News and Notes

The quality controlled Iowa COOP data for May 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 59.5° or 0.6° below normal while precipitation averaged 4.54 inches or 0.02 inches below normal.   This ranks as the 65th coolest and 53rd wettest May among 144 years of records.

Temperatures. The first five days of May brought below normal temperatures with a few locations reporting a light frost on the mornings of the 2nd, 3rd and 5th.   Above normal temperatures prevailed from the 6th through the 11th with Iowa’s first ninety degree readings of the year recorded at Marion, Guttenberg and Hawarden on the 6th.   Unseasonably cool weather was the rule at mid-month with below normal temperatures each day from the 12th through the 21st.   Freezes were reported in some areas on the 14th, 15th and 18th with the most widespread freeze centered upon northeast Iowa on the 15th when Cresco, Decorah and Elkader recorded 27° minimums.   Finally, the month finished with a string of ten consecutive warmer than normal days with the highest temperatures reported from Little Sioux and Lamoni at 89° on the 30th.

Heating Degree Days. Home heating requirements, as estimated by heating degree day totals, averaged 15% greater than last May and 8% more than normal.   However, heating requirements for the entire 2015-2016 season are running 15% less than last season at this time and 13% less than normal.

Precipitation. As with temperatures, there were alternating periods of below and above normal precipitation.   A wet period which began in late April continued into May 1.   Mostly dry weather prevailed from the 2nd through the 8th, especially across western Iowa where the second one-half of April had been very wet.   Wet weather returned from the 9th through the 13th, particularly across the west one-third of the state.   Mostly dry weather was the rule from the 14th through the 22nd while the remainder of the month brought frequent showers and thunderstorms.   Monthly precipitation amounts were well above normal across the northwest and southwest portions of Iowa while the driest weather occurred in central and south central Iowa, roughly along and just east of Interstate 35.   Monthly precipitation totals varied from 2.19 inches at Albia to 10.75 inches at Atlantic.  This was the second highest May rain total at Atlantic among 130 years of records at that location (May 1903 was wetter at 12.37 inches).   Excessively wet weather required some replanting of crops across western Iowa.   Nevertheless, for the state as a whole USDA NASS statistics indicate that planting progress and crop development are running a few days ahead of normal at month’s end.

Severe Weather. The relatively quiet start to the severe weather season this year continued through May.   There were a few isolated severe storms on the 9th, 11th and 13th.   Much more active weather came late in the month with severe thunderstorms reported somewhere in the state nearly every day between the 23rd and the 30th.   The most widespread severe weather event came on the night of the 25th when high winds, along with a few reports of large hail, were received from 20 counties scattered over the northern two-thirds of Iowa.

Spring Summary. Temperatures over the three spring months averaged 50.5° or 2.2° above normal while precipitation totaled 10.25 inches or 0.03 inches more than normal.   This ranks as the 26th warmest and 44th wettest spring among 144 years of state records.

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

                 2016___________________________2015_____________
                 MAY  APR  MAR  FEB  JAN  DEC  NOV  OCT  SEP  AUG
Maximum High:     65   84  135  213   29  244   85   75  130   25
Minimum High:     81   72    5   59   98   13   56   21   13  269
Maximum Low:      21   63  268  159   89  467  171   79  336   38
Minimum Low:      72   53   10   19   63    5   58   20   25  156
Maximum Precip:   92   72  124  141  156  439  316  162  150  158

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

                 2016                            2015
                 MAY   APR   MAR   FEB   JAN   DEC   NOV   OCT   SEP
High Temp Bias  -0.1   0.2   0.4   0.6   0.3   0.2   0.3   0.2   0.0
High Temp STD    2.0   2.5   2.6   2.4   2.1   2.0   2.2   1.8   1.7
Low  Temp Bias   0.2   0.2   0.3   0.2   0.2   0.1   0.2   0.1   0.0
Low  Temp STD    2.5   2.4   2.7   2.4   2.5   2.2   2.7   2.6   2.1
Precip    Bias   0.00  0.00  0.00  0.01 -0.01 -0.01 -0.00 -0.01  0.01
Precip    STD    0.17  0.11  0.09  0.07  0.27  0.14  0.14  0.08  0.26