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2038 Views December COOP Data Uploaded


The quality controlled Iowa COOP data for December 2015 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. Temperatures averaged 32.9° or 10.0° above normal while precipitation totaled 4.90 inches or 3.56 inches above normal. This ranks as the wettest and 7th warmest December among 143 years of records. The previous wettest December was recorded in 1982 with 3.43 inches. The last warmer December was recorded in 1965.

Temperatures. Unseasonably warm weather was the rule through nearly all of December. Only one day (the 31st) brought a statewide average temperature that was below normal. This warm pattern began on August 31 with only 25 of the last 123 days of 2015 averaging below normal. The final one-third of the year averaged 5.6° above normal. Only 1931 was warmer for this late year period (when September, November and December all ranked in the top 5 warmest for their respective months). Temperature extremes for the month ranged from highs of 64° at Donnellson and Keokuk on the 12th, Bloomfield and Keosauqua on the 13th and Keosauqua again on the 23rd while Sheldon, Sioux Center and Spencer recorded the lowest temperatures with -6° readings on the morning of the 31st. There were five days (10th, 12th, 13th, 14th and 23rd) during the month when temperatures exceeded 60° somewhere in the state while only two days (3rd and 31st) brought sub-zero readings.

Heating Degree Days. Home heating requirements, as estimated by heating degree day totals, averaged 24% less than normal and 13% less than last December. Heating degree day totals so far this season (since July 1) are running 23% less than last year and 22% below normal.

Precipitation. A storm system brought heavy snow to far northwest Iowa on the last day of November with light rain and snow persisting over much of Iowa into the first two days of December. There was a welcome mostly dry period from the 3rd through the 11th. However, an unseasonably warm and humid air mass brought widespread heavy rainfall from the evening of the 12th through the morning of the 14th. An amazing statewide average of 2.82 inches of rain fell during this event. Only three winter months (December 1982, February 1881 and February 1915) have brought more precipitation to Iowa than this one storm system. Grundy Center recorded 5.98 inches of rain during this storm which easily exceeded their December monthly record precipitation total of 3.74 inches. Another storm system brought widespread rain on the 23rd with some central and northeast Iowa locations receiving over an inch of rain. The extended period of unseasonably warm and wet weather appeared to make a White Christmas impossible. However, a compact Christmas Eve storm system brought snow from southwest, through central and into northeast Iowa. Heavy snow fell from Council Bluffs to Ames with 14 inches reported at Persia is Harrison County. Finally, another large storm system brought heavy winter precipitation to much of Iowa on the 28th into the morning of the 29th. Heavy snow fell across the northern one-third of Iowa where 6 to 10 inch amounts were common. Meanwhile copious amounts of sleet and freezing rain fell over much of east central and southeast Iowa. Monthly precipitation totals (rain plus the liquid equivalent of snow and sleet) varied from 1.72 inches at Rock Rapids to 8.20 inches at Grundy Center. Grundy Center's total has been exceeded only once in Iowa during December when Keokuk recorded 8.56 inches in 1873. Dozens of cities set records for greatest December precipitation totals with a partial list below. Cherokee, Shenandoah and Storm Lake set record maximum totals for both November and December. Only two locations, Rock Rapids and Fort Madison failed to record at least double their normal December precipitation total.

CityDec. 2015 (inches)Previous Dec. Record Period of Record
Grundy Center8.203.74 in 1982123 years
Denison7.153.43 in 1984120 years
Glenwood6.744.19 in 1984127 years
Atlantic6.623.54 in 1982126 years
Clarinda6.164.73 in 1913132 years
Carroll6.093.88 in 1931128 years
Waterloo5.923.77 in 1982132 years
Logan5.804.76 in 1984146 years
Marshalltown5.603.41 in 1982134 years
Iowa Falls5.604.47 in 1982131 years
Oskaloosa5.524.16 in 2007137 years
Belle Plaine5.493.31 in 2007126 years
Dakota City5.463.72 in 2009129 years
Des Moines5.443.72 in 1931140 years
Sac City5.424.40 in 1871140 years
Indianola5.193.90 in 2009129 years
Decorah4.793.29 in 2010129 years
Storm Lake4.712.46 in 1931126 years
Cedar Rapids4.493.84 in 1982133 years
Charles City4.423.59 in 1891134 years
Mason City4.223.26 in 1982117 years
Ottumwa4.033.95 in 1895125 years

December snow totals varied from only 0.4 inches at Fort Madison to 24.9 inches at Rock Rapids. The statewide average snowfall was 9.8 inches or 1.5 inches above normal and ranks as the 29th highest December total among 129 years of records.

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

                 DEC  NOV  OCT  SEP  AUG  JUL  JUN  MAY  APR  MAR
Maximum High:    244   85   75  130   25   22   69   28   34  182
Minimum High:     13   56   21   13  269  261   88  316   28  102
Maximum Low:     467  171   79  336   38   54   32   82   34   29
Minimum Low:       5   58   20   25  156  139   26   87   76   98
Maximum Precip:  439  316  162  150  158  214  151  155  122   17

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

                 DEC   NOV   OCT   SEP   AUG   JUL   JUN   MAY   APR
High Temp Bias   0.2   0.3   0.2   0.0   0.1   0.0   0.0  -0.1   0.0
High Temp STD    2.0   2.2   1.8   1.7   1.8   1.7   1.7   2.5   2.2
Low  Temp Bias   0.1   0.2   0.1   0.0   0.2   0.2   0.2   0.1   0.3
Low  Temp STD    2.2   2.7   2.6   2.1   2.1   2.0   2.0   2.0   2.7
Precip    Bias  -0.01 -0.00 -0.01  0.01 -0.01  0.00  0.00 -0.01  0.00
Precip    STD    0.14  0.14  0.08  0.26  0.27  0.29  0.33  0.20  0.13