The statewide average temperature for Iowa in August 2015 was 69.2°F which was 2.3°F below normal (See Figure 1). August 2015 became the 27th coolest August out of 143 years of records for the state of Iowa. This is the 4th consecutive month with the temperatures being below normal. Actually, throughout the month of August 2015, there were no long duration heat waves, just a few isolated days reaching the lower 90s early in the month. The hottest temperature in the state during the entire month was only 94°F at Sheldon on the 2nd. Des Moines recorded 93°F on the same day and that was 1 of only 2 days in which Des Moines reached 90°F or greater. The 2nd time was on the 7th when it reached 90°F on the nose. The coldest temperature throughout the month was 40°F in Spencer on the 25th. The coldest high temperature at Des Moines was 68°F on the 19th and the lowest temperature was 53°F on the 25th and 26th. Waterloo reached exactly 90°F only once and that occurred on the 2nd and its coldest temperature in August was 45°F on the 26th. On the 18th and 19th, Waterloo had back-to-back days of highs remaining in the 60s and from the 18th to the end of the month, only 2 days had a daily average temperatures that were above normal. Waterloo for the month was 2.4°F below normal for a monthly average temperature while Des Moines was 1.2°F below normal for a monthly average temperature. In Ottumwa, it was 2.7°F below its normal monthly average temperature for August.
Figure 1: Average statewide monthly temperature departure from normal for August 2015. Image is courtesy of High Plains Regional Climate Center (HPRCC).
The average statewide precipitation was 5.42 inches or 1.22 inches above normal for the month of August 2015 (See Figures 2 to 4). This is the 21st wettest August among 143 years of records and was the fourth consecutive month with above normal rainfall. The average statewide precipitation during the first half of August was 1.30 inches which was 0.92 inches below normal. A few light rain events occurred during the first couple of weeks with only one significant severe weather event on the 2nd and a heavy rain event that transpired on the evening of the 8th into the early morning on the 9th. On August 2nd, a tornado brought EF1 damage to Adair and Adams Counties as it was on the ground for 36 minutes covering 7.54 miles (See Figures 5 & 6). During the 8th and 9th, a swath of heavy rain fell from Webster County through Story, Boone, and Jasper Counties and southeast into Poweshiek County where roughly 2 to 5 inches of rain fell (See Figure 7). Heavy rain also fell over portions of far southwest Iowa on the 8th. The highest preliminary rainfall report was 7.00” in Otho, Iowa in Webster County on August 8, 2015. More widespread rain events occurred during the final two weeks of the month when the state averaged 4.12 inches or 2.14 inches above normal during that time frame. Heavy rain fell on the 17th and 18th over central to northwest Iowa (See Figure 8). Des Moines picked up 2.46 inches on the 18th, well over half of its monthly total of 4.25 inches. However, the most notable heavy rain event occurred on the 28th when a widespread 3 to 7 inches fell over portions of central Iowa with an isolated amount over 9 inches reported in Dayton, Iowa in Southeast Webster County (See Figure 9). A major flash flood on the Skillet Creek affected much of the town of Dayton as a result of the large amount of rain (See Figures 10 & 11). One other notable event that was related to weather was a lightning strike on August 23 that struck a corn stover bale storage unit near Maxwell and set it on fire (See Figure 12). The fire blazed for roughly a full day before burning out and was seen on radar for a good portion of the day on August 23 (See Figure 13).
Figure 2: Total precipitation for the state of Iowa during August 2015.
Figure 3: Total precipitation departure from normal for the state of Iowa during August 2015.
Figure 4: Total precipitation percent of mean for the state of Iowa during August 2015.
Figure 5: August 2, 2015 EF1 tornado track in Adair and Adams County.
Figure 6: August 2, 2015 EF1 tornado track in Adair and Adams County. Photo is courtesy of Adam Amdor via Twitter (@Amdor_7).
Figure 7: August 8-9, 2015 observed precipitation.
Figure 10: Major Flash Flooding on the Skillet Creek affected the Golf course in Dayton, Iowa. Photo is courtesy of James Hobbs and Jennifer Eckert.
Figure 11: Major Flash Flooding on the Skillet Creek affected the Campground in Dayton, Iowa. Photo is courtesy of James Hobbs and Jennifer Eckert.
Figure 8: Q3 radar estimated precipitation from August 18, 2015.
Figure 9: The observed significant amount of rain on August 28, 2015.
Figure 12: Lightning started a fire of a corn stover storage unit near Maxwell, Iowa on August 28, 2015. Photo is courtesy of Melissa Spencer, Story County EMA.
Blog Post by Kenny Podrazik – NWS Des Moines