October 2015
Midwest Overview - October 2015
Warm Seasonal Transistion
The Midwest experienced near-normal to above-normal average temperatures by 1 to 4°F during October (Figure 1). Average temperatures across the region ranged from 40 to 50°F across the northern one-third of the region, and 50 to 60°F across the southern two-thirds of the region (Figure 2). Iowa saw average temperatures between 50 and 55°F, and much of Missouri and all of Kentucky recorded an average temperature between 55 and 60°F. The warmer-than-normal temperatures were greatest in Minnesota, Wisconsin, and Iowa, with a southeast extension through the northern third of Illinois and eastward into much of Indiana, northwest Ohio, and south-central Michigan. Far western Minnesota recorded mean temperatures 3 to 4°F above normal. The monthly average maximum high temperatures and average minimum temperatures were roughly equivalent (1 to 3°F above normal) in influencing the near-normal to above-normal monthly average temperatures (Figure 3and Figure 4). According to preliminary data, all states experienced one of their top thirtieth warmest Octobers on record (1895-2015). Of all the states, Minnesota was the warmest in the region with a departure of 3.7°F from normal, ranking as the 17th warmest October on record for the state. This October for Kentucky ranked 29th warmest on record, and was the most near-normal state in regards to average temperatures for the month of October being above normal by 1.4°F . All other states were approximately 2°F above normal.
Rainfall Deficit across Much of the Region
October was a dry month for the Midwest. Preliminary precipitation data shows an average precipitation deficit near 1 inch for the month (Figure 5). Much of the region progressively entered drought status in the U.S. Drought Monitor. Except for east-central Minnesota, northwest Wisconsin, Kentucky, far southeast Indiana, and southwest Ohio, the Midwest was 1 to 2 inches below-normal for precipitation according to preliminary numbers. Precipitation that fell was very isolated, with minimal rainfall from extratropical systems. A large portion of rainfall across eastern Illinois, Indiana, Ohio, and Kentucky came at the end of the month, when the moisture from the remnants of Hurricane Patricia entered the area and interacted with an extratropical low pressure system moving through the region October 27th - 29th (Figure 6). One to 3 inches of rainfall was recorded during this time (Figure 7). A smaller area in southern Indiana observed at least 4 inches of rain. Patricia’s rainfall helped bring monthly percent of mean rainfall values across southeast Indiana, southwest Ohio, and most of Kentucky to 100 percent of normal (Figure 8). Northwest Wisconsin and east-central Minnesota were the only other regions recording 100 percent of normal rainfall for the month. Until October 27th, observed rainfall across the central Midwest was 0.5 inch or less. Only Minnesota and the northern half of Wisconsin and Michigan had observed more than 1 inch of rainfall. The driest region in the Midwest, until moisture from Patricia moved through, had a rainfall deficit 3 inches below normal that spread across the southern two-thirds of Missouri and across southern Illinois. A 3-inch below normal dry patch was present along the southern tip of Lake Michigan as well. These values were 10 to 50 percent of normal precipitation for October. Preliminary data shows that the driest state was Missouri, having its 16th driest October on record with rainfall 2.1 inches below normal, followed by Illinois having its 17th driest October on record with rainfall 1.93 inches below normal. Only Kentucky and Wisconsin had above-normal rainfall for the month. However, the above-normal rainfall was only 0.44 inches above normal in Kentucky (31st wettest on record) and 0.82 inches above normal in Wisconsin (18th wettest on record).
U.S. Drought Monitor
By the end of October, the percentage of area in the Midwest in abnormally dry-to-moderate drought conditions had grown from approximately 25 percent across the nine-state Midwest region to approximately 49 percent. The lack of moisture through much of the beginning of the month over the region proved beneficial to harvest conditions and planting of winter wheat.
Severe Weather
On October 23rd, conditions were favorable for the development of low-topped mini supercell thunderstorms in northwest Iowa. Six tornadoes, all ranked EF-0, were confirmed from these storms. See October Climate Watch Week 4 for more details.
-OBK-