Biology

As the hot, dry summer of 2012 gives way to the arrival of autumn this weekend, WKU meteorology faculty member Gregory Goodrich in the Department of Geography and Geology prepared the following report for the Kentucky Climate Center:

Summer 2012 recap

Following the wettest year in Kentucky history in 2011, the summer of 2012 in southcentral Kentucky brought a severe drought and a record-breaking heat wave of the type not seen since the Dust Bowl years.

After a nearly snowless winter and a historically warm spring, southcentral Kentucky began to experience mild levels of drought at the start of summer. A record-breaking heat wave that began in late June and continued into July deepened the drought to “severe” status in Bowling Green while the western third of the state suffered through “exceptional” drought, creating drought conditions not seen in some cases since the 1930s.

• The extremely dry soils allowed temperatures to soar to 110 on June 29 in Bowling Green, which was the second highest temperature ever recorded there on any day.
• The four-day period from June 28 to July 1 had high temperatures of at least 105 each day, which had only happened one other time in Bowling Green history (Aug. 6-9, 1930).
• An 11-day stretch from June 28 to July 8 had high temperatures of at least 98, which was tied for the second longest stretch of such days in history (both 1918 and 1936 had 14-day streaks).
• The four days of 105+ weather this summer was one more than the total number of 105+ days in the last 60 years (two in 1980, one in 2007). However, this pales in comparison to the 1930s, when 105+ weather happened 24 times.
• Most residents of southcentral Kentucky would be surprised to know that the summer of 2012 only ranked as the 14^th warmest summer in Bowling Green since 1893 and was less hot than the recent summers of 2007, 2010 and 2011.
• While the last three days of June and nearly all of July were scorchingly hot, the first 27 days of June were actually slightly cooler than normal and August was also normal.
• Recent rainfall in the first few weeks of September has effectively ended the drought across southcentral Kentucky, although the western third of the state is still experiencing severe drought.
• The extensive drought in western Kentucky reduced corn yields by over 50 percent in some areas, leading some farmers to plow their fields under.

The meteorological conditions that contributed to the record temperatures and extremely dry weather are identical to those in 2011 that contributed to the record rainfall.  For the second consecutive year, La Niña conditions in the Pacific Ocean have been paired with the cold phase of the Pacific Decadal Oscillation (PDO).

The second year of multi-year La Niña events that occur in tandem with the cold phase of the PDO are commonly associated with extensive drought in Kentucky, as was the case in 1999-2000 and in the early 1950s. In this case, the La Niña that developed in 2011 produced a dome of high pressure over the central Plains that contributed to record-breaking heat and drought in that region. In 2012, the dome of high pressure expanded to the east, which cut off the moisture supply from the Gulf of Mexico and led to the warm temperatures and drought conditions across Kentucky.

Fall/winter outlook

With El Niño conditions expected to develop in the fall, the expectation is that drought conditions across Kentucky will be improved over the next several months, although El Niño winters can be highly variable across Kentucky depending on their strength.

In recent years, moderate to strong El Niños like those that occurred in 1997-98, 2002-03 and 2009-10 have often been colder than normal with well-above average snowfall while weaker El Niños like those in 2004-05 and 2006-07 were mild with little snowfall.

Computer models project that the upcoming El Niño will be weak, although this can change as winter approaches.

More: For additional information/updates on weather and climate, visit the Kentucky Climate Center, Kentucky Mesonet, WKU Meteorology Blog or WKU Storm Toppers.

Contact: Greg Goodrich, (270) 745-5986.