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