Month: October 2014

Temperatures

September 2014 was slightly below normal as the statewide average temperature was 62.0°F resulting in 1.2°F below normal. For the state, it becomes the 43^rd coolest Septembers since 1872 when statewide records began.  The Des Moines CWA average temperature was also 62.0°F.  The hottest temperature was 93°F that occurred at Des Moines and Newton on the 4^th.  The coldest temperature during September in the Des Moines CWA was 31°F in Webster City, Mason City and Estherville on the morning of the 13^th. This was during the coldest stretch in September which was from the 11^th to the 16^th (See Figure 2) while the coldest day, with respect to average daily temperature, was on the 12^th  when much of central Iowa was 15 to 18 degrees below normal (See Figure 3).  In fact, Lamoni, Mason City and Ottumwa all set new record low temperatures on the morning of the 13^th (See Table 1). Also, a few areas of frost developed during the aforementioned cold stretch, mainly occurring across northern Iowa (See Figure 4).

Figure 1: Average temperatures during September 2014. Image Courtesy MRCC.

Figure 2: Average maximum temperature departure from mean during the stretch from September 11 to 16, 2014. Image Courtesy MRCC.

Figure 3: Average temperature departure from mean on September 12, 2014. Image Courtesy MRCC.

Figure 4: Areas across the U.S. that recorded 32°F or less as of September 18, 2014. A few spots across northern Iowa where in this category by mid-September.

Precipitation

The first couple of weeks in September were cool and wet as several days across the state recorded measurable precipitation in the first half of the month. In fact, the statewide average precipitation for Iowa was 4.37 inches or 0.99 inches above normal and the average precipitation for the Des Moines CWA was 4.07 inches during the month of September (See Figure 5). The highest monthly total, within the DMX CWA, was 7.41 inches in Indianola while the highest in the state was 8.63 inches near Norwalk. The greatest rainfall event came on the 9^th where a widespread band of 1 to 4 inches affected central to southern Iowa (See Figure 6). Des Moines, Lamoni, and Ottumwa recorded 3.00”, 3.62”, and 2.20” respectively. Both Des Moines and Ottumwa set new daily rainfall records on the 9^th.  The previous record at Des Moines was 1.92” set in 1970 and was the 7^th highest one-day rainfall total during the month of September (See Table 2). The previous record at Ottumwa was 2.00” set in 1921. Northern Iowa was closer to normal or even slightly below normal for monthly precipitation at some locations. Estherville, Mason City and Waterloo were all below normal during September.

Figure 5: Accumulated precipitation departure from mean during the month of September 2014. Image Courtesy MRCC.

Figure 6: Accumulated precipitation departure from mean during the month of September 2014. Image Courtesy MRCC.

Blog post by Kenny Podrazik – NWS Des Moines

Temperature

The statewide average temperature during the month of August was 71.5°F which was normal but still becomes the 60^th 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 13^th and the hottest temperature was 94°F at Lamoni on the 25^th. The hottest period was on the 24^th and 25^th 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 24^th, 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 5^th 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 12^th and 13^th 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.

Precipitation

The statewide average precipitation was 6.02 inches resulting in being 1.82 inches above normal. As a result, August 2014 becomes the 14^th 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 15^th to 16^th, 22^nd, 23^rd, 28^th, and on the 31^st over portions of western and southern Iowa (See Figures 5 & 6). The 31^st 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 28^th 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.

Reservoir Summary

Blog post by Kenny Podrazik – NWS Des Moines