The quality controlled Iowa COOP data for December 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 17.3° or 5.6° below normal while precipitation totaled 0.65 inches or 0.69 inches below normal. This ranks as the 17th coolest and 32nd driest December among 141 years of records. A colder December was last recorded in 2000 and a drier one in 2004. Temperatures. December began with mild weather as temperatures averaged above normal for the first four days of the month with Shenandoah reaching 62° on the 2nd. However, cold weather was the rule for most of the month with temperatures averaging more than twenty degrees below normal on the 7th, 9th, 23rd and 24th. Osceola reported the lowest official temperature in the state with a -27° reading on the morning of the 24th while Sheldon had the lowest wind chill with a -38° reading on the morning of the 11th. Daytime high temperatures remained below zero in some areas on the 6th, 23rd, 29th and 31st. Much warmer air briefly edged into far western Iowa late in the month with daily record highs set on the 27th and 28th. A strong cold front, with northwest winds gusting to 61 mph, barreled into northwest Iowa during the afternoon of the 28th with the temperature at Sioux City falling from 62° at 3:07 p.m. to -3° at 8:43 the next morning (a 65° drop in less than 18 hours). The combination of cold weather and dry ground allowed soils to freeze to a depth of from 7 to 15 inches by month's end. Snow cover at month's end varied from little, if any, in the far southwest to 8 to 10 inches across the northeast. However, the mostly dry, fluffy snow has a low water content of under an inch liquid equivalent.

Heating Degree Day Totals. Home heating requirements, as estimated by heating degree day totals, averaged 27% greater than last December and 13% greater than normal. Thus far this heating season (since July 1), heating requirements are up 14% from last season and 8% from normal. This has been the coldest start to the heating season in 13 years.

Precipitation. Precipitation was relatively frequent across the state but amounts were mostly light. Monthly totals were below normal at all reporting points varying from 0.06 inches at Logan (their third lowest December total among 145 years of record) to 1.29 inches at Clinton and Wapello. The month's largest precipitation event came on the 21st-22nd with snow falling across the southeast two-thirds of Iowa. Greatest snow totals with this storm occurred in south central Iowa with nine inch totals at Blockton and Lamoni. Other notable events came on the 8th when snow fell statewide with a maximum total of 5.3 inches at Des Moines. Finally, a large winter storm just clipped the far southeast corner of Iowa on the 13th-14th with seven inches of snow at Keokuk. Monthly snow totals varied from only 0.9 inches at Holly Springs to 18.0 inches at Belle Plaine. The statewide average snowfall was 9.3 inches or one inch above normal. This ranks as the 33rd greatest December total among 127 years of records.

Annual Summary. The statewide average temperature for 2013 was 46.5° or 1.6° below normal while precipitation totaled 35.38 inches or 0.11 inches above normal. This ranks as the 25th coolest and 37th wettest year among 141 years of records. The year was noteworthy for a record wet April and May, as well as a very dry July through September period. Precipitation totals varied from 21.12 inches at Spirit Lake to 49.58 inches at Saint Ansgar.

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

                 ____________________2013________________________
                 DEC  NOV  OCT  SEP  AUG  JUL  JUN  MAY  APR  MAR
Maximum High:     21   18   31  364  160   13   43  169   28    0
Minimum High:    141  170   60    9  102  204   97  311  358    9
Maximum Low:      14   25   46  213  183   58   50   61   28    0
Minimum Low:     177  241   70   32   96  217   53  116  319   35
Maximum Precip:   41  123  138   82   44   51  103  302  226   74

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____________________________________
                 DEC   NOV   OCT   SEP   AUG   JUL   JUN   MAY
High Temp Bias   0.7   1.1   0.2   0.2   0.2   0.4   0.4   0.1
High Temp RMSE   1.0   1.3   0.7   0.9   0.8   0.9   0.8   0.8
Low  Temp Bias   1.3   1.2   1.4   1.3   1.2   0.8   1.2   1.2
Low  Temp RMSE   1.6   1.5   1.7   1.8   1.6   1.3   1.4   1.5
Precip    Bias   0.24  0.09  0.18 -0.08  0.00 -0.08 -0.39 -0.87
Precip    RMSE   0.31  0.28  0.59  0.46  0.50  0.53  0.94  1.28