Heavy Rains Alleviate Illinois Drought

Heavy rains over the weekend put a major dent in the drought in southern Illinois and neighboring states. Amounts of two to four and a half inches were common throughout the southern half of the state. Some places saw more rain in the last week than in the last three months. For example, Mt Carmel reported 5.07 inches in the last 7 days while receiving a combined total of only 4.34 inches during the months of August, September, and October.

These widespread rains should give relief to other drought-stricken areas of the Midwest as well, including Missouri, Kentucky, Indiana, and Ohio.

7 day rainfall Midwest
The 7-day rainfall total for the Midwest, ending on November 28, 2010.

Much Needed Rain Arrives in Illinois

Much needed rain arrived in Illinois over the last few days. As the map below shows, amounts of 0.50 inches or higher occurred across Illinois for the 7-day period ending November 23. And typical to these situations, the area in most need of rain misses out. In this case, that would be far southern Illinois.  There is a second opportunity for rain in the next few days.

7-day rainfall
The 7-day rainfall for Illinois, ending November 23, 2010 (courtesy NWS).

Tornadoes Strike Illinois in November

Severe weather, including   four tornado reports, struck northern Illinois on November 23, 2010. According to NOAA’s Storm Prediction Center:

  • a tornado was spotted 4 miles east of Loves Park (Boone County); power lines down and debris were reported;
  • a second tornado report from 3 miles east of Loves Park (probably the same tornado) caused 3 injuries, nearly destroyed one business, and damaged other homes and a garage;
  • a tornado was spotted on the ground 2 miles northwest of Harvard (McHenry County); no damage was reported;
  • a tornado was spotted in McHenry County, right on the Illinois-Wisconsin line, 5 miles southeast of Walworth WI; apparently all the damage occurred in Wisconsin.

Besides tornadoes, high winds caused extensive damage including tree limbs and power lines down, damage to buildings, and trucks blown over. The link to the full report is here.

The NWS offices at Davenport IA and Chicago IL are conducting damage surveys. Results will be posted here:

Average Date of First Snow in Illinois

Besides the cold temperatures, one of the initial signs of winter is that first snowfall. Parts of Iowa, Wisconsin, and Indiana have already seen their first snow. In the figure below are the median dates of the first measurable snowfall (greater than or equal to a tenth of an inch) of the season in Illinois.

Think of the median date as the date by which we have seen snow in 50 percent of the cases during the period between 1971 and 2000.

In northern Illinois, the first snowfall occurs around Thanksgiving. In far southern Illinois, you have to wait until sometime in mid-December.

In about 10 percent of the cases, the first measurable snow can occur as early as November 5 in northern Illinois to November 20 in far southern Illinois.

date of first snow
The median date of the first measurable snow of the season base on 1971-2000 data (click to enlarge).

Updated Forecast for December and Winter

NOAA’s Climate Prediction Center has come out with a new forecast for December and for December-February (winter). This is part of their routine update cycle.

December

The outlook for December in Illinois calls for an increased chance of above normal temperatures.  An increased chance of above normal temperatures translates into just a few degrees above normal. Temperatures in Illinois have run an average of 2.9 degrees above normal for every month since March of this year. Therefore, continuing with a forecast for above-normal temperatures is not surprising.

The outlook calls for equal chances of above, below, or near-normal precipitation (or equal chances as they call it) in December in Illinois.

December-February (winter)

The outlook for December-February remains the same as last month. There is an increased chance of above-normal precipitation for all of Illinois. And, there is an increased chance of above-normal temperatures for the southern two-thirds of the state. See the figure below for more details.

CPC forecast
NOAA's Climate Prediction Center forecast for December and December-February (click to enlarge).