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1022 Views August COOP Data Uploaded


The quality controlled Iowa COOP data for August 2017 has been uploaded to the IEM. These observations are kindly provided by Harry Hillaker, our state climatologist, who passes along these notes on the month:

General Summary. Iowa temperatures averaged 68.0° or 3.5° below normal while precipitation totaled 3.99 inches or 0.21 inches less than normal.   This ranks as the 15th coolest and 58th wettest August among 145 years of records.   A cooler August was last recorded in 2004 and a drier one in 2013.

Temperatures. Mild weather was the rule throughout the month with only five days (1st, 16th-17th, 20th-21st) averaging just slightly warmer than normal.   The highest temperatures for the month were 93° readings at Donnellson on the 2nd and at Keosauqua on the 10th.   There were no ninety degree readings anywhere in the state after the 19th and most of central and northern Iowa never reached 90 during the month.   At Northwood the highest temperature recorded during August was only 81°.   Daytime high temperatures reached only 64° at Sheldon on the 3rd and 66° at Sioux City on the 5th.   The lowest minimum temperatures were 44° readings at Chariton on the 12th and also at Stanley on the 23rd.

Cooling Degree Day Totals. Home air conditioning requirements, as estimated by cooling degree day totals, averaged 52% less than normal and 48% less than last August.   Thus far this air conditioning season cooling degree day totals are running 16% less than last season at this time and 5% less than normal.

Precipitation. As has been the case all summer rainfall totals varied widely across the state.   However, the June and July pattern of wet weather over northeast and east central Iowa and dry elsewhere reversed in August.   A wet period from the 14th through the 21st brought the bulk of the month’s rain (2.75 inches statewide average).   Locally heavy rains fell twice in west central Iowa.   The first event was centered across northern Harrison County with 5.16 inches of rain north of Woodbine on the 15th-16th.   The second event was more widespread on the morning of the 21st with a maximum reported rain total of 6.47 inches at Denison.   The 21st brought the most widespread rain of the summer and frustrated many Iowan’s plans for viewing the solar eclipse that early afternoon.  This period of rain greatly reduced or eliminated drought conditions over most of the western one-third of Iowa.   However, severe to extreme drought conditions persisted over south central Iowa where August rainfall was still much less than normal, despite being much greater than seen in June or July.    Monthly rain totals varied from only 0.50 inches near Muscatine to 10.94 inches near Milford.   At Milford this was their highest August total among 81 years of record (old record 8.93 in 1979).   Mapleton also set an August record with 10.40 inches among 80 years of record (old record 9.86 in 1962).

Summer Summary. Precipitation averaged below normal for all three summer months with a statewide average of 10.65 inches or 3.06 inches less than normal.   The unseasonably cool August cancelled out the relatively hot June and July with a statewide average temperature of 71.3°or 0.3° below normal.   This ranks as the 72nd warmest and 38th driest summer among 145 years of records.   A lower summer rainfall total has been recorded only twice (2012 and 2013) in the past 14 years.   At Fairfield only 3.51 inches of rain fell this summer, breaking the previous summer-time low of 3.77 inches set in 1911 among 137 years of records.   Meanwhile Fayette recorded 22.67 inches of rain, their sixth highest summer total among 126 years of record.

The following is the number of new daily records set at COOP sites based on data back to 1951.

                 AUG  JUL  JUN  MAY  APR  MAR  FEB  JAN  DEC  NOV 
Maximum High:      0    1   28   36    5   92  546   43   40  226
Minimum High:     41    0    8  189  122   22    0   36   44   21
Maximum Low:       0   12   95   13   43   43  154  367   70  125
Minimum Low:      23    1   59    5   12   42    0   23   99   15
Maximum Precip:   47   38   35   39   97   40   55  219  167   85

The following is a table summarizing how well the IEM daily data estimator is working in comparison to the quality controlled data.

                      2017                                   2016 
                 AUG   JUL   JUN   MAY   APR   MAR   FEB   JAN   DEC
High Temp Bias  -0.4  -0.2   0.1  -0.2  -0.3  -1.0  -0.9   0.2   0.3
High Temp STD    M     M     M     M     M     M     M     2.0   2.0
Low  Temp Bias  -0.3  -0.3   0.1  -0.2  -0.3  -0.4  -0.2   0.0   0.1 
Low  Temp STD    M     M     M     M     M     M     M     2.3   2.3
Precip    Bias  -0.05  0.14  0.08  0.07  0.02  0.05  0.05  0.01 -0.02
Precip    STD    0.70  0.75  0.66  0.42  0.49  0.39  0.33  0.07  0.07

The standard deviations are missing this month due to some new code that is not behaving as I expected. Just haven't allocated time to figure out why yet, sorry.