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1857 Views September COOP Data Uploaded


The quality controlled Iowa COOP data for September 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 66.7° or 3.5° above normal while precipitation totaled 2.34 inches or 1.04 inches below normal.   This ranks as the 15th warmest and 45th driest September among 145 years of records.   Last September was slightly warmer while a drier September was last recorded in 2013.

Temperatures. The unseasonably cool weather pattern that began on July 28 continued through the first eight days of September.   Only six days in this 43 day period averaged warmer than normal.   However, the opposite weather pattern began on September 9 with all but two days of the remainder of the month averaging warmer than normal.   The temperature reached 90° at Osceola on the 13th, the first time ninety had been reached anywhere in the state since August 19.   Temperatures climbed into the nineties on ten days between the 13th and the 25th.   Iowa City Airport reported the highest temperature of the month with a 95° reading on the 23rd.   On the other extreme morning lows dipped to 35° at Stanley on the 7th and at Cresco on the 30th.   September as a whole averaged just 1.3° cooler than August (1897 was the only year to have a September average warmer than August).

Cooling Degree Day Totals. Home air conditioning requirements, as estimated by cooling degree day totals, averaged 1% less than last September but 63% more than normal.   Thus far this air conditioning season cooling degree day totals are running 14% less than last year at this time and 2% more than normal.

Precipitation. Exceptionally dry weather prevailed over the first one-half of the month with a statewide average rainfall of only 0.07 inches during the period compared to a normal of 1.77 inches.   The second one-half of the month brought an average of 2.27 inches of rain compared to a normal of 1.61 inches.   Greatest rains during the month were concentrated over west central Iowa, however, torrential rains fell across small portions of southeastern Iowa on the 20th-21st with a location just south of Ottumwa picking up 7.75 inches of rain overnight.   Monthly rain totals varied from only 0.05 inches just south of Burlington to 9.08 inches just south of Ottumwa.   Two locations recorded their driest Septembers on record.   Anamosa saw 0.36 inches in the month, slightly less than their previous record of 0.38 inches set in 1976 among 88 years of records at that location.   The Dubuque Lock & Dam also set a record low with 0.23 inches with their previous record of 0.51 inches set in 1990 among 81 years of records.   Burlington’s low total failed to set a record with 1979 having brought only a trace of rain during September.   Year-to-date precipitation totals vary from only 18.37 inches at Sigourney (nearly 12 inches below normal) to 41.38 inches at Little Sioux (about 13 inches above normal).   Above normal annual totals are mostly confined to the western and northern one-thirds of the state.   Extreme drought persists over parts of eight south central Iowa counties.

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

                 SEP  AUG  JUL  JUN  MAY  APR  MAR  FEB  JAN  DEC
Maximum High:    360    0    1   28   36    5   92  546   43   40
Minimum High:     15   41    0    8  189  122   22    0   36   44
Maximum Low:     129    0   12   95   13   43   43  154  367   70
Minimum Low:       3   23    1   59    5   12   42    0   23   99
Maximum Precip:   27   47   38   35   39   97   40   55  219  167

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

                 SEP   AUG   JUL   JUN   MAY   APR   MAR   FEB   JAN
High Temp Bias  -0.2  -0.4  -0.2   0.1  -0.2  -0.3  -1.0  -0.9   0.2
High Temp STD    M     M     M     M     M     M     M     M     2.0
Low  Temp Bias   0.2  -0.3  -0.3   0.1  -0.2  -0.3  -0.4  -0.2   0.0 
Low  Temp STD    M     M     M     M     M     M     M     M     2.3
Precip    Bias  -0.05 -0.05  0.14  0.08  0.07  0.02  0.05  0.05  0.01
Precip    STD    0.64  0.70  0.75  0.66  0.42  0.49  0.39  0.33  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.