The quality controlled Iowa COOP data for September 2013 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 66.9° or 3.7° above normal while precipitation totaled 2.05 inches or 1.33 inches less than normal. This ranks as the 19th warmest and 29th driest September among 141 years of records. A warmer September was last recorded in 2005 while this month's low precipitation total still exceeds the September totals of three of the past four years.

Temperatures. Higher than normal temperatures were the rule for most of September. Temperatures reached or exceeded 100° on the 7th, 9th and 10th. The highest readings were 102° temperatures recorded at Donnellson and Keokuk on the 9th. Not since September 9, 1955 (104° at Missouri Valley) had a higher reading been recorded in Iowa for so late in the year. This was also the first time that three September dates reached triple digits in Iowa since 1955, but was far from the record of ten such days recorded in September 1897. Daily temperatures averaged ten or more degrees above normal on the 7th-11th, 18th-19th and 26th-27th. Donnellson and Keosauqua each recorded 11 days with temperatures at or above 90° compared to a September normal of three such days. On the other extreme, Spencer, Battle Creek and Sheldon recorded morning lows of 32° on the 21st. This freeze occurred about one week earlier than usual for northwest Iowa but no crop damage was reported.

Cooling Degree Day Totals. Home air conditioning requirements, as estimated by cooling degree day totals, averaged 96% greater than last September and 83% greater than normal. Cooling degree day totals for the year-to-date are running 22% less than last year at this time, but 9% more than normal.

Precipitation. The very dry weather pattern that began in late June over much of Iowa continued through September in most areas. A very welcome period of frequent rainfall occurred between the 14th and the 19th with locally heavy rain falling in a band from southwest into east central Iowa. However, despite this period of precipitation, monthly totals were below normal except for a few southwestern Iowa locations. September totals varied from only 0.32 inches at Sioux Center to 7.14 inches near Hastings in Mills County. Sioux Center's total is the second lowest among 111 years of September data at that location (0.15" in 1899). Thanks to a record wet spring, year-to-date precipitation totals remain above normal over about the northeast one-half of Iowa with the state as a whole averaging nearly ten inches more precipitation this year than at the same point in 2012. Nevertheless, the July 1 to September 30 statewide average precipitation total of 5.38 inches is second only to 1947's total of 5.26 inches (normal for the period is 12.08 inches).

Severe Weather. The relatively quiet Iowa severe weather season continued through September. However, high winds, along with some large hail, were reported from 19 counties on the afternoon and evening of the 19th.

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

                 _______________2013_________________________2012
                 SEP  AUG  JUL  JUN  MAY  APR  MAR  FEB  JAN  DEC
Maximum High:    364  160   13   43  169   28    0    0  157   87
Minimum High:      9  102  204   97  311  358    9   10   20    2
Maximum Low:     213  183   58   50   61   28    0    1   79   33
Minimum Low:      32   96  217   53  116  319   35    0    0    0
Maximum Precip:   82   44   51  103  302  226   74   82   93   91

The following is some bulk statistics on how well IEM's daily COOP data estimator is performing on a monthly basis versus this QC'd dataset.

                 ______2013____________________________________
                 SEP   AUG   JUL   JUN   MAY   APR   MAR   FEB
High Temp Bias   0.2   0.2   0.4   0.4   0.1   1.3   0.8   1.0
High Temp RMSE   0.9   0.8   0.9   0.8   0.8   1.6   1.1   1.3 
Low  Temp Bias   1.3   1.2   0.8   1.2   1.2   2.5   2.2   2.5
Low  Temp RMSE   1.8   1.6   1.3   1.4   1.5   2.6   2.3   2.6
Precip    Bias  -0.08  0.00 -0.08 -0.39 -0.87 -0.56 -0.14  0.01
Precip    RMSE   0.46  0.50  0.53  0.94  1.28  0.91  0.42  0.35