News and Notes

The quality controlled Iowa COOP data for April 2016 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 49.9° or 1.0° above normal while precipitation totaled 3.25 inches or 0.26 inches less than normal.   This ranks as the 57th warmest and 56th wettest April among 144 years of records.

Temperatures. April opened and closed with mostly cooler than normal weather.   However, above normal temperatures prevailed every day from the 13th through the 26th.    The most noteworthy temperature events of the month were a pair of hard freezes on the 9th and 12th.   The 9th was the coldest day over most of the state with temperatures falling into the teens over much of the northwest two-thirds of Iowa.   The lowest temperature recorded on the 9th was 13° at Audubon while readings on the 12th fell to 16° at Sheldon, Spencer and Webster City.   There was some freeze injury to fruit trees, however, damage was not as great as feared given the advanced stage of development of vegetation which resulted from an extended period of very mild weather in March.   The month’s highest temperatures were 85° readings at Little Sioux on the 3rd and Donnellson on the 25th.   April came to an end with cloudy, cool and wet weather holding daytime highs down in the forties in many areas from the 27th through the 30th.

Heating Degree Days. Home heating requirements, as estimated by heating degree day totals, averaged 7% greater than last April, but 8% less than normal.   Degree day totals for the heating season-to-date (from July 1, 2015) are running 15% less than last season at this time and 14% less than normal.

Precipitation. Unseasonably dry weather prevailed for the first 18 days of the month when no measurable rain fell over parts of west central and southwest Iowa.   This dry period allowed an unusually early start to the corn planting season but for a time also delayed germination of specialty crops owing to dry topsoil.   Rainfall was much more frequent and plentiful for the final dozen days of April.   Late-month rainfall was particularly heavy over western Iowa where numerous rivers and streams reached or slightly exceeded flood stage.   The state-wide average precipitation averaged only 0.57 inches for the first 18 days of April but rebounded to 2.68 inches for the final 12 days of the month.   April precipitation totals were above normal over most of the western one-third of Iowa and driest over north central and northeast Iowa where monthly totals were under one-half of normal in some areas.   April rain totals varied from only 0.75 inches at Marquette to 7.52 inches at Alta.   At Guttenberg this was the driest April since 1942 while at Sioux City this was the wettest April since 1998.   Precipitation was widespread on the last day of the month.   However, much of this precipitation fell after the final rain measurements of the month ( made at 7 a.m. or 8 a.m. daily at most locations) and will be included in the May 2016 statistics.

Severe Weather. Severe thunderstorm activity was minimal during April and was limited to only the 24th and 27th.   High winds and hail were recorded within a narrow band of northwest Iowa on the 24th, roughly between Sioux City and Estherville.   There were also five short-lived tornadoes confirmed in southwest Iowa on the 27th, along with a few scattered hail reports.   However, April began with frequent non-thunderstorm high wind events with wind gusts of 40 mph or higher recorded on 8 of the first 9 days of the month (early April on average is the windiest time of the year in Iowa).

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

                 2016______________________2015__________________
                 APR  MAR  FEB  JAN  DEC  NOV  OCT  SEP  AUG  JUL
Maximum High:     84  135  213   29  244   85   75  130   25   22
Minimum High:     72    5   59   98   13   56   21   13  269  261
Maximum Low:      63  268  159   89  467  171   79  336   38   54
Minimum Low:      53   10   19   63    5   58   20   25  156  139
Maximum Precip:   72  124  141  156  439  316  162  150  158  214

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

                 2016                  2015
                 APR   MAR   FEB   JAN   DEC   NOV   OCT   SEP   AUG
High Temp Bias   0.2   0.4   0.6   0.3   0.2   0.3   0.2   0.0   0.1
High Temp STD    2.5   2.6   2.4   2.1   2.0   2.2   1.8   1.7   1.8
Low  Temp Bias   0.2   0.3   0.2   0.2   0.1   0.2   0.1   0.0   0.2
Low  Temp STD    2.4   2.7   2.4   2.5   2.2   2.7   2.6   2.1   2.1
Precip    Bias   0.00  0.00  0.01 -0.01 -0.01 -0.00 -0.01  0.01 -0.01
Precip    STD    0.11  0.09  0.07  0.27  0.14  0.14  0.08  0.26  0.27