Historic Wetness in Missouri During 2008

Pat Guinan
State Climatologist
Commercial Agriculture/University of Missouri Extension

The heavy precipitation event that impacted Missouri during the last weekend of the year couldn't have been more representative of the weather theme for the Show-Me state during 2008. Persistent wetness and significant flooding was the recurring theme across much of Missouri and, by the end of the year, preliminary numbers were indicating it to be the wettest year on record, barely eclipsing the historic wetness that occurred in 1993. Average statewide precipitation in 1993 was 56.90 inches making it the wettest year on record, until now. Current estimates are indicating average precipitation in December 2008 was just over 3 inches which, when annual numbers are totaled, will give an average statewide total precipitation for Missouri of just over 57 inches, barely exceeding the 1993 watermark.

The historic wetness this year began to evolve in February 2008 when an unsettled weather pattern established itself across the lower Missouri River Valley. A contributing factor to the stormy winter was a moderate La Niņa event, a phenomenon of cooler than normal sea surface temperatures in the Equatorial Pacific. La Niņa and other atmospheric factors sustained a dynamic jet stream that extended from New Mexico to Michigan and led to numerous winter precipitation events across the region. Even though La Niņa weakened in the spring, and transitioned to a neutral condition during the summer, the unsettled weather pattern persisted with above normal precipitation impacting Missouri for six consecutive months beginning last February. Notably, there were 6 extreme flood events in 2008 with the first one impacting southern and east central Missouri on March 18-19. Many locations south and east of the I-44 corridor received 3 to 8 inches of rain with Cape Girardeau breaking an all-time official daily and monthly record of 11.49 inches and 17.84 inches, respectively.

Planting opportunities were limited as the cool and wet conditions persisted throughout spring. Fieldwork activities were interrupted by significant rain events frequently occurring across the state. Columbia, MO typically records 33 days with measurable precipitation between April and June, but, in 2008, there were 50 days with measurable rainfall. During much of June, historic flooding was impacting the Mississippi River and a major rain event struck northern Missouri during the last week of June. On June 24-25, 3-8 inches of rain fell along a corridor from Chillicothe to Hannibal that resulted in major flooding, especially along the Grand, Thompson and Chariton Rivers.

Exactly one month later, on July 24-25, another extreme rain event struck north central Missouri with 6-12 inches centered on a line extending from Unionville to Kirksville to Macon to Moberly. Many locations witnessed 1 in 100 year 24-hour rainfall events with Kirksville setting an all-time official 24-hour rainfall record and monthly record for July with 7.67 inches and 15.13 inches, respectively. Other reports from the Kirksville area ranged from 10-12 inches. Once again, extensive flooding was reported with record crests occurring along portions of the Thompson and Chariton Rivers.

Other significant contributors to 2008 precipitation totals across the state were remnants of tropical systems. An unprecedented five systems impacted Missouri and were associated with the remnants of three hurricanes (Dolly, Gustav and Ike) and 2 tropical storms (Fay and Lowell). Gustav, Lowell and Ike were the biggest contributors resulting in 5-10 inches of rain across much of the state during the first half of September. Extensive flooding was again reported over an already saturated state.

Fortunately, a respite from the extreme wetness occurred during October and November with statewide precipitation averaging below normal for both months. Drier conditions resulted in decent harvesting opportunities but another wet regime emerged in December. During the last weekend of the year, a storm system dropped 1-2 inches of rain across the state and likely tipped the scale for 2008 to become the wettest year on record.

Missouri had the dubious distinction of having the largest above normal departures for any state in the U.S. during 2008, averaging more than 16 inches above normal for the year. Most locations reported than 50 inches of rain with many counties receiving more than 60 inches and a handful of stations reported more than 70 inches. The heaviest statewide official total for the year resides in the northern community of Unionville, MO, in Putnam county. Unionville reported a whopping 73.96 inches of precipitation in 2008, nearly double their annual normal of 37.26 inches. Indeed, it was an incredible, and unprecedented, year in regard to wetness.