May 2018
Monthly Overview - May 2018
Record Warmth
Following the 2nd coolest April on record (1895-2018 period) in the Midwest, May went the other direction and did it one better. May 2018 was the warmest on record for the region as a whole. Regionwide temperatures swung from just 40.8°F in April (Figure 1) to 66.3°F in May (Figure 2). The May temperature was 6.9°F above normal. The 25.5°F change from April to May was more than double the normal increase of 10.4°F and eclipsed the old record of 19.9°F, set in 1936, by a wide margin. Statewide values for May also set new records in Illinois, Indiana, Kentucky, Missouri, and Ohio while the remaining four states ranked among the five warmest in their respective histories
(Figure 3). New monthly records were also set at 175 stations (Figure 4), including multiple stations in all nine Midwest states. Daily temperature records also fell in bunches during May. More than 2000 daily records were tied or set in May, with state totals ranging from 145 in Kentucky to 325 in Missouri. May temperatures
(Figure 5) ranged from about 5°F above normal along the northern edge of the region to nearly 10°F above normal in a swath that stretched from northern Missouri to southern Ohio.
Mostly Drier Than Normal
May precipitation totals ranged widely from less than an inch in west central Minnesota to more than 10 inches in southern Wisconsin (Figure 6). Most of the region was below normal with two areas reporting totals that fell 2 inches short of normal, northern Missouri and an area including central Indiana and part of Illinois
(Figure 7). Much of central Minnesota reported an inch or more below normal. Areas with rainfall of 2.00 or more inches above normal in May extended along the Iowa-Minnesota border and eastward through southern Wisconsin, northeastern Illinois, and southern Michigan. Viewed as a percentage of normal (Figure 8), totals ranged from less than 50 percent of normal to more than 200 percent of normal.
Corn and Soybean Planting
Cold and wet conditions in April put many farmers behind the 5-year average for planting early in the season. When the warmer and drier conditions allowed them into the fields in late April or May, they made up for lost time and mostly caught back up to the 5-year averages. Michigan farmers were still running about a week behind in corn planting by the end of May, but much of the rest of the region had caught up by that time.
Spring Temperatures Near Normal on Average
Temperatures in April and May were both extreme, cold and then warm, but when averaged for the season largely offset each other. Spring temperatures were within a degree or two of normal for nearly all of the region. Some areas in the northern parts of the region had averages that fell just more then 2°F below normal. Nearly all of the southern half of the region fell within 1°F of normal
(Figure 9).
Spring Rains Vary
Spring precipitation (Figure 10) varied across the region with alternating dry and wet swatch extending west to east
(Figure 11). The northernmost areas were mostly dry. Another dry swath included the southern two-thirds of Iowa, the northwestern two-thirds of Missouri, and much of Illinois and Indiana. The largest deficits from normal were in northern Missouri and extreme southern Iowa with deficits of 4 inches, while a smaller area in northwestern Missouri had deficits of more than 6 inches. This area in northwestern Missouri was classified as in severe drought by the end of May (Figure 12). Wetter than normal areas included the southernmost and easternmost areas along with a swath that extended along the Iowa-Minnesota border, through southern Wisconsin, and into much of lower Michigan.
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