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Monthly Overview - October 2017

Shift to Wetter Conditions for Most of Midwest

October was wetter than normal for much of the Midwest following a September with mostly below normal rainfall (Figure 1). Only southeastern Missouri and northwestern Minnesota had 75% or less of normal precipitation during the month. On the other hand, all nine states had areas with 150% or more of normal and all but Kentucky and Ohio had areas with more than 200% of normal (Figure 2). Large swaths of Iowa, Michigan, southern Minnesota, and northern Illinois had more than twice their normal precipitation for the month. Statewide precipitation numbers ranged from 102% of normal in Missouri to 200% of normal in Iowa and 207% of normal in Michigan. More than 680 daily records were set in October with all nine states having at least a couple dozen new records. Iowa, Illinois, and Michigan each had over 100 daily precipitation records set in October.

Warm, then a Cold End to the Month

Temperatures averaged over October ranged from near-normal in parts of Minnesota and Iowa to as much as 5°F above normal in parts of Michigan and Ohio (Figure 3). Much of October had warmer than normal temperatures, but temperatures fell sharply in the last few days of October spreading freezing conditions across the Midwest. Nearly all of the daily record low temperatures came in the last four days of the month while record high temperatures were spread across the first 3+ weeks of the month. The number of record highs (475) wasn't significantly higher than the number of record lows (337) and all nine states had both types of records in October. Maximum temperatures reached at least 80°F in all nine states, and topped 90°F in several Missouri stations. Minimum temperatures dropped to 20°F or less in every state except Ohio where temperatures reached the mid 20s. Statewide temperatures for October were at least 2°F above normal in all of the Midwest states with Michigan at 4.9°F above normal.

Drought Eases Except in Missouri

Drought conditions improved or were eliminated in many parts of the Midwest, but Missouri saw the opposite with expansion and degradation. As of October 3rd, nearly half of the region was either abnormally dry or in drought with nearly 12% of the region in drought. (Figure 4) By the October 31st release of the US Drought Monitor, those numbers shrank to under a quarter of the region abnormally dry or in drought with about 7% in drought. Stream flows also increased in much of the Midwest from the 1st (Figure 5) to the 31st (Figure 6).

Rains Slowed Corn Harvest

Harvest progress was slowed by rainy conditions in October. As of the October 29th NASS Crop Progress, reports of corn harvest ranged from within a couple percentage points of the 5-year average in Kentucky and Michigan to 25% or more behind the 5-year average in Iowa, Minnesota, and Wisconsin. Soybean harvest numbers were much closer to the 5-year averages, with all nine states within 10% of the average for the end of October.

First Freeze

The first freeze of the season came in October for the vast majority of the Midwest (Figure 7). A few northern stations had a freeze in September and a few stations, mostly near the Great Lakes or along the Ohio River, made it through October without dropping to freezing. Median first freeze dates (Figure 8) showed the first freeze was later than average in nearly all of the Midwest by a week or two.

First Snow of Season

The first measurable snow of the season in the Midwest fell in northern Minnesota, extreme northern Wisconsin, and in the Upper Peninsula of Michigan (Figure 9). Snow began on the 26th in Minnesota and spread eastward with lake enhanced snow along the southern shore of Lake Superior. Snow totals topped a foot at several locations, mostly in the two western-most counties of the Upper Peninsula.

The Iowa Climatology Bureau also contributed to this report.
The Minnesota State Climatology Office also contributed to this report.