Harry Hillaker, state climatologist with the Iowa Department of Agriculture and Land Stewardship, on December 27 released a summary of the weather in 2007. It was the fourth wettest year in the 135 years that records exist. "The totals in the following summary are only through December 27, 2007 with additional precipitation expected during the last few days of the year," he notes.
Statewide average temperature: 48.9 degrees or 1.1 degrees warmer than usual. The year 2007 ranks as the 43rd warmest year among 135 years of records, and it is the ninth warmest year among the past 10 that have averaged warmer than normal.
Statewide average precipitation: 43.19 inches or 9.11 inches greater than normal. The year 2007 ranks as fourth wettest year among 135 years of records with the only wetter years being 1993 (48.22), 1881 (44.16) and 1902 (44.04).
Highest Temperature: 103 degrees at Keokuk on August 15.
Lowest Temperature: -27 degrees at Cherokee on January 16.
Tornadoes: There were 42 recorded in Iowa in 2007 compared to an annual average of 47. So 2007 had fewer tornados than average. The most damaging tornado was an F3 storm that struck Grandview and Muscatine on June 1. Otherwise there were no other F3 storms and only five that were rated as F2's.
The top weather stories of 2007 are listed in the following chronological order:
1) Ice storm & heavy snow – February 23-26 and March 1-3. A major storm event began on the afternoon of Feb. 23 and continued into Feb. 26. A severe ice storm, with most of the accumulation coming on Feb. 24, struck central and east central Iowa where 1-2 inches of ice accumulation was common, although some ice affected most of the northeastern two-thirds of the state. Wind gusts reached as high as 50 mph. This was easily the state's most widespread damaging ice storm since March 7, 1990. Heavy snow fell in addition to the ice, especially in extreme northeast Iowa where Cresco recorded a storm total of 19.6 inches of snow.
A major blizzard struck about the northwest one-third of Iowa on March 1. Snowfall in excess of one foot was common over most of west central and northwest Iowa with official totals reaching 18 inches at Harlan. Thunderstorms produced snowfall rates of 2 to 3 inches per hour in some areas. Wind gusts of 40 to 50 mph were common on both the 1st and 2nd, with 30 to 40 mph winds continuing into March 3. Omaha's Eppley Airport reported a wind gust of 58 mph. This storm, combining with another major storm the previous week, produced widespread snow cover of 20 to 27 inches across northern Iowa. Some long power outages resulted from these two storms.
2) Mild late-March followed by April freeze – March 22-31 and April 4-13. Following a period of nearly two months of cold and very snowy weather the state experienced a very mild period of weather in late March. The temperature soared to 84 degrees at Sioux City Airport on March 26, Iowa's highest temperature for so early in the year since Des Moines reached 87 degrees on March 26, 1991. Some areas even recorded overnight lows in the 60's. The March 22-31 period was the second warmest ever recorded for that time period (behind only 1910). This extended period of mild weather set the stage for a very damaging freeze in early April.
The mild weather of late March continued into the first couple of days of April. Temperatures of 76 degrees at Lamoni and Shenandoah were recorded on the afternoon of April 2. However, the first of several impulses of very cold air moved into Iowa on April 3. A hard freeze struck all of Iowa for six consecutive days from April 4 through April 9. Even afternoon high temperatures remained below freezing in many areas on April 4 and 6. Lows dropped into the teens over all but the extreme southeast edge of the state.
Strong winds made attempts to protect tender vegetation impossible. Extensive damage was done to fruit trees and grapes with the greatest economic damage being inflicted upon the state's hay crop. The worst freeze damage was inflicted upon southern Iowa where vegetation was further along in development. The statewide average temperature for the April 4 to 13 period was the coldest ever recorded for that time period in Iowa.
3) Wet spring season – April-May. Very wet weather was the rule across the western one-half of Iowa. Guthrie Center set a new April rain record for that location with 9.24 inches. At Red Oak a total of 12.53 inches of rain fell in May. The most widespread heavy rainfall came on April 22-26 (7.28 inches at Guthrie Center) and May 5-7 (6.95 inches at Randolph) and resulted in major flooding for portions of southwestern and west central Iowa.
4) Very dry early summer – June-July. A welcome period of drier weather came to western Iowa, but stayed much longer than desired. Record low precipitation totals were recorded for some northwest Iowa locations in both June and July. Rock Valley endured 42 consecutive days without so much as 0.01 inches of rain from June 23 through August 3.
5) Record wet August – August. In what proved to be a sign of things to come, several northwest Iowa locations (Sioux Center, Hawarden and Le Mars) ended a period of 39 consecutive days without measurable rain on the first day of August. The statewide average precipitation for the month of 9.78 inches easily surpassed the previous August record of 8.24 inches set in 1993 and more than doubled the monthly normal of 4.19 inches. Only two calendar months have seen more rain (June 1947 and July 1993).
Monthly totals exceeded 19 inches at three widely separated locations (19.43 at Rathbun Dam in south central Iowa; 19.11 at Waukon in the northeast and 19.05 at Rockwell City in west central Iowa). Rathbun Dam's total was swelled by a deluge of 12.34 inches that fell on August 23-24.
6) September freeze – September 15. A freeze was recorded at 52% of the official temperature reporting sites across Iowa on the morning of September 15. Lowest temperatures were 28 degree readings at Spencer, Sheldon, Elkader, Estherville and Mason City Airport. This was the most widespread freeze recorded for so early in the fall in Iowa since September 12-13, 1902 when 64% of the state registered a freeze. Crop damage was minimal thanks to a warm growing season and reasonably timely planting.
7) Wet early October – October 1-18. A period of very wet weather brought harvest activities to a halt across Iowa in early and mid October. Record October precipitation was recorded at a large number of sites. At Red Oak 11.26 inches of rain was recorded, nearly double their previous October record. Overall this ranked as the fourth wettest October for the state as a whole.
8) Dry harvest – October 19-November 30. A much drier weather pattern began on October 19 and persisted through all of November. Preliminarily Iowa recorded its third driest November on record and fifth driest of any month. No measurable precipitation was recorded at numerous northwest Iowa locations during the month. The turn to dry weather allowed the 2007 harvest to be completed in a timely manner despite the very wet period in October.
9) Wet/snowy December – December. Very wet weather returned to Iowa in December. Major winter storms struck the state on the 1st, 8th, 10th-11th and 22nd-23rd. The worst of these storms was centered on Dec. 11 when 1-2 inches of freezing rain fell across southern and southeast Iowa. Worst hit was south central Iowa where Mount Ayr recorded 1.90 inches of rain. Retailers were chagrined to have winter storms hit the state on each of the four weekends immediately preceding Christmas. Through December 27 the statewide average precipitation stood at 2.41 inches, nearly double the December normal of 1.23 inches and the sixth highest of record for the month.