The quality controlled Iowa COOP data for April 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. Iowa temperatures averaged 50.7° or 1.8° above normal while precipitation totaled 3.37 inches of 0.14 inches below normal.   This ranks as the 40th warmest and 49th wettest April among 143 years of records.   This was the driest April since 2004.

Temperatures. The warmest day of the month was the first day when temperatures climbed into the eighties over most of Iowa and reached a maximum of 88° at Little Sioux.   Only a few locations in extreme western Iowa and far southeast Iowa reached the 80 degree mark during the remainder of the month.   The month’s lowest temperatures were 19° readings at Elkader and Belle Plaine on the morning of the 4th.   Also noteworthy was a late month cold snap that brought a hard freeze to many areas on the 22nd and 23rd with lowest readings of 22° at Cresco, Decorah, Elkader and Mason City on the 23rd.

Heating Degree Day Totals. Home heating requirements, as estimated by heating degree day totals, averaged 21% less than last April and 14% less than normal.   Thus far this heating season (since July 1, 2014) degree day totals have averaged 11% less than the harsh winter of one year ago, but 2% greater than normal.

Precipitation. Rainfall amounts varied greatly during the month with relatively wet conditions prevailing from west central to north central Iowa.   Driest conditions, with some areas seeing less than one-third of normal April amounts, were across the southeast and extreme northwest corners of the state.   Totals varied from 1.18 inches at Rock Valley to 6.88 inches at Lake Mills where localized heavy thunderstorms dumped 4.44 inches of rain between the 7th and 9th.   Moderate drought conditions have edged into far northwest Iowa in response to a dry weather pattern prevailing in that area of the state (and extending over much of Minnesota and the Dakotas) since last summer.   Snow occurred only twice during the month.   Rain turned to snow from west central to north central Iowa on the afternoon and evening of the 9th with a maximum of four inches reported at Schleswig in Crawford County.   Some snow was also reported across parts of northeast Iowa on the 21st but with no accumulation.   The statewide average snowfall was just 0.2 inches for the month while normal is 1.6 inches.   This brings the seasonal snow total to 26.8 inches or 5.4 inches below normal.   This has been only the second season in the past nine to bring a below normal total in Iowa.   This ranks as the 47th lowest seasonal total among 128 years of records.

Severe Weather. The year’s first two tornadoes were reported over east central Iowa on the evening of April 9.   Overall severe storms were infrequent during the month with a few large hail reports on the 7th, 8th, 9th, 18th and 19th with all of the reports coming from southern and eastern Iowa.

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

                 2015_____________________2014___________________
                 APR  MAR  FEB  JAN  DEC  NOV  OCT  SEP  AUG  JUL
Maximum High:     34  182   13  113   84   24   97   25   25    4
Minimum High:     28  102  364   65   60  634   89  267  161  399
Maximum Low:      34   29   25  135  451    5   56   86  113    8
Minimum Low:      76   98  345  111   28  550   22  180   33  330
Maximum Precip:  122   17  113   67  121   67  149  176  182  134

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

                 2015
                 APR   MAR   FEB   JAN
High Temp Bias   0.0   0.3   0.3   0.2
High Temp STD    2.2   2.6   2.8   2.5
Low  Temp Bias   0.3   0.4   0.3   0.1
Low  Temp STD    2.7   2.9   2.9   2.6
Precip    Bias   0.00  0.01 -0.16  0.01
Precip    STD    0.13  0.13  0.05  0.04