Pat Guinan
State Climatologist
Commercial Agriculture/University of Missouri Extension

Temperatures during the 2010 growing season were in stark contrast to the previous two years with every month this year, from April through October, averaging above normal. Specifically, the April through October periods in 2008 and 2009 were cool, averaging 1.1 and 2.1 degrees below normal, respectively. Alternatively, preliminary data are indicating this year's growing season was the warmest in Missouri since 1963. This year was also a year of precipitation extremes ranging from flood to drought across the Show Me State.

The spring of 2010 will go down as a seasonably wet and mild one for Missouri. April and May were warmer than normal averaging 5.7 and 0.7 degrees Fahrenheit above normal, respectively. Three weeks of mild weather during April made it the fifth warmest April on record for Missouri, and two consecutive months with above normal temperatures translated to the 10th warmest April-May period out of the past 116 years. The mild spring followed the seasonal trend over the past decade with 7 out the past 10 springs being warmer than normal.

Generally, the last spring frost this year occurred 1 to 2 weeks earlier than normal with most northern locations experiencing their last =32°F on 4/8 or 4/9 and central and southern sections during the last week of March. Some low-lying areas along the Ozark Plateau witnessed freezing temperatures as late as mid-April whereas the Bootheel counties saw their last frost during the first week of March, nearly 4 weeks earlier than normal.

A weather pattern shift in May led to a more seasonable to below-normal temperature regime during the first 3 weeks of the month with several days of cool, cloudy and damp conditions occurring during mid-month. The pattern abruptly shifted to much warmer and drier weather during the last 10 days of May with many locations reporting daily maximum temperatures well into the 80s and lower 90s through the end of the month. Some daily record high temperatures were also established during this time.

Springtime precipitation was variable across the state from month to month, but statewide average precipitation for April totaled 3.50 inches and was slightly below normal. May rainfall was heavier and averaged 6.79 inches, or more than 2-inches above normal. The combined April-May average was 10.29 inches, which is 1.43 inches above the seasonal norm.

Regionally, precipitation extremes for April ranged from 5.5-8.5 inches over central and northeastern sections to less than 3 inches in parts of southwestern Missouri. May high rainfall extremes ranged from 8-11 inches across southwestern sections and a few northern Missouri counties, especially along the Iowa border. Alternatively, the lowest May rainfall totals ranged between 3-5 inches over portions of east central and southeastern Missouri.

The seasonably warm and wet spring conditions transitioned to a hot and humid summer across all of the Show Me State. Official weather station records indicate it was the hottest summer in 30 years with varying amounts of precipitation, ranging from excess to drought.

June, July and August were all warmer than normal averaging 4.4, 1.6 and 3.3°F above normal, respectively. Overall, the average summer temperature was 78.4°F degrees, or 3.1 degrees above normal. Three consecutive months of above normal temperatures resulted in this summer being the 9th hottest in the past 116 years and the hottest since 1980. Individually, June, July and August ranked as the 8th warmest, 19th warmest and 15th warmest on record, respectively.

Some notable characteristics of this summer were unusually high dewpoint temperatures, which translated to extended periods of above normal minimum temperatures. For example, preliminary data indicated the average dewpoint temperature in Columbia, MO this summer was 69.0°F, which makes it the highest on record when comparing to dewpoint observations since 1948. The second highest average summer dewpoint temperature for Columbia was 68.9°F in 1995.

Additionally, Columbia experienced only 12 days during the 3-month period when minimum temperatures fell below normal. The average minimum temperature for Columbia was 68.3°F, or 4.3° above normal, whereas the average maximum temperature was 87.5°F, or 0.9° above normal. These air temperatures, in combination with unusually high dewpoint temperatures, led to several uncomfortable days and extended periods of high heat indices that have not been seen in more than a decade.

The heat was more intense across southern sections of the state where drought conditions evolved and persisted for much of the summer, especially across southeastern sections. Some communities in the Bootheel experienced 10 days with triple digit heat this summer and 69 days with temperatures = 90°F. Preliminary temperature observations from the Bootheel indicated it was their 3rd hottest summer on record and the hottest since 1936.

Summertime rainfall was variable across the state from month to month, but overall, statewide average precipitation for June and July totaled 4.59 and 6.59 inches, respectively, and was above normal for both months. August rain events were infrequent and averaged 2.35 inches, or just over 1-inch below normal. The combined summertime average was 13.53 inches, which is 1.74 inches above the statewide seasonal norm.

Regionally, precipitation extremes for June ranged from 8-12 inches across northern Missouri to less than 1-inch over portions of southeastern Missouri. The community of Kahoka, in far northeastern Missouri, reported 14.36 inches for June whereas the town of Bloomfield, in southeastern Missouri, reported no measureable rainfall during the entire month of June.

July extremes varied from 7-12 inches over much of central and northeastern Missouri to less than 3 inches in some southeastern communities. Hannibal reported their 2nd wettest July on record with a whopping 17.26 inches. Statewide, the month ranked as the 8th wettest July on record.

Drier conditions prevailed in August with extended periods of no rainfall and abundant sunshine. Southern sections of the state experienced the driest conditions where generally less than 2-inches of precipitation were reported. Caruthersville, MO reported no precipitation for the entire month. Localized dryness was also reported in some northwestern counties. Heaviest August rainfall occurred over central sections where 3.5-5.0 inches were common.

Overall, June through August rainfall totals ranged from more than 25 inches in northeastern sections to less than 4 inches over parts of the Missouri Bootheel. Kahoka, MO reported 29.10 inches for the summer, whereas a paltry 3.10 inches was observed in the Bootheel community of Kennett, MO.

Statewide average temperatures in September were slightly less than one degree above normal. Regionally, seasonably mild conditions were dominant over central and southern sections where monthly average temperatures ranged 1 to 1.5° above normal. Northern portions of the state experienced near normal monthly temperatures ranging from slightly below normal to about 0.5° above normal. There were no extended hot periods during the month and only a handful of days when a few locations reported temperatures in the lower 90's.

Rainfall was nearly 4 inches above normal for the monthly with preliminary data indicating a statewide average of 8.46 inches. It was the 5th wettest September on record and the wettest September since 1993. All areas of the state experienced above normal rainfall with the exception of the Bootheel, which averaged less than 3 inches. A few counties in southwestern Missouri reported more than 14 inches of rain for the month. Alternatively, two Bootheel locations, Kennett and Caruthersville, reported less than 1-inch for the entire month.

Dry and mild conditions emerged statewide during October and allowed crop harvest to rapidly progress. As of October 24, the corn and soybean harvest were running well ahead of normal at 90% and 79% complete, respectively. Winter wheat planting was nearly 2 weeks ahead of schedule at 74% complete. Even though the dry weather provided excellent harvesting opportunities, there were concerns of lack of moisture for winter wheat to germinate as well as continued widespread poor pasture conditions in south central and southeastern sections of the state. Lingering impacts of summer drought and continued fall dryness led to substantial pasture yield loss across much of south central and southeastern Missouri and many farmers were already feeding hay.

Statewide October rainfall was well below normal and preliminary data were indicating it ranked as the 4th driest October on record and the driest since 1964. The average statewide total was 0.70 inches, which is 2.66 inches below normal. The growing season effectively came to an end across much of the Show Me State on the morning of October 29 when widespread freezing temperatures occurred for the first time across much of the Show Me State.