Michigan’s July weather was warmest since 1955

Hot temperatures created the warmest July since 1955 and the sixth warmest since 1895. The forecast projects cooler temperatures this week.

After several weeks of above normal temperatures in Michigan, the massive upper air ridging feature that has prolonged heatwave conditions across much of the Lower 48 states will at least temporarily give way to a troughing pattern across the northeastern USA that will bring cooler weather to the Great Lakes region.

A record-breaking July

Before moving to the forecast, it is worth mentioning some climatological highlights from the month of July. Statistically, mean temperatures averaged across the state during July 2011 were 3.7°F above normal. These temperatures mean this was the warmest July since 1955 and the sixth warmest statewide since 1895. It is interesting to note that most of the warmest Julys on record occurred during the 1930’s and 1920’s.

High temperatures during the month reached or exceeded 90°F on as many as 15 days in some southern areas of the state. The normal frequency for the whole year is typically on the order of 5 to 15 days. Total precipitation averaged statewide for the month was 2.99 inches, which is only 0.03 inch above normal, but a very poor descriptor of conditions across the state as precipitation varied greatly from north to south. The state had less than a half inch (less than 25 percent of normal) across some areas of western Upper and northwestern Lower Michigan to more than 10 inches (more than 300 percent of normal) across portions of the south. Much of the heavy rain reported in southern Lower Michigan fell in two separate heavy rain events on July 27 and 29, which abruptly ended earlier dryness but led to localized flooding.

Short- and long-term forecast

Looking ahead, a cool front moving across the state overnight Tuesday (August 9) will bring noticeably cooler temperatures and a taste of early fall weather for much of the remainder of the workweek. High pressure behind the front will lead to mostly fair and dry conditions through at least Thursday (August 11). Daytime temperatures will fall back to the 70’s, while low temperatures through Friday morning will generally be in the 50’s.

A second cool front is forecast to move from west to east across the state and region late Friday or Saturday, bringing the next chance for significant rainfall, with showers and thunderstorms possible Friday evening through Saturday evening. Fair and cooler weather is expected for the remainder of the weekend into early next week.

Latest medium range forecast guidance suggests that the upper air pattern change currently taking place across the region will persist through at least early next week, with a gradual flattening of the jet stream flow into a mostly west to east zonal pattern by late next week. NOAA Climate Prediction Center 6-10 and 8-14 day outlooks (covering August 14-18 and 16-22) both call for normal to below normal precipitation totals across Michigan. Below normal mean temperatures are forecast during the 6-10 day period moderating to near normal during the 8-14 day time frame.

Figure 1. Radar-estimated precipitation totals (top) and percent of normal precipitation
(bottom) across Michigan and the Great Lakes region, June 30 – July 29, 2011. Figures
courtesy of NOAA National Weather Service, Advanced Hydrologic Prediction Center, Silver Springs, MD.

Dr. Andresen’s work is funded in part by MSU‘s AgBioResearch.

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