Spotter Training – Spring 2017

Severe Storm Spotting classes are underway this spring.  Classes are available for central Iowa communities through the end of April and we hope you’re able to find one near you.  You can find a listing of upcoming classes here: 2017 Spotter Training Schedule.  If you can’t make a class, you can find plenty of storm spotting resources on our homepage. Below is a quick review on the importance of severe storm spotting and the different avenues to report severe weather to the National Weather Service. 

Reporting Severe Weather

Reporting severe weather is essential! Regardless of the reporting method, each report must include the time & location of the event (and direction looking if applicable). Pictures tell a thousand words, but remember to include when and where the weather occurred! If you do send photos, please let us know if you grant permission for us to use them in future spotter talks and outreach presentations.

How to Report:

Online: Use our online weather reporting form! For reporting tornadoes, please use our 1-800-SKYWARN telephone line.

Email: – A great way to include pictures & video.

Text Message: (515)-240-5515 – Text us reports and your phone photos/videos.

Telephone: 1-(800)-SKYWARN – Must have been through severe weather spotter training and belong to a spotter network to use this line! Refer to materials received during spotter training.

Facebook: Visit our Facebook page and post a severe weather report to our wall.

Twitter – Tweet us your reports by including the #iawx or #nwsdmx hashtag or send them directly to @NWSDesMoines.

Amateur Radio – The National Weather Service group amateur radio call-sign is KØDMX.

A Recap of 2015 Central Iowa Tornadoes

By Kevin Skow, Meteorologist Intern

Overall, the 2015 Iowa tornado season has been relatively quiet up through the end of August. A preliminary total of 30 tornadoes have been recorded for the year throughout the state, which is below the average of 46 tornadoes typically seen in a given year. Iowa’s tornado season historically peaks in the months of May and June, though late season outbreaks can occur well into November. With the bulk of the season behind us, here is a recap of some notable tornadoes to strike central Iowa this year.

May 10: Carroll and Calhoun Counties

The first significant tornado of the season to hit central Iowa occurred on the late afternoon of May 10. A small and compact supercell overrode a warm front and, aided by high low-level instability and shear, produced when has been up to this point the longest-tracked tornado of the season for Iowa. This very visible EF1 tornado touched-down at 7:10pm northwest of Lidderdale in northern Carroll County and tracked to the NNE. The broad but thankfully weak tornado made a direct hit on the town of Lake City at 7:32pm, damaging the roofs of a number of homes and businesses, including the school. The tornado continued churning northeastward across rural Calhoun County, hitting several farmsteads along its way, but damage was relatively light. The dying tornado passed just to the west of Rockwell City shortly after 7:50pm and finally dissipated northwest of town at 8:00pm. It travelled for 23.5 miles during the 50 minutes it was on the ground.Radar

The tornado quickly lofted dust and other debris high enough to be sampled by the Doppler radar in Des Moines, 70 miles away and at a radar beam height of 5,000 ft. This shows up as the yellow and green shaded region on the correlation coefficient radar image at right, also provided with a velocity image (left) to show the location of the tornado. This tornadic debris signature reached up to 16,000 ft into the storm! Videos shot of the tornado, as well as satellite imagery of the track in the days afterwards, showed that this tornado was multi-vortex in nature, with the worst damage concentrated in small streaks.

Mid-May to Mid-June

The middle part of May to the middle of June, typically the peak of Iowa’s tornado season, was only characterized by a few weak, but somewhat rare, early morning tornado episodes. The first event early on the morning of May 17 was also responsible for producing a downburst that derailed an 80-car train near Osceola. The five short-lived tornadoes that occurred afterwards were weak but did damage a few farmsteads in Madison and Dallas counties.


Another early morning tornado event took place between 1 and 2 am on June 7 across Webster, Boone, and Story counties. Four very brief tornadoes touched down along the leading edge of a squall line, one of which moved through far southern Ames and caused tree (photo on right) and light building damage. A squall line was also responsible for strong EF1 tornado on the afternoon of June 20 near Eddyville.


June 22: Marion, Lucas, and Monroe Counties

EF3MonroeCountyThe streak of weak tornadoes came to an end on June 22. A powerful supercell spawned a tornado over far southern Marion County shortly after 5:00pm, which then clipped northeastern Lucas County before strengthening and tracking into northwest Monroe County. While it thankfully stayed out over rural areas of the county during its half hour long life, this now 500 to 600 yard wide EF3 tornado did make a direct hit on one farmstead, completely destroying the house and several outbuildings (photo). Thousands of trees were destroyed by this rain-wrapped tornado as it traversed the hilly and wooded regions of Monroe County on its 11 mile track. The tornado lifted eight miles northwest of Albia, but a second EF2 tornado developed just to the west of town and hopscotched through the southwest part of the city, heavily damaging several businesses and homes.

August 2: Adair and Adams Counties

Following a quiet July, a cold front swept through Iowa on the afternoon of August 2. Thunderstorms erupted along the leading edge of the cold front, aided by over 6000 J/Kg of surface based CAPE. Despite the lack of low level or deep wind shear, the cold front generated enough localized spin along its forward flank to produce a very picturesque tornado just after 6:20pm when this broad circulation was stretched by a developing thunderstorm updraft in southern Adair County. With little in the way of steering winds near the surface, the tornado first drifted southwestward for about a mile, then interacted with another storm outflow boundary and turned southeast and strengthened. Widening to 300 yards, the tornado struck the hamlet of Williamson and inflicted EF1 damage to several buildings. Scouring its way southward, the tornado paused for several minutes two miles south of Williamson before turning to the northeast and dissipating. See the satellite image below that shows this unusual path of this tornado. In the 36 minutes the tornado was on the ground, it traveled only 7.5 miles.AdamsCountyTornado

Additional information on 2015 tornadoes for the state of Iowa can be found here!

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.

Spotter Training Kicks Off for 2015

Post by Brad Small – Lead Forecaster

Spotter training is underway with around 30 in-person and online talks scheduled throughout central Iowa. All spotter talks are free of charge and open to the public on a first come, first served basis. Pre-registration is not required. The training sessions are often hosted by emergency management coordinators, fire departments, or amateur radio groups. Our Advanced Spotter Training class will also be brought to northeast Iowa for the first time, taking place on the University of Northern Iowa Campus April 23.  The training will be at Latham Hall, Room 125 at 7:00 pm. Attendance at a previous basic spotter training session is recommended. A complete list of class locations and dates can be found here.

Spotters play a critical role in the warning process. Meteorologists typically consider three things when making warning decisions: 1) radar information, 2) spotter reports and 3) atmospheric conditions. The lack of spotter reports removes almost a third of the information available to the warning meteorologist. This missing piece would be similar to a doctor trying to diagnose a patient based on tests and his or her history, but not being able to talk to them and receive real-time feedback. Recent advances in technology have certainly improved our radar information, but nothing replaces actual ground-truth reports which are critical, can help people take action and save lives.

Meteorologist Rod Donavon presents spotter training in Arcadia, IA on March 16, 2015. Photo courtesy of Tom Reis.

Meteorologist Rod Donavon presents spotter training in Arcadia, IA on March 16, 2015. Photo courtesy of Tom Reis.

The National Weather Service (NWS) in Des Moines currently has over 4,400 spotters but more are still needed, especially in rural areas, as most of our spotters are clustered in cities. The need is greatest in northern and southern Iowa. Our spotters are not chasers but rather points of contact that call the NWS with severe weather reports, or are available for inquiries from NWS staff regarding conditions in their area. All participants are volunteers and are never asked to go mobile or alter their plans on any given day. Being a spotter is a great way to help your community. The report you submit may make the difference in a severe weather situation and save lives. Reports also help document past events for research and insurance purposes.

The public is encouraged to submit severe weather reports even if you have never attended a training session. The National Weather Service actively monitors Twitter and Facebook via social media. Anybody can use the #nwsdmx or #iawx hashtags to submit reports and hail or wind damage photos via Twitter (@NWSDesMoines). Similarly, Facebook (NWSDesMoines) can also be used to submit weather reports.

Additional information on the spotter program and training resources can be found here.

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:
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:,1990tornadoes

NWS Des Moines at Iowa Homeland Security Conference

Staff members from both WFO Des Moines IA and WFO Quad Cities IA/IL participated in the 11th annual Iowa Homeland Security Conference in Des Moines, Iowa, on October 21-22, 2014. They led an invited breakout session titled “National Weather Service Support Services in Times of Disaster.”

During the session Melinda Beerends (General Forecaster/WFO Des Moines) and Jeff Zogg (Senior Service Hydrologist/NWS Des Moines) discussed Decision Support Services and related tools the NWS can provide before, during and after weather-related and weather-sensitive events. In addition, they used mock scenarios to highlight the potential utility of NWS Decision Support Services and tools. They also engaged the audience to better understand the needs of NWS Emergency Management partners. The breakout session was well-attended and generated positive feedback as well as subsequent discussions between conference participants and NWS staff. Melinda and Jeff were joined by Ken Harding (MIC/WFO Des Moines), Donna Dubberke (WCM, WFO Quad Cities IA/IL) and David Cousins (Meteorologist/WFO Quad Cities IA/IL).

Melinda Beerends, General Forecaster, discusses NWS decision support resources with emergency managers.

Jeff Zogg, Senior Hydrologist, discusses NWS decision support resources with emergency managers.

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

Tornadic Debris Signatures in Iowa

Between 2011 and 2013, the National Weather Service WSR-88D Doppler radar network underwent a major upgrade to dual-polarization (dual-pol). Now, instead of sending out just one radio wave oriented in the horizontal, the radar simultaneously sends out a horizontal and vertically polarized wave. This enables the radar to take a cross-section of whatever particles it samples and assists meteorologists in determining their size, shape, and concentration. It also helps delineate which scatterers are meteorological (rain, hail, snow, etc.) or biological (birds, dust, and insects).

The dual-pol upgrade introduced three new products on top of the legacy reflectivity, velocity, and spectrum width data. The first, differential reflectivity (ZDR), simply calculates the difference between the horizontal and vertical channel reflectivity values. Positive numbers indicate objects oriented in the horizontal, negative values denote vertically oriented objects, and values near 0 signify spherical objects. The radar samples millions of particles multiple times within a single range bin, and correlation coefficient (CC) measures the similarity of these objects to one another. A value of 1 indicates uniformly shaped particles, while the closer one gets to 0, the more random the shape and size of the scatterers. Usually anything below 0.8 is non-meteorological in nature (the exception being large hail). Finally, differential phase shift (KDP) calculates the attenuation difference between the horizontal and vertical channels. Since rain drops become flattened as they fall and thus will attenuate the horizontal channel more than the corresponding vertical channel, KDP does an excellent job of locating regions of heavy rainfall.

One special phenomenon that has been observed on dual-pol radars with some tornadoes is the tornadic debris signature, or TDS. As the name implies, the radar is actually sampling the debris being lofted thousands of feet into the air by a tornado. Debris identification was possible before the implementation of dual-pol, but involved correlating a small but intense area of higher reflectivity values with a tight velocity couplet. Known then as a “debris ball”, it was difficult to determine in real-time and sampled on only a select few tornadoes. Now, the CC and ZDR products make locating a debris signature much easier. Debris will present a very low CC signal owing to their plethora of shapes and sizes. The tumbling nature of the debris will also result in a near 0 ZDR value since the objects “appear” circular to the radar beam. The colocation of the high reflectivity values, a tight velocity couplet, and low CC/ZDR values together form the text-book TDS. The stronger and closer a tornado is to a radar site, the more likely it is that the radar will display a TDS.

The Des Moines WSR-88D radar was modernized with dual-pol capabilities in September 2012.  A review of radar data for the 49 tornadoes that have been recorded in the NWS Des Moines service area (central third of Iowa) in the last two years turned up six definitive TDSs and four likely candidates whose radar characteristics did not quite fit the traditional TDS model and are still being investigated. Thus, TDSs were only found for 12% of the total number of tornadoes sampled by the radar (20% if the probable TDSs are included). All but one of these signatures were noted during the 2014 tornado season, which was significantly more active than 2013. Each TDS, like the tornadoes that produced them, was unique in its size, shape, and duration. However, many of the signatures behaved like a plume, originating from the tornado and spreading out over time.

There was little correlation between the strength/duration of the tornado and whether it produced a TDS. The Lake Panorama tornadoes of May 11, 2014 and the Zearing to Union tornado of June 30 were long-tracked tornadoes relatively close to the radar that caused substantial damage, yet failed to produce a TDS. Meanwhile, brief and weak tornadoes that hit didn’t strike any major objects produced TDSs. Four TDSs alone were sampled with just one storm system on June 30, 2014 in Adair, Madison, and Warren counties. The strongest and most persistent TDS was sampled on July 6, 2014 with a strong EF1 tornado over northern Tama County near Traer.

A prominent TDS (black circle) with a tornado north of Traer on July 6, 2014

A prominent TDS (black circle) with a tornado north of Traer on July 6, 2014

Blog post by Kevin Skow