July 2015 Iowa Monthly Review

Temperatures

The statewide average temperature for July 2015 was 72.2°F or 1.4°F resulting in the 27th coolest July out of 143 years of statewide climate records (See Figure 1). Unseasonably cool temperatures resulted in below normal values during the first week and a half of July (See Figure 2), which was the primary culprit for the entire month being below normal. Des Moines saw 3 days when the average daily temperature was 10-11°F below normal and Waterloo had 4 days in which the daily average temperature was 11-12°F below normal. Low temperatures dipped into the lower 50s over much of central Iowa through the 10th. 44°F was the coldest temperature during the month and occurred in Cresco and Elkader on the 2nd and then again on the 3rd at Spencer. Lamoni and Ottumwa set new record low temperatures on the 8th with minimums of 57°F and 55°F respectively. Both records were previously set back in 2006 and Lamoni’s previous record was 61°F and Ottumwa’s was 56°F. Summer-like temperatures returned during the middle of the month (13th to 20th). The overnight lows were well above normal and was the main reason this period resulted in being above normal for average temperatures (See Figures 3 & 4). One of the hottest days of the month occurred on the 13th when temperatures rose well into the 90s. Des Moines had the warmest temperature during the month when it topped 97°F on the 13th, but just a few days later on the 17th, Bellevue, Lamoni, and Osceola rose 97°F on the 17th. Hot and humid conditions affected the state during the middle of the month when heat index readings of 105°F to 111°F were reported from the 11th to 13th (See Figure 5). Temperatures through the last 10 days were relatively normal with a couple of hot days occurring on the 24th and 28th when heat index readings jumped back to 100°F to 110°F.

Figure 1: Average Maximum Temperatures Departure from Mean during July 2015 shows maximum temperatures were below normal.

Figure 1: Average Maximum Temperatures Departure from Mean during July 2015 shows maximum temperatures were below normal.

Figure 2: Average Temperature Departure from Mean from July 1 to July 10, 2015.

Figure 2: Average Temperature Departure from Mean from July 1 to July 10, 2015.

Figure 3: Average Maximum Temperature Departure from Mean from July 13 to July 20, 2015.

Figure 3: Average Maximum Temperature Departure from Mean from July 13 to July 20, 2015.

Figure 4: Average Maximum Temperature Departure from Mean from July 13 to July 20, 2015.

Figure 4: Average Maximum Temperature Departure from Mean from July 13 to July 20, 2015.

Figure 5: Maximum Heat Index Forecast for July 13, 2015.

Figure 5: Maximum Heat Index Forecast for July 13, 2015.

Precipitation

The statewide average precipitation was 5.71 inches or 1.21 inches above normal which made July 2015 the 19th wettest July out of 143 years of statewide precipitation records (See Figures 6 & 7). However, dry conditions affected the state during the first couple of weeks as the statewide average precipitation was 1.64 inches (See Figure 8). Normal value is 2.28 inches during this time frame. In fact, the first half was so dry that ‘abnormally dry’ conditions crept into northwest Iowa by July 14 according to the Drought Monitor (See Figure 9). The last half of the month however was much more active and the statewide average precipitation was 4.07 inches (See Figure 10). Normal during that period is 2.22 inches. There were a few days during the first half the month where with locally heavy rain occurred. The 6th and the 15th all had locally heavy rain over portions of southern to southeast Iowa, while on the 11th more widespread rain cause some flash flooding over southern Iowa (See Figure 11). The most active week for rainfall was from July 24th to the 28th, with southern Iowa receiving the majority of the rain (See Figure 12). However, northern Iowa had its share of heavy rain on the 24th when Mason City picked up 4.13 inches. Spring Hill, in Warren County, received the month’s heaviest rain on the night of the 28th with 6.32 inches. The monthly rainfall totals ranged from a low of 1.20 inches in Dubuque to a whopping 13.33 inches in Knoxville. Des Moines totaled 7.17 inches which was 2.70 inches above normal and Waterloo totaled 5.56 inches or 1.29 inches above normal. In fact, Des Moines had 7 days with measurable precipitation from July 15-28 and had 3 consecutive days with 1 inch or more from 26-28.

Severe weather was limited during the month of July with just a handful of localized areas that were impacted over central Iowa. In fact, the NWS Des Moines office did not issue a Severe Thunderstorm Warning until July 13! One notable event occurred on July 16 when several reports of funnel clouds were received late in the afternoon in Story County (See Figures 13 & 14).

Figure 6: Accumulated Precipitation during the month of July 2015.

Figure 6: Accumulated Precipitation during the month of July 2015.

Figure 7: Accumulated Precipitation Percent of Mean during the month of July 2015. Southern received the bulk of the rainfall.

Figure 7: Accumulated Precipitation Percent of Mean during the month of July 2015. Southern received the bulk of the rainfall.

Figure 8: Accumulated Precipitation Department from Mean from July 1 to July 14, 2015.

Figure 8: Accumulated Precipitation Department from Mean from July 1 to July 14, 2015.

Figure 10: Accumulated Precipitation Department from Mean from July 15 to July 31, 2015.

Figure 10: Accumulated Precipitation Department from Mean from July 15 to July 31, 2015.

Figure 9: U.S. Drought Monitor showed drought conditions creeping into northwest Iowa.

Figure 9: U.S. Drought Monitor showed drought conditions creeping into northwest Iowa.

Figure 11: Radar estimated precipitation on July 11, 2015 over southern Iowa. A widespread swath of 3-5 inches accumulated with a few locally higher amounts.

Figure 11: Radar estimated precipitation on July 11, 2015 over southern Iowa. A widespread swath of 3-5 inches accumulated with a few locally higher amounts.

Figure 12: 5-Day radar estimated precipitation ending 10:41 p.m. on July 29, 2015 where the most of the heavy rain fell over southern Iowa.

Figure 12: 5-Day radar estimated precipitation ending 10:41 p.m. on July 29, 2015 where the most of the heavy rain fell over southern Iowa.

Figures 13 & 14: Reports of funnel clouds on July 13 near Ames, Iowa were shown on Twitter.

Figures 13: Reports of funnel clouds on July 13 near Ames, Iowa were shown on Twitter.

Figures 13 & 14: Reports of funnel clouds on July 13 near Ames, Iowa were shown on Twitter.

Figures 14: Reports of funnel clouds on July 13 near Ames, Iowa were shown on Twitter.

A few statewide climate statistics were courtesy of State Climatologist Harry Hillaker: http://www.iowaagriculture.gov/climatology/weatherSummaries/2015/pms201507.pdf
Blog Post by Kenny Podrazik – NWS Des Moines