The combination of several rounds of widespread moderate to locally heavy rains, and even melting snow, during the month produced strong within bank rises to minor flooding on most of the tributary rivers across the HSA. The runoff from May, along with rain and snowmelt runoff from April moving down the channel, produced a full within-bank rise of 6 to 9 feet to minor flooding on the Mississippi River from Lake City MN to Guttenberg IA.
Precipitation for May 2013 ranged from above normal across the east and southeast ends of the HSA to much above normal and excessive across the remainder of the HSA. A strong and slow moving low brought widespread moderate to heavy precipitation to the HSA from the 1st to the 3rd, heaviest over the northwest half. The next passing low brought widespread moderate to locally heavy rain to the HSA on the 9th. Spotty light showers occurred from the 10th to the 16th. Two more strong lows brought moderate to heavy rain to the HSA from the 17th to the 20th, again heaviest over the northwest half. A lingering low and weaker system brought showers with light to moderate rains to the HSA from the 21st to the 26th. To end the month, a series of slow moving systems brought light to locally heavy rains to the HSA from the 27th to the 31st, heaviest across the central and northwest portions of the HSA. The heavy rains from the 17th to the 20th and from the 29th to the 31st produced the strong with bank rises and minor flooding on the tributary rivers on the 20th-21st and 30th-31st
Normal May rainfall ranges from around 3.5 inches across the northeast half of the HSA, to near 4.5 inches across the northeast IA portion of the HSA. Totals for the month ranged from 125 to 150 percent of normal across the east and southeast ends of the HSA, to 300 to 400 percent of normal over portions of northeast IA and southeast MN. Most May totals were 200 to 300 percent of normal. Extreme totals recorded for the month ranged from 4.62 inches at Cuba City in southern Grant Co. WI and 4.97 inches at Friendship in Adams Co. WI, to 12.71 inches west of Altura in Winona Co. MN and 14.64 inches at Grand Meadow in Mower Co. MN. A strong and cold late season storm brought record snowfall to portions of the HSA on the 2nd into the 3rd. Snowfalls of as much as 4 to 17 inches fell across the northwest 1/3 to half of the HSA, breaking records for the most snow in May and on a single day in May. Statewide records for most snow on a single day were set in both MN and IA. Normal May snowfall across the HSA ranges from zero to a few tenths of an inch.
May 2013 temperatures averaged 56 to 59 degrees. This was 2 degrees above to 2 degrees below the normals. Temperatures were below to much below normal on the 1st to the 4th, below normal from the 9th to the 13th and from the 22nd to the 28th. Temperatures were near to much above normal from the 5th to the 8th and 14th to the 21st, then above normal from the 29th to 31st. Extremes for the month ranged from lows in the middle 20s to lower 30s on the mornings of the 2nd and 3rd, to highs in the 80s northeast of I-94 to the upper 90s across the west end of the HSA on the 14th.
Flows in the rivers and streams of the HSA were above to much above normal during May. By the end May Soil conditions were excessively wet across much of the HSA, a full reversal from the drought conditions of summer and autumn of 2012. These wet conditions continued to delay spring field work and planting activities, with progress as much as 3 to 4 weeks behind normal. Many acres will likely not get planted for the 2013 season.