May 2006
Midwest Overview - May, 2006
The month of May was as bizarre as they come, with a taste of each of the seasons. Unfortunately for some, winter seemed to hang on longer than welcome, which actually delayed the planting of corn and soybeans across the northern tier of the Midwest. At the end of the month, the average daily temperature departures across the region for May were generally below normal, ranging from 1-3°F below normal across Indiana, Ohio, Kentucky and Illinois, to near normal across Minnesota, Wisconsin, and portions of Michigan and Missouri (Figure 1).
Precipitation for the month was generally near average for a good portion of the Midwest, except for Iowa and northern Missouri who were drier than normal (Figure 2). The heaviest precipitation fell across eastern Wisconsin, including Lake Michigan, into lower Michigan, where precipitation totals were 150 to 200% of normal. Parts of southern Minnesota, northern Missouri, and most of Iowa saw precipitation deficits, with generally 25 to 50% of normal. The remainder of the Midwest states experienced between 75 and 125% of normal precipitation. Interestingly enough, the month of May did feature one large snowstorm which hammered northern Wisconsin and the Upper Peninsula of Michigan with up to as much as 8 inches of snow (Figure 3).
A Potpourri May
The month of May featured almost every weather phenomena known in meteorology and climatology, but it did not start out that way. Rather, May began with temperatures below average west of the Mississippi River, to above average temperatures in the Ohio Valley, but very little or sporadic precipitation episodes with only a few severe thunderstorms. The upper levels of the atmosphere featured a ridge in the west, and a trough in the east, resulting in northwesterly flow across the Midwest (Figure 4), which is typically associated with cooler and drier conditions. Embedded within this northwesterly flow was a strong shortwave trough, which barreled through the Midwest and then eventually became "cut-off" from the main jet stream (Figure 5). This resulted in a week-long spell of cloudy and wet conditions for just about each state in the Midwest. On May 12, high temperatures failed to hit 50°F across a large portion of the Midwest (Figure 6). The cut-off low also brought some extremely high winds to the Midwest, and several states recorded peak wind gusts in excess of 50mph. However, in Door County, WI, winds gusted as high as 70mph, which when combined with snow, brought down some 60' tall pine trees and snapped power lines, cutting electricity to some 30,000+ residents. Once the cyclone departed, northwesterly flow aloft continued, and cooler than normal conditions prevailed for a third consecutive week across the Midwest (Figure 7). Severe thunderstorms with large hail and heavy rain were more prominent in the third week of May than the previous two, however no major outbreaks of severe weather occurred in May. Finally, towards the end of the month, after taking a barrage of cold, snow, wind, hail, and flash flooding, the Midwest was geared up for warmer weather, and the heat made a comeback...big time. In excess of 80 new record warm temperatures were set over Memorial Day weekend across the entire Midwest, with highs approaching 100°F in central Minnesota on May 28. The warmer and more humid airmass that engulfed the Midwest during the last few days of May did allow for more numerous showers and thunderstorms, some with heavy rainfall and large hail, but there were few widespread impacts aside from the usual downed trees and power lines. In the end, residents in the Midwest during the month of May experienced drought, flash flooding, record cold, record warmth, heavy snow, high non-thunderstorm related winds, large hail, severe thunderstorms, and a few tornadoes. Indeed, a potpourri of weather from Mother Nature.
Spring 2006
The spring of 2006 will go down as a warmer than average spring, with average temperature departures running 2-4°F above normal across Minnesota and Wisconsin, and -0.5 to +1°F around normal across the Ohio Valley (Figure 8). Precipitation was largely near normal as well, ranging from 100 to 125% of normal precipitation across a wide range of the Midwest (Figure 9). Compared to the spring of 2005, which was anomalously dry, drought conditions and concerns were eased this spring by timely and generous precipitation days. These more frequent precipitation events, however, were commonly associated with strong to severe thunderstorms. While not unusual for spring in general, the early arrival of deadly supercell thunderstorms in the first days of March was a surprise. In fact, severe weather was far more common this spring than just last year, and was also above the 3-year average. According to preliminary data from the Storm Prediction Center, in the spring of 2006, the United States as a whole recorded 715 tornadoes, 77% of which came in March and April, whereas in 2005, the spring featured "only" 317 tornadoes nationwide, 61% of which occurred in March and April. Over the past three years, the spring season averages 36% of its tornadoes in March and April, and the remaining 64% occurs in May. Two of the more notable storms this spring included a tornado that moved through Springfield, IL, the capital of Illinois on March 12, 2006 (Figure 10), and another through Iowa City, IA on April 13, 2006.