fall

December 1, 2010

Warm November in Illinois

November

The statewide average temperature for November 2010 was 43.4 degrees, which was 1.6 degrees above normal. That makes it the 26th warmest November since statewide records began in 1895.
By the way, the 2000’s are well represented in the list of warm Novembers. Their rank and year include: #1 (2001), #5 (2009), #10 (2004), #14 (2003), #16 (2005), and #17 (2006).
The statewide average precipitation for November was 3.2 inches, only 0.1 inches below normal. November was exceptionally dry until the long Thanksgiving weekend arrived. Rains from that period signaled the recovery of soil moisture around the state. See the earlier posts on this subject.
The highest monthly total precipitation in Illinois for November was 7.15 inches recorded at Mt Carmel. The highest daily temperature for November was 82 degrees recorded at Cairo on November 13. The lowest daily temperature for November was 12 degrees recorded at Mt Carroll on November 26.

The statewide average temperature for fall (September-November) was 55.4 degrees, 1.2 degrees above normal.
The statewide average precipitation for fall was 8.6 inches, 0.8 inches below normal. Widespread rains in early September and late November masked the long period in between with dry conditions.
Note: these numbers are preliminary and subject to change as more data arrives.

October 12, 2010

More on Soil Temperatures in Illinois

Here are the average dates in fall when the 4-inch soil temperature falls below 50 degrees (left panel) and below 60 degrees (right panel). Consider these as a “rule of thumb” for planning purposes. Consult the current soil temperatures, as discussed in the earlier post, for decisions on applying nitrogen in the fall.

Average date when 4-inch soil temperature drops below 50 and 60 degrees. — Average date in fall when the 4-inch soil temperature drops a) below 50 degrees, and b) below 60 degrees.

October 6, 2010

Frost in Illinois

Frost is defined as ice crystals that form on a freezing surface as moist air comes in contact with it. Farmers, landscapers, and gardeners are interested in frost in both spring and fall. However, frost is usually not measured directly at weather stations. Instead, we choose dates when the air temperature crosses the threshold of 32°F.
The Midwestern Regional Climate Center keeps tabs on what places have hit 32 degrees so far this fall. Click to enlarge.

Frost Climatology

The average date ranges from October 7 in far northern Illinois to October 21 or later in far southern Illinois (see map below). The actual date varies from year to year. For tender plants in the fall, subtract two weeks from the average date to protect against an early frost.
Although 32°F is the temperature traditionally used to identify frost, visible frost can be seen on the ground and objects when temperatures are slightly above 32°F. This occurs on calm, clear nights that allow cold, dense air to collect near the ground. Under these conditions, the temperature near the ground actually can be a few degrees cooler than at the 5-foot height of the official National Weather Service thermometer.
Open, grassy areas are usually the first to experience frost, while areas under trees are more protected because the trees help prevent the heat from escaping. Homeowners can protect tender plants by providing this same type of protection if they cover their plants when a frost is expected. Plants near heated buildings sometimes are spared too. Those living in the country tend to see frost earlier in the fall than those who live in town, because of the many warm buildings and trees in town may ward off frost in some cases.

Fall Frost — Average date when temperature first drops below 32 degrees in Fall.

September 23, 2010

Fall Color

One of the best things about this time of year is the fall color. I suppose I’m hopelessly Midwestern because I even enjoy the change in color of the corn fields.
The question I often get is “How will the weather affect this year’s color?” It is hard to answer. Here are some comments I made in a press release a few years ago about the recipe for good fall color.

“Trees and shrubs need to go into the fall without a lot of stress from disease or severe drought. Chilly, not frigid nights and cool, sunny days enhance the changing leaf colors. Detrimental conditions include extended periods of rain or cloudiness that mute colors, high winds that blow leaves off trees, and hard freezes that stop color changes entirely… October and early November in Illinois should put on quite a show. Take some time to go out and enjoy it,” concludes Angel.

Check out the official site of the Illinois Office of Tourism for fall activities. The University of Illinois Extension Service site called “The Miracle of Fall” is an excellent source of information as well. [Update] NOAA has a featured story on fall color that includes a link to a more technical discussion of fall leaf color.

University of Illinois Extension site on "The Miracle of Fall".