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1108 Views September COOP Data Uploaded


The quality controlled Iowa COOP data for September 2016 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 67.3° or 4.1° above normal while precipitation totaled 6.19 inches or 2.81 inches above normal.   This ranks as the 15th warmest and 13th wettest September among 144 years of state records.   A wetter September last occurred in 1986 while a warmer one came just last year.

Temperatures. Above normal temperatures were the rule for most of the month with below normal readings confined to the 1st-3rd, 10th-11th, 13th and 28th.   There were six days averaging more than ten degrees above normal (6th and 20th through 24th) while the 2nd was the most unusually cool at just 3.7 degrees below normal.   Temperatures extremes varied from highs of 94° at Burlington on the 6th and at Algona, Atlantic, Clarion, Indianola and Sigourney on the 21st.   The lowest temperatures occurred at Spencer Airport on the mornings of the 29th and 30th with 38° readings, which was also matched at Sheldon on the 29th.   This was the highest statewide September minimum temperature on record (old record of 36° in 1905 and 1987).

Cooling Degree Days. Home air conditioning requirements, as estimated by cooling degree day totals, averaged 62% greater than normal but 24% less than last September.   Cooling degree day totals for the year-to-date are running 21% greater than last year and 17% greater than normal.

Precipitation. The big weather news for the month was the excessive rains over central and northern Iowa on the 9th-10th, 15th-16th and 21st-23rd.    The first of these three events brought rain statewide with Clarksville reporting the most rain with 4.35 inches.   The second event brought the most widespread heavy rains of the month with a maximum of 5.35 inches near Blencoe in Monona County.   However, the most destructive event was the final one.   This last event largely left the southern one-third of Iowa dry but dumped 10.56 inches of rain near Nora Springs and 9.44 inches near Nashua.   Major flooding occurred across much of north central and northeast Iowa and locations downstream of the heaviest rains.   The Shell Rock River at Shell Rock set a record flood crest 1.15 feet higher than the old record of June 2008.   Flooding along the Cedar River at Cedar Falls, Waterloo and Cedar Rapids was the second highest of record behind the disastrous floods of 2008.   Monthly rain totals of ten inches or more were fairly common across the north one-third of the state while parts of southeast Iowa were unusually dry.   Monthly rain totals varied from only 0.90 inches at Fairfield (less than one-third of normal) to 17.25 near Nora Springs.   A higher September rain total than that at Nora Springs has been recorded in only two other years in Iowa (1926 and 1970).   Record high September rain totals were set at the following locations:
StationSep 2016 TotalPrevious Sep RecordPeriod of Record
Charles City15.83 inches12.51 in 1965 134 years
Decorah11.6611.21 in 1972 134 years
Tripoli11.498.02 in 1965 69 years
New Hampton11.179.82 in 1965 115 years
Postville10.78 8.82 in 1931 75 years
Emmetsburg10.039.82 in 1964 75 years
Sheldon9.699.52 in 1926 106 years

September was the fourth consecutive very wet month across parts of northeastern Iowa.   As a result, with three months remaining in the year, record annual precipitation totals have already been established at the following locations:
Station2016 TotalPrevious Annual RecordPeriod of Record
Charles City51.93 inches51.35 in 1999 133 years
Decorah51.71 inches48.74 in 2007 128 years
Cresco50.90 inches47.87 in 1951 110 years
Osage45.98 inches45.72 in 1999 112 years

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:    225   32   17  238   65   84  135  213   29  244
Minimum High:     15   53  224   17   81   72    5   59   98   13
Maximum Low:     338   83  131  196   21   63  268  159   89  467
Minimum Low:       4   14   82   42   72   53   10   19   63    5
Maximum Precip:  295  196  151   84   92   72  124  141  156  439

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   0.1   0.1   0.1   0.2  -0.1   0.2   0.4   0.6   0.3
High Temp STD    2.0   1.8   1.9   2.1   2.0   2.5   2.6   2.4   2.1
Low  Temp Bias   0.1   0.1   0.2   0.2   0.2   0.2   0.3   0.2   0.2
Low  Temp STD    2.3   2.0   2.0   2.3   2.5   2.4   2.7   2.4   2.5
Precip    Bias  -0.01 -0.01 -0.02 -0.02  0.00  0.00  0.00  0.01 -0.01
Precip    STD    0.27  0.30  0.29  0.25  0.17  0.11  0.09  0.07  0.27