The quality controlled Iowa COOP data for April 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 50.8° or 1.9° above normal while precipitation totaled 3.89 inches or 0.38 inches above normal.   This ranks as the 23rd warmest and 35th wettest April among 145 years of records.   A warmer April was last recorded in 2012 and a wetter one in 2013.   This was the 13th consecutive April with a statewide average precipitation amount in excess of the historical April average of 3.05 inches (1873-2016).

Temperatures. Warmer than usual weather prevailed for 16 of the first 20 days of the month, averaging 6.3° above normal.   However, cloudy, wet and cold weather prevailed late in the month, particularly for the final five days of April which averaged 11.6° cooler than normal.   Temperature extremes for the month varied from a high of 84° at Lamoni on the 19th to a low of 20° at Battle Creek on the morning of the 7th.   However, probably the most significant temperature event of the month was a hard freeze across most of the northern one-third of Iowa on the morning of the 28th.   Temperatures fell to 22° at Mason City and Spencer.   While freezes are not uncommon at this time of year in northern Iowa the mild weather prevailing for much of the late winter and early spring accelerated development of horticultural crops and may have left them more susceptible to freeze damage.   Meanwhile, a handful of locations in far southern and extreme eastern Iowa have not recorded a freeze since March 22.

Heating Degree Day Totals. Home heating requirements, as estimated by heating degree day totals, averaged 14% less than usual during April and 7% less than last year.   Heating requirements thus far this season (since July 1, 2016) are running 16% less than normal and 2% less than last season at this time.

Precipitation. April precipitation totals varied from 1.88 inches at Estherville to 7.85 inches at Chariton.   With a few exceptions, rain totals were below normal over most of northwest and west central Iowa, roughly north and west of a line from Council Bluffs to Ames to Forest City.   At Chariton a higher April precipitation total has been recorded only twice (1897 and 1991) among 123 years of data.

Severe Weather. There were three severe weather outbreaks during the month.   The most widespread event came on the evening of the 15th with severe weather, mostly in the form of large hail, reported from 28 counties with hail to baseball size in Black Hawk and Plymouth counties.   Another event on the night of the 9th generated severe weather reports from 15 counties, again mostly in the form of hail, with largest hail of 2.5 inches in diameter from Mitchell County.   Finally, one last event on the evening of the 19th brought severe weather reports, mostly high winds, to eight counties.

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

                 2017______________________2016__________________
                 APR  MAR  FEB  JAN  DEC  NOV  OCT  SEP  AUG  JUL
Maximum High:      5   92  546   43   40  226  242  225   32   17
Minimum High:    122   22    0   36   44   21    8   15   53  224
Maximum Low:      43   43  154  367   70  125  184  338   83  131
Minimum Low:      12   42    0   23   99   15    6    4   14   82
Maximum Precip:   97   40   55  219  167   85  118  295  196  151

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

                 2017                         2016             
                 APR   MAR   FEB   JAN   DEC   NOV   OCT   SEP   AUG
High Temp Bias  -0.3  -1.0  -0.9   0.2   0.3   0.2   0.1   0.1   0.1
High Temp STD    M     M     M     2.0   2.0   2.1   2.2   2.0   1.8
Low  Temp Bias  -0.3  -0.4  -0.2   0.0   0.1   0.0   0.2   0.1   0.1
Low  Temp STD    M     M     M     2.3   2.3   2.8   2.5   2.3   2.0
Precip    Bias   0.02  0.05  0.05  0.01 -0.02  0.00  0.00 -0.01 -0.01
Precip    STD    0.49  0.39  0.33  0.07  0.07  0.09  0.12  0.27  0.30

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.