totals and Week 1 and Week 2 snowfall totals for Des Moines from the period 1950-2014.


The table above shows that in Des Moines, only two, single days and four, two-day periods over the last 65 years have received snowfalls greater than six inches in the first week of March. Six inches of snow is generally the point at which the National Weather Service would issue a Winter Storm Warning. In fact, there were only four years with two-day totals greater than six inches: 1959, 1965, 1982, 2007. In other words, during this 65 year period, there were only four snowstorms, each spanning two days that brought snowfall greater than six inches; or only 6% of the time. The other 94% of the time, in Des Moines, you can expect fairly good weather the first week of March.


Similarly, for the second week of March, there were only three, single days and five, two-day periods over the last 65 years that Des Moines has received snowfalls greater than six inches. Two of the five two-day periods of snow greater than six inches occurred on three consecutive days: March 10-12, 1951. Again, around 95% of the time, in Des Moines, during the second week of March, you can expect relatively quiet weather.



1951 bubbles to the top of the heap for the weekly snowfall totals for the second week of March, although the more recent years of 1999 and 1998 rank second and third, respectively. The first week of March in 1965 also brought a lot of snow, with the second and third rankings somewhat less. Once again, only six years of the last 65 (10%) during the first week in March have experienced greater than six inches of snow. The second week of March is the same with 6 out of 65 years (10%) having 6 inches or more of snow during the week. Overall, while central Iowa might in fact have a big snowstorm in the first half of March, it’s much more likely that little to no snow will fall and ruin your Basketball Tournament travel plans. Before heading out, remember to check the latest forecasts and travel conditions so you may make informed decisions regarding travel and types of clothing to pack. Above all, have a safe and fun time.

Blog post by Craig Cogil – NWS Des Moines

Historic January 24, 1967 Tornado Outbreak

Today, January 24, is the 48th anniversary of the January 24, 1967 Tornado Outbreak that struck eastern and southeastern Iowa and portions of Missouri, Illinois, and Wisconsin. There were at least 13 tornadoes in Iowa with many of these producing significant F2 or F3 damage. Two tornadoes struck Lee County resulting in 10 injuries, and one of those tornadoes produced F3 damage and killed a young child just west of Fort Madison. Another tornado produced F4 damage just across the border in northeastern Missouri before entering Davis County. Later that evening, a strong cold front swept across the state and by the 26th, snow fell across about the southern half of Iowa with snowfall amounts ranging up to 13.5 inches at Burlington, only two days removed from the significant tornado outbreak in the same area. This likely made for a difficult clean-up and storm damage assessment.

To put the extremely unusual nature of this tornado outbreak into perspective, this is the only date in January on which a tornado has ever been recorded in Iowa.

The Quad Cities and Saint Louis NWS Offices have some fantastic detailed write-ups about this event:

Blog Post by Kenny Podrazik and Jim Lee – NWS Des Moines

Week of Christmas 2009 Winter Storm/Blizzard

Three Day Water Vapor Loop – December 23-25, 2009

A major winter storm system stalled over the central United States during the week of Christmas 2009 and brought multiple rounds of wintery precipitation over Iowa from December 23-26, 2009. The first round of precipitation fell in the form of freezing drizzle or freezing rain during the early morning hours on the 23rd over central Iowa. A sharp gradient set up across Iowa as snow developed over northwest Iowa, rain in southeast Iowa, while freezing rain and sleet fell in between through the afternoon and evening hours on December 23. The precipitation finally transitioned to all snow from west to east on the 24th and 25th before tapering off on the 26th. The storm was so wrapped up around itself that the temperatures on Christmas Day across Iowa were flipped as north-central to northeast Iowa were in the 30s and the west-central to southwest portions of the state were only in the lower teens.

This storm produced heavy snowfall across western to northwestern Iowa, with a total of 24.0 inches at Spencer shattering the previous storm total record at that location by a full 5 inches. In fact, combined with several other winter storms in December 2009, Spencer set an all-time record monthly snowfall total for Iowa with 40.0 inches for December. Other snowfall amounts from the Christmas Week storm included 16.0 inches at Little Sioux, 15.7 inches at Hawarden, and 15.5 inches at the Sioux City airport. Further south and east of the heavy snow band, a substantial amount of ice accrual crippled several counties in west-central Iowa and the hardest hit counties were Audubon, Crawford, Carroll, Guthrie, and Greene. In these locations, around a half an inch to nearly an inch were reported and resulted in multiple down power lines, broken tree branches, and made driving extremely hazardous. Other portions of central Iowa received lighter ice amounts, generally around a tenth of an inch or less, but there was enough to cause significant travel problems on December 23 to 24, 2009. In addition to the heavy snow and freezing rain, very strong north winds of 25 to 35 mph developed on the 24th and continued into Christmas Day and either caused significant blowing and drifting of snow or blew down ice covered trees and power lines. Thousands of residents lost power due to this storm for several days, especially over west-central Iowa. The Governor of Iowa declared a state disaster for several counties in western Iowa. December 2009 finished as the second snowiest month on record in Iowa in terms of statewide average snowfall, only behind December of 2000.


Snowfall totals from the Christmas Storm 2009.





Cass County on December 29, 2009

Cass County December 28, 2009

Jamaica, Iowa in Guthrie County on December 23, 2009


Cass County December 28, 2009>

Jamaica, Iowa in Guthrie County December 23, 2009>

Carroll County December 30, 2009

Surface observations at 11 am CST on Christmas Day 2009. Image courtesy of IEM.

Surface temperature analysis at 9 am December 25, 2009. Image courtesy of IEM.

The Iowa DOT Road Conditions at 12:21 am December 23, 2009. Image courtesy of IEM, Iowa State Patrol and IDOT.

Blog Post by Kenny Podrazik – NWS Des Moines

A Blizzard that People Remember

The Blizzard of December 8-9, 2009

It’s hard to believe that it has been 5 years since a large blizzard blasted Iowa on December 8-9, 2009. NWS Des Moines Meteorologists still reminisce and discuss this high-impact event as it produced some memories they won’t soon forget. For instance, it took a few forecasters at least 3 times longer to make it to work to cover their shift on that snowy Tuesday into Wednesday and a couple even stayed the night in the office on cots to wait out the storm! A recently hired intern had the task of measuring snowfall in the blizzard and when she went out at midnight Tuesday night on the 8th, she learned the hard way to always bring her security card with her in order to re-enter into the building as she locked herself out. Other forecasters remember being snowed-in and digging out 6 foot drifts from their driveways on Wednesday.

The storm began early Tuesday morning on December 8th when light to moderate snowfall extended across central to southern Iowa. The snow slowly spread over the rest of the state and intensified during the afternoon and evening hours and significantly affected the Des Moines rush hour Tuesday night. Strong northwest winds increased to 25 to 35 mph and gusted to over 50 mph at times by late Tuesday night and continued into early Wednesday morning. There were even a couple of reports of wind gusts to 60 mph overnight Tuesday into Wednesday. The strong winds and heavy snow produced large drifts throughout the state, with several reports over 6 feet! Visibility became reduced significantly as widespread whiteout conditions were observed from the overnight hours Tuesday into Wednesday before improving Wednesday afternoon. Travel became impossible or nearly impossible across much of Iowa due to the large drifts and widespread white-out conditions (See Figure 1).

The powerful storm dropped anywhere from 8 to 17 inches over much of Iowa with the highest swath oriented southwest to northeast across the state (See Figure 2). In fact, the statewide average storm total snowfall was 10.2 inches became the highest storm total since 1971 and the third-highest on record in Iowa. Some of the higher totals around the state included 15.5 inches in Des Moines, 16.0 inches in Atlantic and Belle Plaine, 16.2 inches in Corning and Osceola, and a whopping 17.0 inches in Knoxville. Des Moines recorded its this fourth-heaviest snow storm on record behind the December blizzard of 1888, the New Year’s storm of 1942, and the blizzard of March 2004.

The severity of the storm affected the surrounding states of Iowa as well. Blizzard warnings covered portions of eastern Nebraska, southern Minnesota, northern Missouri, the southern half of Wisconsin, and far northeast Kansas. All 99 counties in Iowa were under a blizzard warning Tuesday night into Wednesday (See Figures 3 and 4). A temperature gradient across Iowa late Tuesday night was about 25 degree difference from southeast to northwest Iowa (See Figure 5). By Wednesday afternoon, temperatures plummeted into the single digits to around 10 above, leading to wind chill values as low as -31F at Mason City on the 9th. The snow finally tapered off by Wednesday afternoon but the howling winds continued into Wednesday night. High pressure built into the region and brought clear skies on Thursday allowing the large swath of snow to be seen on visible satellite (See Figure 6). If residents of Iowa remember, this big blizzard was just the beginning of a very active winter with frequent snowfalls and persistent deep snow pack across the state.

Figure 1: Road conditions Wednesday morning December 9, 2009. Image courtesy of Iowa State Patrol, IDOT, and IEM.

Figure 2: Total snowfall amounts across Iowa from the December 8-9, 2009 Blizzard. Snow totals ending at 7 pm on December 9, 2009.

Figure 3: The blizzard had a huge impact across much of the central United States. Image is courtesy of MRCC.

Figure 4: All 99 counties in Iowa had a blizzard warning in effect at 5pm on December 8, 2009.

Figure 5: Temperature difference across Iowa at 2 am Wednesday morning December 9, 2014. Temperatures in the lower 30s were found in southeast Iowa while the northwest part of the state dropped to 5 to 10 above. Image via IEM.

Figure 6: Visible satellite image from Thursday December 10, 2009 shows nothing but snow across much of the Midwest and Plains except for a few clouds over eastern Iowa.

Snow removing equipment in Mahaska County. Photo from Mahaska County Emergency Management.

Sundog on December 9, 2009.

Snowy office.

North side of Des Moines. Photo from Matt Kelley.

Grimes, IA on December 9, 2009.

Large drift in front of the NWS Des Moines office.

Blog post by Kenny Podrazik – NWS Des Moines

Tornado Survey – “The Old School Way”

Take yourself back 75 years to August 10, 1939 when World War II was less than a month from getting underway, the U.S. was slowly climbing out of the Great Depression and on the brink of war, the Studebaker Champion was introduced and cost about $660 (or $11,312 in 2014), and the Cubs actually had a winning record! Sorry Cubs’ fans. The country was just learning about ALS or Lou Gehrig’s disease as he was just diagnosed and had to retire from baseball that summer. The price of gas was $0.10, a pound of hamburger was $0.14, and a loaf of bread was $0.08. The average cost of a new house in 1939 was $3800 but now, the average cost of a new home in 2014 is $339,100 (per U.S. Census).

Okay, so you’re back in August 1939 in Iowa when no weather radar coverage or tornado warnings were available to meteorologists. Folks literally could say “It struck without warning” and be honest about it! They still did damage surveys, but the Fujita scale wouldn’t be introduced until 1971.  So when C.D. Reed and/or S.E. Decker, from the Iowa Department of Agriculture or IDA (See Figures 1a and 1b) had the daunting task of surveying three destructive tornadoes that occurred on August 10, 1939 in central Iowa, they did an amazing job (See Figure 2).  Back then, surveying included talking with eyewitnesses hit by the tornado and whatever sort of geodetic survey equipment they had available. They had limited resources, but the detail of what buildings were hit, livestock killed, or persons injured was phenomenal. Granted there were less people and fewer buildings to destroy, but traveling and communication was more cumbersome in 1939 than 2014; especially since the survey covered several counties.

Figure 1a: C.D. Reed Author of the Iowa monthly climate review for August 1939.

Figure 1a: C.D. Reed Author of the Iowa monthly climate review for August 1939.

Figure 1b: S.E. Decker was the author of the damage survey or storm section in the Climatological Data: Iowa Section.

Figure 1b: S.E. Decker was the author of the damage survey or storm section in the Climatological Data: Iowa Section.

The hardest hit counties were Adair, Clark, and Warren from the tornadoes while Polk County endured significant damage due to heavy rainfall. Well what do you know  – heavy rain in August in Iowa? There’s a shocker.  Another county, Montgomery, was hit hard with large hail as noted on the tornado track from Figure 2 and suffered $10,000 worth of crop damage.

August 10-1939 TornadoPaths-resize

Figure 2: hand drawn maps of the tornado paths and hail swaths on August 10, 1939.

The first and second tornadoes occurred in Shelby and Adair Counties respectively. The twister in Shelby County damaged buildings on five farms resulting in a loss of $12,000 (see inflation rate table below) and injured one person, Mrs. Pete Anderson, according to the report.

The Adair County tornado started about 3:30 p.m. near the Summerset Township and traveled northeast through Summerset and Prussia to just east of Fontanelle, Iowa. Miss Mildred Bakerink was fortunate to photo the tornado when it was about 3 miles northeast of her location near Prussia (See Figure 3). Reports suggested the early life of the tornado that “the storm of pendent cloud was shaped more like a cone with a wide V-top.”  The survey determined the tornado path was about “12 miles long and 80 rods wide.” A rod is equivalent to 5 ½ yards or 16 ½ feet in length.  Hence, the tornado width was roughly 440 yards (1320 feet) wide or a quarter of a mile. That’s a pretty significant tornado. To compare it to a recent tornado that occurred in Iowa, the “Belmond” Tornado that passed through the north side of Belmond on June 12, 2013 was 200 yards wide with path length of 6.2 miles. This tornado was rated an EF-3 tornado with a 155 mph peak wind speed. You can draw your own conclusions on where to rate the Adair County Tornado from August 10, 1939. To help you out, damage was estimated to buildings on six farms ranged from $5,000 to $10,000 while the damage to crops, stock, implements “amounted to several thousand dollars”, according to the IDA report. Luckily, there was only one injury and no deaths.


The third and most destructive tornado was on the ground for roughly 35 miles and it originated southwest of Osceola, in Clarke County, and finally dissipated near Milo in Warren County.  The damage surveyor, likely C.D. Reed, visited Liberty Center where several eyewitnesses said they could see five funnel clouds visible at one time southwest of town. There were also several reports from Osceola that suggested seeing the five funnel clouds at the same time.  In fact, a writer from the Osceola Tribune depicted the funnel cloud as “bounding around like a rubber ball, alternately lifting and lowering.” Here’s how the eyewitnesses from Liberty Center described the funnels:

“…as being close together and joined to a common dark cloud mass. They were said to be suspended in the air without touching the ground as long as they remained separated, but that upon joining or merging the remaining funnel grew in length and extended down to the ground.”

This sounds a lot like a what modern day meteorologists call a multi-vortex tornado. It certainly did some damage to Clarke and Warren Counties. The IDA report said “buildings were demolished on at least ten farms” in Warren County. There were 18 of 22 buildings, on one livestock farmstead, “wrecked or seriously damaged.” There was a stretch of corn, roughly a mile wide and 15 miles long, which was completely flattened. Several trees were snapped or uprooted, power and telephone lines blown down, and most fences blown away in the tornado path. The description of the damage near Liberty Center gets even more detailed (See Figure 4). The total damage from the storm, including heavy rain and straight-line winds, in Warren County was estimated to be at least $102,000 as the IDA report stated “several thousand dollars more” to furniture, telephone lines, crops, etc.  There were several injuries but no related deaths. The table below shows the damage adjusted for inflation from 1939 to 2014.

August 10-1939 DamageDescription

Figure 4: very detailed description of the the tornado damage near Liberty, Iowa.

The surveyor calculated the speed of the storm itself at around 40 mph by determining when and where it originated and when and where it dissipated. Something we still do today but with the aid of radar data, satellite imagery, and aerial photos.  The surveyor estimated the “rotary winds indicated at least hurricane velocity of about 75 miles per hour.” From the description of the damage, there’s little doubt the peak wind speeds where likely higher.

As far as the meteorological setup, a surface analysis on the morning of the storms (See Figures 5-7) suggested a warm front draped across Arkansas into eastern Oklahoma. However, further surface analysis along with the description from the IDA report, the warm front extended north-northwest and connected to the cold front near the Grand Island area.  The storms developed along the warm front by the late afternoon as its surged north throughout the day. The cold front, according to the report, pushed through the Des Moines area around 6:30 p.m. time frame.

A fine job done by the folks at the Iowa Department of Agriculture, which was likely down by either C.D. Reed or S.E. Decker or both, on the storm survey from August 10, 1939.


Figure 5: North America Synoptic Weather Map on the morning of August 10, 1939 at 1230 UTC or 6:30 am.


Figure 6: Zoomed in morning surface analysis on the Corn Belt and Central Plains.


Figure 7: CONUS surface analysis on August 10, 1939 at 6:30 am. The map shows the area of low pressure over northern Kansas and a boundary extending from southwest to northeast Iowa. It also depicts thunderstorms over South Dakota, western Nebraska, and far northwest Iowa.

Tornado Damage Adjusted for Inflation

Township County Type of Damage 1939 Cost 2014 Cost
Polk Shelby Buildings $12,000 $205,700
Polk Shelby Crops $1,000 $17,140
Polk Shelby Livestock $100 $1,710
Red Oak Montgomery Crops $10,000 $171,400
Summerset/Prussia Adair Buildings $5,000-10,000 $85,700-171,400
Near Osceola Clarke Buildings $10,000-15,000 $171,400-257,100
Near Osceola Clarke Crops $5,000 $85,700
Near Osceola Clarke Livestock $500 $8570
Near Liberty Center Warren Buildings $75,000 $1.3 million
Near Liberty Center Warren Livestock $2,000 $34,280
Near Liberty Center Warren Crops $25,000 $428,500

Inflation rates rounded and based off cumulative rate of 1614.0%



Blog post by Kenny Podrazik – NWS Des Moines