Unseasonably cool and wet weather dominated the weather scene across central, east central and southeast Illinois this past October. Both Peoria and Springfield averaged around 4 degrees below normal for the month with precipitation at Peoria 5.18 inches above normal while Springfield was 8.70 inches above normal for October 2009, the second wettest October on record! As of November 1st, 2009, precipitation at Peoria totaled 47.45 inches, 16.81 inches above normal for the year. Springfield's precipitation total as of November 1st was 44.69 inches, 14.54 inches above normal.
Central Illinois had several major rain events across the area during the month, the first of which occurred on the 8th which is illustrated in Figure 1 below. Low pressure moved out of the southern plains and interacted with deep tropical moisture resulting in a swath of moderate to locally heavy rainfall affecting areas along and south of Interstate 72. As that system pushed off to our east, cold high pressure built in from the Canadian Rockies producing frost and some freezing conditions across parts of central Illinois on the mornings of the 10th and 11th, with the coldest temperatures affecting areas north of Interstate 74. Our first reports of snow (flurries) came in during the evening of the 11th with flurries reported in Lincoln and just west of Peoria. During the period of October 12th through the 19th, very chilly air settled in with several locations either tying or breaking record low maximums. On October 15th, Peoria tied its record low max with a daytime high of only 43 degrees, with many areas across the north staying in the low to mid 40s for afternoon highs, some 20 to 25 degrees below normal.
As the cold fair weather system pushed off to our east, another in a series of weather disturbances developed across the southern plains and pushed across the region during the 3rd and 4th weeks of the month bringing two rounds of heavy rainfall, this time affecting areas further north than the first system back on the 8th. As was the case with the earlier systems, the area of low pressure which affected central Illinois at the end of the month originated over the southern plains where it had plenty of time to spread deep tropical moisture northward into our area, resulting in a band of 2 to 3 inches of rain pushing northeast and affecting areas north of Interstate 72, with reports out of central McLean county receiving 3.10 inches of rain on the 29th and 30th, the second rainfall system that produced over 3 inches in McLean county during the past week to 10 days.
Figure 2 (SWOP rainfall reports from the 29th/30th)
Needless to say, with all this rain which occurred across central, east central and southeast Illinois, the water had to go somewhere and it did, into our rivers and streams. Significant rises were seen at the end of the month with all the forecast points along the Illinois River (Henry, Peoria, Havana and Beardstown) at or going into flood. Further south and east, flooding was observed along the Sangamon and Mackinaw rivers. Across southeast Illinois, the Little Wabash river at Clay City experienced minor flooding due to the significant runoff from the heavy rainfall.
For a more detailed look at the climate stats across the area for the month of October, click on the links below.