Climate | The Weather Whisper

On This Date in Iowa Weather History – March 13, 1990

March 13, 2018March 13, 2018 by NWS Des Moines

March 13, 1990: A devastating tornado outbreak brought a total of 59 confirmed tornadoes across Oklahoma, Kansas, Nebraska, and Iowa (See Figure 1 Below). The tornado outbreak brought two F5 tornadoes and two F4 tornadoes across the central United States (See Table Below). One of the F5 tornadoes was the historic Hesston, Kansas tornado. Across Iowa, multiple severe thunderstorms swept across the state and produced at least 14 tornadoes, including an F4 which struck areas around Prairieburg and Worthington, Iowa and an F2 which injured 15 people and produced 6 million dollars in damage in and around Ankeny, Iowa. Hail reports ranged up to golf ball size near Elvira and wind gusts in excess of 75 mph were reported around Little Sioux and Logan. This was part of a wild stretch of weather in early to mid 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!

Figure 1: March 13, 1990 Tornado Outbreak.

https://www.weather.gov/oun/events-19900313

https://www.weather.gov/ict/hesston

https://www.weather.gov/gid/48406

http://www.ustornadoes.com/2012/03/13/the-march-13-1990-central-u-s-tornado-outbreak-and-two-kansas-f5s/

http://www.crh.noaa.gov/Image/ict/hesston/hesston_nws.pdf

On This Date in Iowa Weather History: Dunkerton, Iowa F3 Tornado – May 11, 2000

May 11, 2017 by NWS Des Moines

On May 11, 2000, severe thunderstorms produced large hail and at least seven tornadoes across northeastern Iowa including one that killed one person and injured 25 others as it produced F3 damage near Dunkerton, Iowa. This would be affecting some of the same areas that would be struck by the EF5 Parkersburg tornado eight years later. The largest reported hail stones were the size of baseballs, falling near Dorchester in Allamakee County.

You can find more information regarding this event from the following sources:

http://www.silverliningtours.com/may-11th-2000-dunkerton-iowa-f3-tornado/

http://cbs2iowa.com/news/local/15-years-since-dunkerton-tornado

http://wcfcourier.com/news/top_story/five-years-later-dunkerton-remembers-tornado/article_c812a6b7-5378-57f8-b14e-f312e62955d9.html

Spring and Summer Outlooks for Iowa – 2017

April 1, 2017 by NWS Des Moines

Introduction

Now that we’re finally exiting the winter months and well on our way to spring, you’re probably wondering what might be in store for the remainder of spring and summer. While seasonal forecasting is far from perfect, we can often times get a feel for what may occur based on teleconnections. What is a teleconnection you ask? Good question. In atmospheric sciences, teleconnections are anomalies that have shown a relation to each other. A great example of a teleconnection that many have heard about is El Nino, or more properly, El Nino-Southern Oscillation (ENSO). For those that have seen previous seasonal outlooks from our blog, you are probably already familiar with what ENSO is. For those that are not, take a peek below.

ENSO refers to a phenomenon that exists along the equatorial Pacific Ocean. It is categorized as El Nino or La Nina depending on the type of anomaly or Neutral if there is no anomaly or a very weak one. More specifically, El Nino is characterized by anomalously warm seas surface temperatures that propagate eastward towards the South American coast. Conversely, La Nina is characterized by anomalously cool sea surface temperatures off of the coast of South America that propagate into the central Pacific Ocean. The oscillation between the two is ENSO. Do determine whether or not El Nino or La Nina conditions exist, the Oceanic Nino Index (ONI) is used. The ONI is a measure of above and below normal sea surface temperatures within specific regions of the equatorial Pacific. For an event to be declared, 5 consecutive over-lapping 3 month periods must be anomalous one way or another by 0.5 deg C or more. El Nino would be for positive anomalies and La Nina for negative ones. Anything that does not meet the 5 consecutive period criteria or is within +/- 0.5 deg C is declared Neutral. Note the difference between conditions and event. Conditions exist during any 3 month averaging period, while an event takes the 5 consecutive over-lapping 3 month periods mentioned previously.

At this point, you may be wondering what Pacific Ocean sea surface temperatures have to do with weather in the in the United States, let alone Iowa. The atmosphere is constantly in flux, responding to various inputs such as ENSO conditions in the Equatorial Pacific in an attempt to reach equilibrium. Phenomena that last long periods of time and occur regularly can affect atmospheric conditions in ways that lead to tendencies in other areas, teleconnections. A number of phenomena across the globe have been researched and found to correlate to weather patterns in other locations across the globe, and ENSO is the most researched and well known teleconnection for the United States. We’ll proceed to take a look at the tendencies for forecasted neutral to El Nino conditions in Iowa for the upcoming Spring and Summer seasons.

For more detailed information about El Nino and La Nina, atmospheric conditions, thresholds, U.S. impacts, global impacts, and more, check out: https://www.climate.gov/enso

For more detailed information about the Oceanic Nino Index, check out: http://www.cpc.noaa.gov/products/analysis_monitoring/ensostuff/ensoyears.shtml

Spring

Currently, Neutral conditions exist within the Nino 3.4 region, having just come out of relatively weak La Nina conditions through winter. Official ENSO probabilistic forecasts indicate a likely transition towards El Nino conditions within the Nino 3.4 region as spring and summer progresses. Though focusing on Spring alone, forecasts heavily favor Neutral conditions, which makes sense in the short term considering the region just came out of La Nina conditions.

(Image 1: Official probabilistic ENSO Forecast from the Climate Prediction Center and International Research Institute for Climate and Society)

Noting the heavy lean to neutral conditions within the forecast, we will focus strictly on historical Neutral events for Iowa and surrounding areas during Spring. It should be noted that with conditions freshly coming off of a La Nina event, atmospheric response, especially as it pertains to the United States, may be in transition throughout Spring as neutral conditions set in. Historically, temperatures during Neutral conditions have leaned on the cooler side of average for the Upper Midwest and Upper Mississippi Valley’s with Iowa on the southern edge and with only minimal cool departures (Image 2: Temperature Anomalies (F) for previous Neutral events during the Spring). The analysis for precipitation points towards above average precipitation throughout much of the Mississippi Valley and Upper Midwest, including the entire state of Iowa. Once again, though, the state finds itself on the lower end of the departures (Image 3: Precipitation anomalies (in) for previous Neutral events during the Spring). For both temperature and precipitation, the largest departures are well away from Iowa, predominantly centered on the south and west.

Comparatively we’ll take a quick look at the official Climate Prediction Center (CPC) outlooks for Spring as well. As it pertains to temperatures, the CPC suggests a slightly better opportunity for above normal temperatures versus normal or below normal through Iowa (Image 4: Spring temperature outlook from the Climate Prediction Center). Looking at precipitation, the CPC indicates a slightly better opportunity for above normal precipitation over northern Iowa, while central and southern Iowa has equal chances for above, below, or normal precipitation (Image 5: Spring precipitation outlook from the Climate Prediction Center). While the CPC precipitation forecast roughly resembles a nod towards the Neutral analysis, temperatures do not. Which possibly indicates lingering La Nina influence as the atmosphere continues to respond to incoming Neutral conditions or the influence of other phenomena and atmospheric patterns being taken into consideration.

: Image 1: Official probabilistic ENSO Forecast from the Climate Prediction Center and International Research Institute for Climate and Society

: Image 2: Temperature Anomalies (F) for previous Neutral events during the Spring

: Image 3: Precipitation anomalies (in) for previous Neutral events during the Spring

: Image 4: Spring temperature outlook from the Climate Prediction Center

: Image 5: Spring precipitation outlook from the Climate Prediction Center

Summer

Now with summer a couple of months away yet, a bit more uncertainty comes into play for the ENSO forecasts. Recall the forecast at the beginning showed increasing likelihood of El Nino conditions setting in, but hovered around 40-50%, with Neutral conditions taking up much of the remaining likelihood. With that in mind, we’ll take a quick look at what both Neutral and El Nino conditions have resulted in historically.

Examining Neutral conditions first, there is no strong tendency for above or below average precipitation within the state, let alone the surrounding states (Image 6: Precipitation anomalies (in) for previous Neutral events during the Summer). Conversely temperatures do show a tendency to be above average throughout most of Iowa and much of the United States for that matter (Image 7: Temperature anomalies (F) for previous Neutral events during the Summer). The best tendencies for precipitation reside through the Appalachian region and for temperature the southwest US.

On the El Nino side of the equation, precipitation tendencies show up within the state and surrounding areas, however they are a bit of a mixed bag of both above and below average (Image 8: Precipitation anomalies (in) for previous El Nino events during the Summer). On the temperature side, history favors below average temperatures throughout Iowa and surrounding areas, which opposite that of historical Neutral conditions (Image 9: Temperature anomalies (F) for previous El Nino events during the Summer). In the El Nino case, it is hard to pinpoint the best tendency for precipitation within the United States given the mixed responses, whereas the northern Great Lakes region shows the best tendency for temperatures.

Once again to give some perspective, we’ll take a quick look at the Climate Prediction Center forecast for the summer months. At first glance, both the precipitation and temperature summer outlooks from the Climate Prediction Center loosely resemble the Neutral conditions depicted above versus the El Nino ones (Image 10: Spring precipitation outlook from the Climate Prediction Center) (Image 11: Spring temperature outlook from the Climate Prediction Center). Recall once again that the atmosphere takes time to respond to changes such as ENSO. Should El Nino make an appearance it will have to traverse through Neutral conditions first, remember we just came out of La Nina, on its way to El Nino. So void of other influences, it would make a degree of sense that the atmosphere may still be responding to Neutral conditions even if El Nino creeps in. Of course, ENSO is not the only teleconnection that influences our weather conditions. Others that have been and are continuing to be researched include the North Atlantic Oscillation, the Madden-Julien Oscillation, the Pacific Decadal Oscillation, and more. In future editions we may explore how some of these other teleconnections can affect Iowa and the United States. Until then, we will see how spring and summer play out and whether or not ENSO tendencies appear.

: Image 6: Precipitation anomalies (in) for previous Neutral events during the Summer

: Image 7: Temperature anomalies (F) for previous Neutral events during the Summer

: Image 8: Precipitation anomalies (in) for previous El Nino events during the Summer

: Image 9: Temperature anomalies (F) for previous El Nino events during the Summer

: Image 10: Spring precipitation outlook from the Climate Prediction Center

: Image 11: Spring temperature outlook from the Climate Prediction Center

Blog post by: Allan Curtis, Meteorologist Intern

On this Date in Iowa Weather History: 1959 Girl’s State Basketball Winter Storm

March 14, 2017 by NWS Des Moines

On March 14-16, 1959, a major winter storm struck Iowa as a potent low pressure center moved east northeast out of Kansas into central Illinois resulting in 6 deaths and 1 injury. Precipitation began in southern Iowa as rain on the morning of the 14^th then started to switch to a heavy wet snow by afternoon. The heaviest snowfall occurred overnight on the 14^th-15^th, with 4 inches or more falling in a wide swath from southwest to northeast across the state and some areas within that band receiving 8 to 10 inches. The highest reported storm total snowfall accumulations included 12.5 inches at New Hampton, 12.0 inches at Cresco, and 10.0 inches at Clarion, Fayette, and Fort Dodge. Winds gusting to as high as 60 mph caused severe blowing and drifting of the snow, commonly producing drifts up to 10 feet deep. There were even reports in northeastern Iowa with drifts as deep as 15 feet! Across about the southern half of the state, the heavy snow remained very wet and froze to all surfaces. As a result, thousands of trees, utility poles and lines were snapped or heavily damaged. Even after the heavy snow ended on the 15^th, frozen surfaces and high winds continued to make travel impossible across most of the state. In fact, Des Moines and Dubuque authorities prohibited any travel to or from their cities. Also in Des Moines, there were 5,000 basketball fans attending the girls state tournament that spent the night in the Veterans Memorial Stadium building.

On This Date In Iowa Weather History – 1991 Halloween Storm

October 31, 2016November 1, 2016 by NWS Des Moines

1991: A major winter storm pounded the upper Midwest from October 30^th into November 2^nd with some of the most severe effects occurring on Halloween. Snow moved into southern Iowa on the afternoon of the 30^th and changed to mixed precipitation and ice on the morning of the 31^st and continuing into late afternoon on November 1^st. Total ice accumulations ranged from 1 to 2 inches from southwest into north central Iowa and 2 to 3 inches across southern and southeast Minnesota. In northwest Iowa, the precipitation fell as all snow. Total snow accumulations of 8 inches or more blanketed the area with 15.0 inches falling at Estherville. Stong winds produced blizzard conditions into November 2^nd. The damage and hazardous travel conditions were so severe and extensive that 52 of the 99 counties in Iowa were declared disaster areas. Highways and interstates were closed across most of the state and Halloween festivities were cancelled at many locations. As the storm system moved further northeast it dumped 36.9 inches of snow at Duluth which, at the time, was the largest storm total snowfall accumulation on record in Minnesota until it was surpassed in 1994.

Extreme cold followed the crippling Halloween Storm from November 4-8, 1991. With the fresh snow pack in place, on November 4^th nearly every reporting station in the state fell into the single digits and remarkably some western stations reported their earliest subzero temperatures on record, including Sioux City where the low was -3°F. Des Moines and Waterloo both established daily records with a low of 4°F. The lowest temperatures reported on the morning of the 4^th included -7°F at Sioux Rapids, -9°F at Hawarden, -10°F at Sheldon, and -11°F at Cherokee. Amazingly, even colder weather would settle across Iowa a few days later with nearly the entire state falling below zero on the mornings of November 7^th and 8^th. On the 7^th many stations set daily record lows and at numerous locations this is the earliest date on record on which the temperature has fallen below zero, including at Des Moines where the low was -3°F. The lowest reported temperatures in Iowa that morning included -12°F at Audubon, -13°F at Perry, -14°F at Le Mars, -15°F at Sheldon, -16°F at Guthrie Center, -17°F at Cherokee, and -19°F at Hawarden. On the morning of the 8^th reported low temperatures included -2°F at Burlington, -8°F at Bedford and Grinnell, -11°F at Sac City, -12°F at Atlantic and Le Mars, -13°F at Cherokee and Perry, and -14°F at Guthrie Center.

: Regional map of the the Halloween 1991 winter storm.

: Accumulated Snowfall across Iowa from October 30 to November 2, 1991. The bulk of the precipitation fell on Halloween 1991 much of the eastern two-thirds of the state receiving freezing rain.

: Regional map of the bitter cold temperatures on November 7, 1991.

: Bitter cold temperatures followed the Halloween Winter Storm with the coldest day occurring on November 7, 1991.

On this Date in Iowa Weather History – 1997

October 26, 2016October 26, 2016 by NWS Des Moines

October 25-26, 1997

A major winter storm moved into western Iowa just before midnight on October 25^th and spread across about the southeastern two thirds of the state on the 26^th. Two bands of heavy snow developed, one extending from Council Bluffs northeast through Boone and the other extending from northern Ringgold County northeast to around Cedar Rapids. The heaviest snowfall accumulations included 11.3 inches at Knoxville and an amazing 13.0 inches southwest of Mineola in Pottawattamie County. Electricity was lost to tens of thousands of homes and businesses in central and southern Iowa as snow laden trees fell onto power lines. This was the most significant heavy snow so early in the season in Iowa since the storm of October 16-17, 1898. On the morning of the 27^th temperatures plummeted, with the aid of the fresh snow pack on the ground, bottoming out at 9 F at Atlantic and Guthrie Center which was the coldest Iowa temperature recorded so early in the season since 1972. While this system produced nearly all of the snow that fell during the month of October 1997, it was still enough to make it the third-snowiest October on record in Iowa only behind those of 1898 and 1925.

: Total snowfall accumulation from a major winter storm that occurred on October 25-26, 1997.

: Average Minimum Temperature on the morning of October 27, 1997 after a major winter storm.

Fall and Winter Outlooks for Iowa

August 5, 2016 by NWS Des Moines

Introduction

The talk all winter and spring was El Niño and how it would affect large portions of the United States. As spring ended and summer took over, El Niño conversations were quickly replaced with La Niña thoughts as conditions began to transition. Taking a step back, for those that are unfamiliar with the terms El Niño or La Niña, they are phenomena that exist along the equatorial Pacific Ocean. An El Niño event is characterized by anomalously warm sea surface temperatures that propagate eastward towards the South American coast. Conversely, a La Niña event is characterized by anomalously cool sea surface temperatures off the coast of South America that propagate into the central Pacific Ocean. The oscillation between the two is called the El Niño-Southern Oscillation (ENSO). For an event to be categorized as an El Niño or La Niña, the Oceanic Niño Index (ONI) is used. The ONI is a measure of above and below normal sea surface temperatures within a specific region of the equatorial Pacific. Anomalous values of 0.5 C or greater for 5 consecutive over-lapping seasons would be an El Niño. Conversely, values of -0.5 C or less for 5 consecutive over-lapping seasons would be a La Niña. In between 0.5 C and -0.5 C or for periods that do not meet the 5 consecutive over-lapping seasons, would be categorized as neutral.

At this point, you may be wondering what Pacific Ocean sea surface temperatures have to do with weather in the United States, let alone Iowa. The atmosphere is constantly in flux, responding to various inputs such as El Niño or La Niña conditions in the Equatorial Pacific, in an attempt to reach equilibrium. Phenomena that last long periods of time and occur regularly can affect atmospheric conditions in ways that lead to tendencies in other areas, known as teleconnections. A number of phenomena across the globe have been researched and found to correlate to weather patterns in other locations across the globe, and El Niño and La Niña are probably the most researched and well known teleconnections. We’ll proceed to take a look at the tendencies in Iowa during neutral and La Niña conditions and how they compare to the current seasonal outlooks from the Climate Prediction Center.

For more detailed information about El Niño and La Niña, atmospheric conditions, thresholds, U.S. impacts, global impacts, and more, check out: https://www.climate.gov/enso

For more detailed information about the Oceanic Niño Index, check out: http://www.cpc.noaa.gov/products/analysis_monitoring/ensostuff/ensoyears.shtml

Fall

As hinted at above, El Niño conditions existed through the winter and spring months, but weakened into summer and are forecast to continue into at least neutral conditions and possibly transition into La Niña conditions through the fall months (Image 1).

Image 1: Official probabilistic ENSO Forecast from the Climate Prediction Center and International Research Institute for Climate and Society.

First, focusing on neutral conditions, when looking at previous historical neutral events that occurred during the fall months, temperatures have a tendency to be cooler throughout the state (Image 2). On the other hand, precipitation does not have a strong tendency state wide, and instead is a mixed bag, indicating a weaker correlation (Image 3).

Should La Niña conditions set in, once again the strongest tendency is seen in temperatures, however this time it is for warmer temperatures throughout the state (Image 4). Then similarly to neutral, precipitation does not show a strong tendency, but does lean toward slightly drier conditions (Image 5).

While all of that is well and good, how does all of it compare with the Climate Prediction Center’s (CPC) official fall outlook? For their most recent fall outlook, temperatures nationwide show an increased chance for above normal temperatures (Image 6). The precipitation outlook shows no tendency for above or below normal precipitation for much of the United States, including Iowa (Image 7). When comparing to the neutral and La Niña tendencies above, the outlooks do not closely resemble either, possibly indicating low confidence or another teleconnection playing a significant role.

Image 2: Temperature Anomalies (F) for previous Neutral events during the Fall.

Image 3: Precipitation anomalies (in) for previous Neutral events during the Fall.

Image 4: Temperature anomalies (F) for previous La Niña events during the Fall.

Image 5: Precipitation anomalies (in) for previous La Niña events during the Fall.

Image 6: Fall temperature outlook from the Climate Prediction Center.

Image 7: Fall precipitation outlook from the Climate Prediction Center.

Winter

Shifting towards winter, forecasts show a likely probability of La Niña conditions setting in and that’s what we will focus on here. La Niña has a pretty strong signal across the United States, however Iowa is caught in the transition zone of above normal temperatures to the south and below normal temperatures to the north (Image 8). Precipitation, also has a decent signal across the United States, but once again Iowa does not fall within an area of anomalies one way or another (Image 9). Instead, the best signals are found through the Ohio River valley, Pacific Northwest, the Southeast, and California.

When compared to the CPC outlook for winter, striking resemblances are immediately seen. The strongest resemblance is seen within temperatures, where the CPC highlights the Southeast and South for above normal temperatures and the North for below normal temperatures (Image 10). Strong resemblances are also seen in the CPC outlook for precipitation, where the Ohio River Valley and Pacific Northwest are highlighted for above normal precipitation, and the Southeast, South, and California for below normal precipitation (Image 11). Unfortunately for Iowa, with the seeming strong tendency for the CPC outlooks to lean towards La Niña conditions this winter, the CPC does not depict strong feelings one way or the other for precipitation or temperatures.

: Image 8: Temperature anomalies (F) for previous La Niña events during the Winter.

: Image 9: Precipitation anomalies (in) for previous La Niña events during the Winter.

: Image 10: Winter temperature outlook from the Climate Prediction Center.

: Image 11: Winter precipitation outlook from the Climate Prediction Center.

Blog post by Allan Curtis, Meteorologist Intern, NWS Des Moines

Iowa Monthly Climate Summary – July 2016

August 5, 2016 by NWS Des Moines

Temperatures

The statewide average temperature for July 2016 was 73.0°F which was 0.6°F below normal (See Figure 1). July 2016 ranks as the 50^th coolest July on record out of 144 years of statewide climatic records. The monthly average temperature at Des Moines was 76.8°F or 0.5°F above normal with the highest temperature coming in at 97°F on the 21^st and lowest temperature at 58°F on the 1^st. Waterloo’s monthly average temperature was 72.8°F or 0.8°F below normal. The highest temperature in Waterloo for the month of July was 93°F on the 21^st and 52°F on the 3^rd.

Through the 4^th of July weekend, cooler than normal temperatures prevailed across the state (See Figure 2). In fact, a few locations recorded low temperatures in the 40s on the morning of the 3^rd (See Figure 3). Estherville, Elkader, and Cresco all had low temperatures at 47°F on July 3^rd. Then the hot and humid conditions developed and dominated throughout much of the remainder of the month. There were a few days peppered into the last 3 weeks of the month when cloud cover and thunderstorms kept temperatures below normal. Regardless, the hottest stretch occurred from the 17^th to the 27^th. The hottest temperature of the month throughout the entire state was 97°F on the 20^th at Sioux City and at Des Moines and Lamoni on the 21^st. Much of the state had heat index readings well over 100°F between the 20^th and 23^rd (See Figures 4 & 5) due to the high humidity and dew points.

Precipitation

The monthly statewide precipitation total for Iowa during the month of July 2016 was 6.13 inches (See Figure 6). This was 1.63 inches above normal, resulting in the 16^th wettest July on record among 144 years of statewide climatic records. Des Moines totaled 6.98 inches for the month, with the bulk of that total occurring on the 19^th when 3.53 inches of rain fell. This daily total nearly doubled its monthly total up to that point. In fact, only 0.02 inches of additional rainfall accumulated the remainder of the month, but Des Moines was still 2.51 inches above normal for the entire month. Waterloo had a different outcome with 4.01 inches or 0.90 inches below normal for July.

After a dry first five days of the month, an active weather pattern developed and brought a multitude of precipitation through the 20^th. The statewide average from July 6^th to the 20^th was 4.86 inches or 2.63 inches above normal during that stretch (See Figure 7 & 8). The heaviest rainfall occurred from the southwest to north central to northeast portions of the state. Enough rain fell over central and southern Iowa to relieve some of the drought conditions except for a small area in far south central Iowa (See Figure 9).