The statewide average temperature during the month of August was 71.5°F which was normal but still becomes the 60th coolest August among 142 years of records. It was an interesting temperature trend in August as the first half of the month was well below normal, while the last half was above normal (See Figures 1 and 2). Hence, both halves balanced each other out resulting in near normal temperatures for August across central Iowa. In the DMX CWA, the coldest temperature was 47°F at Chariton on the 13th and the hottest temperature was 94°F at Lamoni on the 25th. The hottest period was on the 24th and 25th when much of central Iowa reached the lower 90s for high temperatures (See Figure 3). In fact, Mason City finally reached a maximum temperature of 91°F on the 24th, breaking the consecutive streak of days without reaching 90°F. The number of days was 348 which began on September 10, 2013 and was the 5th longest stretch of its kind at Mason City. Des Moines only reached 90°F 3 times in August but normally has about 7 days that reach 90°F. Typically Waterloo reaches 90°F or greater 6 days during August, but only 3 days topped that mark. One of the colder stretches during the month was on the 12th and 13th when several low temperatures dipped into the 40s and 50s resulting in several degrees below normal (See Figure 4).
Figure 1: Average Temperature Departure from Mean from August 1 to August 16, 2014. Temperatures were roughly 2 to 4 degrees below normal for central Iowa. The DMX CWA is outlined in white.
Figure 2: Average Temperature Departure from Mean from August 17to August 31, 2014. Temperatures were roughly 2 to 4 degrees above normal for central Iowa. The DMX CWA is outlined in white.
Figure 3: Maximum temperatures on August 24-25, 2014 were well into the 80s and into the lower 90s across central Iowa.
Figure 4: Minimum temperatures on August 12-13, 2014 were 6-9 degrees below normal across central Iowa. The DMX CWA is outlined in white.
The statewide average precipitation was 6.02 inches resulting in being 1.82 inches above normal. As a result, August 2014 becomes the 14th wettest (out of 142) August on record. Several heavy rain events and a couple severe weather events affected central Iowa in August. The most significant heavy rain fell on August the 15th to 16th, 22nd, 23rd, 28th, and on the 31st over portions of western and southern Iowa (See Figures 5 & 6). The 31st was the most widespread severe weather event when a line of thunderstorms produced severe wind damage and a pair of tornadoes. The latter half of the month became the most active with thunderstorms occurring (somewhere over central Iowa) each evening or overnight hours. In fact, the last 12 days of the month, Des Moines recorded measurable precipitation on 10 days and 11 days with at least a trace. The highest amount occurred on the 28th with a whopping total of 3.38 inches at the Des Moines International Airport. This set a new daily precipitation record as it shattered the 1.74 inches previously set on August 28, 1960. Des Moines came in third all-time highest August precipitation at that location (See Figure 7). Denison (Crawford County) and Greenfield (Adair County) both set new August monthly records (See Table 1). In fact, much of central Iowa was well above normal for the month of August (See Figures 8 and 9).
Figure 5: Q3 precipitation estimated for August 22, 2014.
Figure 6: Q3 precipitation estimated for August 23, 2014 shows much of south central Iowa received another round of significant heavy rain.
Figure 8: Observed precipitation for the month of August 2014 across central IA.
Figure 9: August 2014 monthly departure from mean precipitation.
Figure 7: The Des Moines, Iowa accumulated precipitation for the month of August 2014. August came in 3rd highest August since 1878. Only 1993 and 1977 had higher precipitation totals in August at Des Moines.
August reservoir summary for Lake Red Rock and Saylorville Lake.
August summary of outflow from Lake Red Rock and Saylorville Lake
Blog post by Kenny Podrazik – NWS Des Moines