July 2014 Central Iowa Monthly Climate Summary

Temperatures

Figure 1: Average Temperature for the month of July 2014 was 69.0°F for the entire state, while the DMX CWA was 68.8°F

Figure 1: Average Temperature for the month of July 2014 was 69.0°F for the entire state, while the DMX CWA was 68.8°F. The DMX CWA is outlined in white.

For the state of Iowa, the average temperature was 69.0°F which was 4.6°F below normal for the month of July (See Figure 1).  July 2014 is now the 5th coolest July on record for the state among the 142 years of records.* The average temperature for the Des Moines County Warning Area (CWA) was 68.8°F with the coldest spots located over the west-central and far southeast portions of the CWA (See Figure 2).

Figure 2: Average Temperature Departure from Mean for the month of July 2014 was 4°F to 5°F below normal for the month.

Figure 2: Average Temperature Departure from Mean for the month of July 2014 was 4°F to 5°F below normal for the month. The DMX CWA is outlined in white.

There were a few individual days that rose above normal, but no extended heat wave occurred during the month.  The hottest days of the month were on the 12th, 21st, 22nd, and 25th when several locations rose into the lower 90s (See Figure 3).  The hottest temperature of the month, within the Des Moines CWA, was 95°F at Osceola on the 22nd. The highest temperature throughout the entire state was 102°F on the 25th at Sidney in far southwest Iowa. Des Moines reached at least 90°F only 3 times during the month and normally averages 10 days with 90°F or greater during the month of July.  In similar fashion, Waterloo only had 1 day that topped 90°F but normally averages around 8 days with maximum temperatures reaching 90°F or higher in July.  Mason City continued its streak of not reaching 90°F in July as the highest temperature at the station was 89°F.  By the end of the month, this streak extended to 325 days since the last time the station reached 90°F on September 9, 2013.

Figure 3: Average Maximum Temperatures for July 21-22, 2014. These were a couple of the hottest days of the month across central Iowa.

Figure 3: Average Maximum Temperatures for July 21-22, 2014. These were a couple of the hottest days of the month across central Iowa.

On the flip side, there were many more colder than normal days in July.  Table 1 illustrates how often central Iowa was below normal during the month. Ottumwa set a couple of new daily temperature records. The first was a daily low maximum temperature of 65°F on the 2nd which broke the previous record of 67°F set back in 1944. The second record was a record low of 49°F set on the 16th breaking the previous record of 51°F in 1930.  Lamoni also set a new record low temperature of 52°F on the 16th, breaking the previous record of 55°F set in 1961. Another record low maximum of 66°F was set at Waterloo on the 2nd breaking the old record of 67°F from 1941.

Table 1: Automated Surface Observation Stations (ASOS) across central Iowa were well below normal for a good portion of the month of July 2014.

 

Precipitation

Figure 4: the accumulated precipitation percent of mean for the month of July 2014. Much of the state was well below normal, except for the southeast.

Figure 4: the accumulated precipitation percent of mean for the month of July 2014. Much of the state was well below normal, except for the southeast. DMX CWA outlined in white.

Little precipitation fell during the month of July 2014 across central Iowa and there was only one major severe weather event and that occurred on July 6. Other than southeast Iowa, the remainder of the state was well below normal for precipitation (See Figure 4). The majority of the precipitation only fell on a handful of days which includes the 5th, 6th, 12th and the 25th. The Des Moines International Airport recorded 1.99” on the 5th, while several other locations recorded at least an inch of rain on the same day (See Figure 5).  The highest precipitation total during the month, for the state and DMX CWA, was in Montezuma in Poweshiek County with a monthly total of 10.21 inches. The lowest monthly total for the state also occurred in the DMX CWA and that was 0.71 inches at Atlantic in Cass County.

A total of 9 tornadoes occurred on July 6, 2014, 8 dropped down in the DMX CWA. There were two tornadoes rated EF1 and they occurred near the towns of Reinbeck and Dinsdale. The rest were EF0 tornadoes and you can find more information about the event as well as all the tornadoes from 2014 our Tornado Page.

Figure 5: Q3 radar estimated precipitation for July 5, 2014.

Figure 5: Q3 radar estimated precipitation for July 5, 2014. http://nmq.ou.edu/

Reservoir Information

Figure 6: Saylorville Lake Reservoir pool height trend graph during the month of July 2014.

Figure 6: Saylorville Lake Reservoir pool height trend graph during the month of July 2014.

The Saylorville Reservoir pool height rose a about 7 feet during the first week of July to 877.57 feet on the 6th before gradually falling throughout the rest of the month to 851.50 feet on the 31st (See Figure 6). The maximum pool height corresponded to a maximum storage of 446,670 Acre-feet on the 6th while the lowest storage of the month was 171,070 Acre-feet on the 31st. The Des Moines River downstream of Saylorville Lake maximum stage height was 14.29 feet on the 7th and the lowest was 8.45 feet on the 31st. The maximum outflow at the same location was 19,500 CFS on the 2nd to a minimum of 5,600 CFS on the 31st.

Figure 7: The Lake Red Rock Reservoir pool height trend graph during the month of July 2014.

Figure 7: The Lake Red Rock Reservoir pool height trend graph during the month of July 2014.

Lake Red Rock Reservoir pool height rose from 755 feet on the 1st to 766 feet during the middle of the month before dropping back to around 757 feet by the 31st (See Figure 7).  The pool storage nearly reached 1,000,000 Acre-feet when it maxed out at 910,820 Acre-feet on the 11th.  The lowest storage was 483,840 Acre-feet on the 1st. The stage height of the Des Moines River downstream of Lake Red Rock Reservoir ranged from 90.37 feet on the 2nd to 93.69 feet on the 13th.  It remained above 93 feet from the 1th to the 28th and it was only below 91 feet the first two days of the month.  The outflow from Lake Red Rock increased from 13000 CFS on the 1st to around 22,000 CFS by the 12th where it remained steady until the 29th when it dipped down to 18,400 CFS.

*Statewide averages courtesy of State Climatologist Harry Hillaker: http://www.iowaagriculture.gov/climatology/weatherSummaries/2014/pms201407.pdf

 Blog post by Kenny Podrazik – NWS  Des Moines

June 2014 Central Iowa Monthly Climate Summary

Temperature Overview

The statewide monthly average temperature for Iowa in June 2014 was 70.3°F which was 0.6°F above normal. June 2014 ranks 55th warmest June among 141 years of records in the state of Iowa. The average temperature within the NWS Des Moines County Warning Area (DMX CWA) was 70.0°F for June 2014 and the average maximum temperature was 79.8°F and the average minimum temperature was 60.1°F. The DMX CWA is outlined in white in Figures 1-4.  Roughly 3 out the 4 weeks in June remained above normal with a cold stretch occurring from June 7 to 13 (See Figure 1).

The coldest temperature across the DMX CWA was 39°F in Emmetsburg on June 9th while the lowest in the state was 38°F at Battle Creek on the 13th. However, much of the departure from normal only ranged about 1 to 5 degrees above normal during the month. In fact, only one day topped 10 degrees above normal, within the DMX CWA, and that occurred on the 1st (See Figure 2). Since no long duration heat wave developed during June, the majority of stations only reach 90°F a couple of times. Des Moines reached exactly 90°F on the 16th, 18th, and 20th while Waterloo’s hottest temperature was only 88°F on the 1st. Typically, Des Moines averages 4.5 days and Waterloo averages 4.1 days with 90°F or greater maximum temperatures during the month of June. The two stations combined for 4. Other ASOS (Automated Surface Observing System) stations such as Lamoni, Ottumwa, Marshalltown, and Mason City never topped 90°F during the month. By the end of the month, Mason City still had not reached 90°F since September 9, 2013 and this streak continued into July.

June7-13-AVG TempDFM

Figure 1: Average Temperature Departure from Mean from June 7 to June 13, 2014. The map shows much of the state well below normal.

June1-AVG TempDFM

Figure 2: Average Temperature Departure from Mean on June 1, 2014.

Precipitation Overview

The statewide monthly average precipitation for June 2014 was 9.94 inches which was a whopping 4.92 inches above normal (See Figures 3 and 4).  June 2014 became the 3rd wettest June among 141 years of records and the 4th overall wettest month for Iowa (See Table 1).

June 2014 Monthly (Top 4) Precipitation Records for the entire state of Iowa. 2014 comes in at number 4th overall.

Table 1: The Top 4 Monthly Precipitation Records for the entire state of Iowa. June 2014 comes in at number 4th overall for all months.

Daily precipitation records were set at Mason City, Lamoni, and Waterloo during the month (See Table 2). Waterloo, Iowa had its 3rd highest June precipitation with a total of 9.63” for the month, which was just ahead of the 8.79” total in 2008 (See Figure 5).  Most sites across central Iowa reported precipitation for at least two weeks (not consecutively) out of the month of June. For instance, Ottumwa recorded at least a trace of precipitation 19 out of the 30 days in June and 6 days had at least a half inch or more. Des Moines, Waterloo, Lamoni, Estherville, and Marshalltown all had 4 days with 1” or more of precipitation. Ames came in with 5 days with daily totals of 1” or more. All this precipitation led to significant flooding and flash flooding across the DMX CWA during June 2014. The upper Des Moines River and the Cedar River were affected the most as 13 river stations topped flood stage.

A very active severe weather pattern occurred in Iowa during June 2014 with June 3, June 16, and June 30 receiving the most significant and widespread severe weather. On June 16, 9 tornadoes occurred within the DMX CWA, while altogether there were 12 tornadoes in the state. June 29-30, separate systems, but the two-day total for tornadoes was 13 for the state, in which 11 occurred in the DMX CWA. For the entire month, there were 31 tornadoes across the state of Iowa resulting in a total path length of over 107 miles long. The highest rating was EF2 for two tornadoes. The first one occurred on June 3 in Pottawattamie County southeast of Bentley and the second dropped across Tama County northwest of Traer. For more detailed Iowa tornado information, visit our tornado page: http://www.crh.noaa.gov/dmx/?n=iators2014

Tornadoes were not the only severe weather hazards that affected Iowa in June as the aforementioned dates, along with a few other events, produced significant damage from very large hail and damaging winds. On June 3, southwest Iowa was hardest hit with wind-driven hail as it produced significant damage to crops and buildings, where siding was completely shredded off several homes (See Figure 6). June 30 produced similar wind-driven hail that caused major damage across portions of central Iowa and more detailed information the event can be found here: http://www.crh.noaa.gov/dmx/?n=june30event

DailyPrecipRecords-June2014

Figure 3: Statewide Accumulated Precipitation: Percent of Mean for the month of June 2014

Figure 3: Statewide Accumulated Precipitation: Percent of Mean for the month of June 2014

Figure 4: Accumulated precipitation for June 2014.

Figure 4: Accumulated precipitation for June 2014.

Figure 3: Waterloo Accumulated Precipitation for June 2014 as well as June 1947, 1993, and 2008.

Figure 5: Waterloo Accumulated Precipitation for June 2014 as well as June 1947, 1993, and 2008.

Figure 4: Significant wind-driven hail event occurred on June 3, 2014. This image from a resident in Treynor, IA had major damage to the siding and roof.

Figure 6: Significant wind-driven hail event occurred on June 3, 2014. This image from a resident in Treynor, IA had major damage to the siding and roof. Image courtesy of KWWL.

Reservoir Information

The Saylorville Reservoir pool height began at 837.84 feet on the 1st and rose over 30 feet to a height of 868.23 feet by the 30th (See Figure 7). The normal pool height is 836 feet. The pool storage monthly maximum was 333,960 Acre-feet on the 30th while the minimum pool storage was 67,068 Acre-feet on the 13th. The Des Moines River downstream of Saylorville Lake fluctuated throughout the month before cresting at 15.25 feet on the 27th with a flow of 19,500 cubic feet per second or CFS (See Figure 8).

Lake Red Rock Reservoir pool height increased from 743.77 feet on the 1st to 752.30 feet by the 30th. The pool storage doubled in volume within two weeks as it rose from a minimum of 189,420 Acre-feet on the 15th to a monthly maximum of 404,370 Acre-feet on the 30th (See Figure 9). The stage height of the Des Moines River downstream of Lake Red Rock Reservoir increased from a low of 86.73 feet on the 1st to a maximum height of 92.50 feet on the 29th.  The outflow maxed out at 19,000 CFS on the 28th and 29th while the lowest flow was 3,950 CFS on the 16th.

June2014SaylorvillePoolHeight

Figure 7: Stage height trend graph for Saylorville Lake in June 2014.

DSMRiver-Downstream-June-CFS

Figure 8: Output, measured in cubic feet per second, along the Des Moines River downstream of Saylorville Lake Reservoir.

RedRock Pool Storage-June 2014

Figure 9: The storage trend for June 2014 at Lake Red Rock Reservoir.

References:

http://mrcc.isws.illinois.edu/
http://xmacis.rcc-acis.org/
http://www.iowaagriculture.gov/climatology/historicWeatherReports.asp
http://rivergages.mvr.usace.army.mil/WaterControl/new/layout.cfm
http://mesonet.agron.iastate.edu/

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.

BakerinkPrussiaIATornado

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.

August10_1939_LargeSurfaceMap-1230z-resize

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

August10_1939_SurfaceMap-1230z-resize

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

19390810-resize

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%

References:

http://www.thepeoplehistory.com/1939.html
http://en.wikipedia.org/wiki/Main_Page
http://mlb.mlb.com/mlb/standings/index.jsp?tcid=mm_mlb_standings
http://www.history.com/topics/world-war-ii
http://www.usinflationcalculator.com/
http://www.census.gov/construction/nrs/pdf/newressales.pdf

Blog post by Kenny Podrazik – NWS Des Moines

Snow in September?

Believe it or not, there have been at least nine years in which snow has been recorded in Iowa in the month of September, most recently in 1995, as detailed in Table 1 at the end of this document. The most remarkable of these events is the very early snowfall of September 16, 1881, which was amazing not only for its earliness in the season but also for the extent and amount of snowfall. The track of the surface low pressure center associated with this storm system is illustrated in Figure 1, a reprint of the original “War Department Weather Map” from September of 1881. At the time weather observations and reports were filed by the U.S. Army Signal Service, the progenitor of the modern National Weather Service. In the report of the Chief Signal Officer for that month, the development of the low pressure center is detailed as follows:

“This storm, which pursued a very anomalous track, was first evident in Texas, where on the 14th it moved in a track nearly due east. At the midnight observation, while the storm center was near New Orleans, a barometric depression extended from the Gulf of Mexico to the Lake Superior region. At the same time [an area of high pressure] prevailed with fair weather in New England. These conditions were unfavorable to an eastern progress of the storm, and on the 15th the depression moved in a northerly course to Lake Michigan. On the 16th, with diminishing energy, the storm center moved into Iowa and Minnesota, and on the 17th into Manitoba. The track on the 16th and 17th is very remarkable, and probably for a storm of such energy will have no parallel in the history of the Signal Service.”

Figure 1: Highlighted track of the low pressure center from September 14-17, 1881.

Figure 1: Highlighted track of the low pressure center from September 14-17, 1881.

On September 14, as the low moved across the Gulf of Mexico, fair weather prevailed across most of Iowa until a cold front moved through late in the day. At Des Moines the high temperature was 80 degrees but then the official observer wrote that, “Low stratus clouds moved rapidly from north and northwest during the afternoon and evening.” On the 15th, as the low pressure center moved northward toward Chicago, it pulled down unseasonably cool air behind the front into Iowa and spread a cold rain across much of the upper Midwest. At Des Moines the temperature fell through the day, with a high of 58 degrees measured early in the morning. The observer noted, “Cloudy and threatening weather prevailed during the day, low stratus clouds moved from the north.”

By the morning of September 16, the low pressure center was moving slowly westward into southern Minnesota and northern Iowa, pushing cold air even further southward into the central U.S. Frost was noted as far south as Arkansas and Texas and at Fort Gibson, Oklahoma ice formed on standing water. Across eastern Nebraska, southern Minnesota, and about the northwestern two thirds of Iowa the colder air allowed rain to mix with or change entirely over to snow at times, mostly in the morning. At Des Moines the high temperature for the day was only 46 degrees and the observer recorded that, “Few flakes of snow was observed.” Further north and west the snow was heavier, in some areas melting as it fell but in others managing to accumulate for a short time. At Algona an estimated 4 inches of snow fell in the morning, breaking some tree branches, but all melted by noon. The snow was observed as “quite heavy” at Creston, while “several inches” were noted between Des Moines and Atlantic and 4-6 inches were estimated on the Rock Island Railroad between Stuart and Avoca.

This stands as one of only two occasions on which fairly widespread, measurable snow has fallen in Iowa in the month of September, the other being on September 25, 1942. In that storm most of the state received snow with amounts ranging up to 4 inches at Allison, Forest City, Mason City, and Millerton and scattered tree and utility line damage noted across the state.

Table 1: Years in which snow has been recorded in Iowa in September.
1881 – widespread measurable snowfall on the 16th (see above)
1895 – “first snowflakes” noted at Madrid on the 28th
1912 – “few flakes” observed at Storm Lake and Marshalltown on the 17th and 18th
1938 – flurries reported at Orleans and Maquoketa on the 18th and 19th
1939 – traces of light snow and sleet across northern IA, 0.1” at Sheldon and 0.2” at Sibley, on the 29th and 30th
1942 – widespread measurable snowfall on the 25th (see above)
1961 – light snow across northwestern half of IA on the 30th, a few measurable amounts ranging up to 3.0” at Swea City
1985 – a few flakes at Des Moines on the 24th, widespread wintry mix with 0.5” at Audubon and Storm Lake on the 29th and 30th
1995 – a few flakes and ice pellets mixed with rain across northern IA on the 22nd

Blog post by Jim Lee

 

May 2014 Central Iowa Temperature and Precipitation Overview

This temperatures and precipitation summary covers the NWS Des Moines County Warning Area (CWA) during the month of May 2014.  The statewide climate statistics mentioned in this blog are courtesy of State Climatologist Harry J. Hillaker.  You can find a more detailed statewide monthly climate summary here: May 2014 Iowa Statewide Climate Summary

Temperature Overview

The statewide average temperature for Iowa was 61.0°F during the month of May 2014 which was normal (See Figure 1). This month ranks as the 66th warmest May on record among 142 years of records.  A roller coaster ride of temperatures affected the first half of the month before temperatures began to level out some after the 20th (See Figures 2 and 3).  For the state, temperatures remained cooler than normal the first 5 days of May where several areas in north-central Iowa dipped into the 30s for low temperatures on the mornings of May 2nd and 3rd. Another cold spell occurred on the 16th and 17th when several locations in central Iowa had light frost or even a brief freeze each morning. The coldest temperature in the Des Moines CWA was 29°F at Mount Ayr and Atlantic on the 16th and at Guthrie Center, Audubon, and Atlantic on the 17th.  However, the coldest temperature in Iowa occurred on the 16th at Spencer with a low of 24°F.  There was a brief warmup on the 7th of May across the CWA when most maximum temperatures reached the upper 80s to the lower 90s. Atlantic recorded the hottest temperature in the Des Moines CWA on May 7th with a high of 94°F. Des Moines and Lamoni reached 90°F for the first time in 2014. Temperatures cooled down considerably during the middle of the month with the coldest stretch occurring from May 13th to May 18th. The average temperatures and average minimum temperatures across the CWA ranged from 10°F to 13°F below normal (See Figures 4 and 5). Several places even dropped below the freezing mark or well into the 30s on the mornings of the 16th and 17th (See Figures 6 and 7). The last third of the month, temperatures rebounded with a long stretch of highs near or slightly above normal (See Figure 8).

Precipitation Review

Although it was an active month for severe weather and rainfall across central Iowa, the statewide average precipitation still was 1.40 inches below normal. The statewide average for the month of the May was 3.16 inches (See Figure 9) and puts May 2014 42nd driest May among 142 years of records. However, there was enough widespread rain across the state to help mitigate the drought conditions, particularly over the south and west (See Figures 10a and 10b). The most significant event during the month of May occurred on the evening of the 11th into the overnight hours on May 12.  Several locations reported over 2 inches of rain (See Figure 11).  Eight tornadoes dropped down on May 11, mainly during the late evening hours over central Iowa just west of the Des Moines Metro. EF2 damage occurred over Lake Panorama in Guthrie County around 10 p.m. CDT May 11 while several locations were affected by damaging winds. A handful over additional severe weather events transpired in May, but were isolated large hail and damaging wind events and not as widespread severe as May 11th.  On May 20th, heavy rain and large hail affected Ames, Iowa where several locations in town had significant flooding issues from 2 to 3 inches in a short time frame (See Figure 12). In fact, the Ames ASOS recorded 3.01 inches for the day which helped push the station to being above normal for the month (See Table 1). However, even though most other stations across central Iowa were above normal for precipitation by the middle of the month, the dry period during latter half led to many stations ending up with below normal precipitation for May 2014 (See Figure 13).

Reservoir Information

The Saylorville Reservoir pool height rose from 836.73 feet on the 1st to 838.10 feet by the 31st. Normal pool height is 836 feet, so the pool height barely rose 2 feet above normal during May 2014. The pool storage monthly maximum was 81,156 Acre-feet on the 16th while the minimum pool storage was 67,416 Acre-feet. The Des Moines River downstream of Saylorville Lake maximum stage height was 7.78 feet on the 17th and the lowest was 3.95 feet on the 9th. The flow at the Des Moines River downstream of Saylorville Lake increased from 1820 CFS on the 1st to 5640 CFS on the 17th before dropping back down to 1410 CFS by the 31st.

 Lake Red Rock Reservoir pool height showed very little changed during the month of May as it ranged around the normal pool height of 742 feet. The pool storage ranged from a minimum of 189,730 Acre-feet on the 2nd to a maximum of 214,750 Acre-feet on the 30th. The stage height of the Des Moines River downstream of Lake Red Rock Reservoir fluctuated from a low of 86.39 feet on the 3rd to a maximum height of 90.98 feet on the 16th.  Similarly, there was a low outflow of 1920 CFS on the 11th to a high outflow of 14,500 CFS on the 16th.

Figure 1: Statewide average temperature departure from normal during May 2014. Image is courtesy of MRCC.

Figure 1: Statewide average temperature departure from normal during May 2014. Image is courtesy of MRCC.

Figure 2: Daily Temperature Trend for Des Moines International Airport for the month of May 2014. The temperature trend during the first half of the month shows sharp contrasts before leveling out by the end of the month.

Figure 2: Daily Temperature Trend for Des Moines International Airport for the month of May 2014. The temperature trend during the first half of the month shows sharp contrasts before leveling out by the end of the month.

Figure 3: Daily Temperature Trend at Waterloo, Iowa during the month of May 2014. The temperature trend during the first half of the month shows sharp contrasts before leveling out by the end of the month.

Figure 3: Daily Temperature Trend at Waterloo, Iowa during the month of May 2014. The temperature trend during the first half of the month shows sharp contrasts before leveling out by the end of the month.

Figure 4: The Average Temperature Departure from Mean from May 13 to May 18, 2014. Much of the DMX CWA (white line) was 10 degrees or more below normal.

Figure 4: The Average Temperature Departure from Mean from May 13 to May 18, 2014. Much of the DMX CWA (white line) was 10 degrees or more below normal.

Figure 5: The Average Minimum Temperature departure from Mean from May 13 to May 18, 2014.

Figure 5: The Average Minimum Temperature departure from Mean from May 13 to May 18, 2014.

Figure 6: Surface temperatures at 7 a.m. CDT on the morning of May 16, 2014 where it shows much of central to western Iowa in the 30s. Image Courtesy of IEM.

Figure 6: Surface temperatures at 7 a.m. CDT on the morning of May 16, 2014 where it shows much of central to western Iowa in the 30s. Image Courtesy of IEM.

Figure 7: Surface temperatures at 7 a.m. CDT on May 17, 2014 where most of the state dropped well into the 30s for minimum temperatures. Image Courtesy of  IEM.

Figure 7: Surface temperatures at 7 a.m. CDT on May 17, 2014 where most of the state dropped well into the 30s for minimum temperatures. Image Courtesy of IEM.

Figure 8: The last 12 days temperatures warmed to above normal when highs rose well into the 80s over the last week of May 2014.

Figure 8: The last 12 days temperatures warmed to above normal when highs rose well into the 80s over the last week of May 2014.

Figure 9: The observed precipitation across Iowa for May 2014. The highest rainfall totals were located over west-central to south-central Iowa.

Figure 9: The observed precipitation across Iowa for May 2014. The highest rainfall totals were located over west-central to south-central Iowa.

Figure 10: The U.S. Drought Monitor shows drought conditions had improved towards the end of May (right image). The greatest chance was over south-central and west-central Iowa where the heaviest rainfall accumulated.

Figure 10a: The U.S. Drought Monitor issued on April 28, 2014 shows significant drought conditions over western and portions of southern Iowa at the beginning of May.

Figure 10: The U.S. Drought Monitor shows drought conditions had improved towards the end of May (right image). The greatest chance was over south-central and west-central Iowa where the heaviest rainfall accumulated.

Figure 10b: The U.S. Drought Monitor issued on June 3, 2014 shows drought conditions had improved towards the end of May. The greatest chance was over south-central and west-central Iowa where the heaviest rainfall accumulated.

Figure 11: NMQ Q3 Estimated 24 hour precipitation accumulation ending at 18z on May 12, 2014. Several locations received 2 to 3 inches over a good portion of the Des Moines CWA.

Figure 11: NMQ Q3 Estimated 24 hour precipitation accumulation ending at 18z on May 12, 2014. Several locations received 2 to 3 inches over a good portion of the Des Moines CWA.

Figure 12: NMQ Q3 Total precipitation estimated 1 to 3 inches over portions of central Iowa on May 20, 2014. Ames recorded just over 3 inches from the heavy rain event. The U.S. Drought Monitor shows drought conditions had improved towards the end of May (right image). The greatest chance was over south-central and west-central Iowa where the heaviest rainfall accumulated.

Figure 12: NMQ Q3 Total precipitation estimated 1 to 3 inches over portions of central Iowa on May 20, 2014. Ames recorded just over 3 inches from the heavy rain event. The U.S. Drought Monitor shows drought conditions had improved towards the end of May (right image). The greatest chance was over south-central and west-central Iowa where the heaviest rainfall accumulated.

Figure 13: Precipitation trend for the month of May at Ottumwa shows the bulk of the rain fell on May 11 before an extended dry period towards the end of the month. The majority of central Iowa reporting stations’ precipitation trend graphs were similar to this one.

Figure 13: Precipitation trend for the month of May at Ottumwa shows the bulk of the rain fell on May 11 before an extended dry period towards the end of the month. The majority of central Iowa reporting stations’ precipitation trend graphs were similar to this one.

Table 1: Total Monthly (May 2014) Precipitation for all the ASOS stations within the Des Moines CWA.

Table 1: Total Monthly (May 2014) Precipitation for all the ASOS stations within the Des Moines CWA.

Blog post by Kenny Podrazik