IOWA ANNUAL WEATHER SUMMARY
2007

General Summary.   Annual temperatures averaged 48.9º or 1.1º above normal across Iowa while precipitation totaled 43.35 inches or 9.27 inches above normal.   This ranks as the 43rd warmest and 4th wettest year among 135 years of state records.   Only 1993 (48.22 inches), 1881 (44.16) and 1902 (44.04) were wetter.

Temperatures.   Unusually warm weather in March, May, August and October helped make 2007 the ninth year among the past 10 to average warmer than normal.   Annual temperature extremes varied from a low of -27º at Cherokee on January 16 to a high of 103º at Keokuk on August 15th.   The 2007 air conditioning season averaged 11% warmer than 2006 and 20% warmer than normal, as estimated by cooling degree day totals.   This was the warmest air conditioning season since 1991, although only a fraction of a percent warmer than 2002 and 2005.   Nevertheless, triple digit heat was restricted to only Van Buren and Lee Counties.   Thus summer heat was more persistent than extreme.   However, the two most notable temperature extremes of the year were on the cold end of the spectrum.   A series of very hard freezes struck the state each day from April 4 to 9, resulting in severe damage to many horticultural crops, as well as to hay.   Temperatures fell into the teens over all but extreme southeast Iowa.   Freeze damage was greatest in southern Iowa where vegetation was further along in development.   Another unusual freeze came on September 15.   This event brought a freeze to 52% of the state and was the earliest widespread freeze in Iowa since September 12-13, 1902 when 64% of the state was struck.   However, unlike the April freeze, crop damage was minimal as temperatures were not as extreme (lowest temperature of 28º) and crops were well advanced in maturity thanks to a warm growing season.

Precipitation.   Very wet weather was frequent throughout the year.   Record high monthly precipitation totals were recorded at some Iowa locations in April, May, August, October and December.   April and May were especially wet in southwestern Iowa with severe flooding in some areas in early May.   August was by far the wettest month.   The statewide average precipitation of 9.78 inches was an inch and one-half greater than the previous August record set in 1993.   In fact only two months have ever been wetter (July 1993 at 10.50 inches and June 1947 with 10.33).   August rainfall exceeded a foot and a half at locations scattered across northwest, northeast and south central Iowa.   October was particularly wet in southwest Iowa while December was very wet across the south and east.   Meanwhile two periods of very dry weather also were experienced.   The first affected mainly northwestern Iowa in June and July with record low monthly rain totals recorded in some areas.   Good soil moisture reserves from earlier wet weather and the lack of excessive heat apparently prevented major yield reductions for crops.   The second dry period came in late October and persisted through November for all of the state.   This dry period was very welcome and allowed harvest activities to be completed in a timely manner despite extremely wet weather in early and mid October.   Annual precipitation totals varied from 26.58 inches at Rock Rapids to 56.80 inches at Guthrie Center.   Guthrie Center, Waukon and Lansing all recorded their wettest year in 2007 with precipitation more than 20 inches greater than normal.   Only 3 of 162 measurement sites received less than normal annual precipitation (Rock Rapids, Fort Madison and Keokuk).

Snowfall.   It was a very active year for winter storms in 2007.   Snow and ice was frequent from mid January through early March and again in December.   Of particular note was a major ice storm, centered on February 24, which brought ice to much of the northeastern two-thirds of the state.   Ice accumulations of one to two inches were common in central and east central Iowa with major damage to trees and power lines.   Northern fringes of the storm saw heavy snowfall with 19.6 inches at Cresco.   Less than a week later a major blizzard struck northwest Iowa on March 1 with snowfall amounts reaching 18 inches at Harlan.   Thunderstorms resulted in snowfall rates of 2 to 3 inches per hour in west central Iowa while wind gusts of 40 to 50 mph were common.   On December 1 a winter storm brought significant freezing rain to much of Iowa.   Another ice storm struck the southeastern one-half of the state on December 11.   This storm was accompanied by lower temperatures than the Dec. 1 event and brought ice accumulations of one to two inches from south central to east central Iowa.   Major power outages resulted from the ice despite the lack of high winds with this storm.   Overall the state saw an average of 46.9 inches of snow, 14.5 inches more than normal, and the 8th greatest annual total among 120 years of state snow records.   Lansing, in the extreme northeast corner of the state, recorded 80.5 inches of snow for the year.

Severe Weather.   A total of 42 tornadoes were reported during the year, slightly less than the annual average of 47.   The most damaging storm was an F3 tornado that struck Grandview and Muscatine on June 1.   This was the year’s only F3 event, with another five F2 storms.