October Is Warm and Dry

So far, October in Illinois has been both warmer and drier than normal. As of October 19, the statewide average temperature was 59.8 degrees, 1 degree warmer than normal. The statewide average rainfall was only 0.22 inches, 12 percent of normal. See table below.
If this were July, the dryness would be a major source of concern. However, the impacts are much less in fall. In fact, the warm, dry weather aided in the maturing and harvesting of corn and soybeans. At the moment, the impacts are mostly focused on:

  • winter wheat – farmers are waiting on rains for germination;
  • landscaping – trees and shrubs may need more water before winter arrives;
  • fall color – I’ve noticed that the fall colors on trees and shrubs this year are muted with lots of shades of brown and yellow.

The NWS forecast shows a weather system moving through Illinois over the weekend. The potential rainfall amounts from this system range from 0.25 inches along the Wabash River in south-eastern Illinois to 1.25 inches in north-central Illinois. Another system is expected to move into the region on Tuesday/Wednesday. So the current dry weather may be short-lived.

                        10/01/2010 to 10/19/2010
Climate          <------Temperature----->   <---------Precipitation--------->
Division         Actual   Normal      Dev   Actual   Normal     Dev   Percent
Northwest          55.2     53.4      1.9     0.09     1.82    -1.73        5
Northeast          55.8     53.7      2.0     0.27     1.82    -1.56       15
West               57.6     56.3      1.4     0.10     1.90    -1.80        5
Central            56.7     55.7      1.0     0.22     1.86    -1.64       12
East               56.0     55.4      0.6     0.38     1.86    -1.48       20
West-southwest     58.0     57.5      0.5     0.13     1.72    -1.60        7
East-southeast     58.4     57.8      0.6     0.28     1.92    -1.65       14
Southwest          58.9     58.9      0.0     0.23     1.85    -1.63       12
Southeast          59.8     59.2      0.6     0.35     1.84    -1.49       19
State              57.3     56.3      1.0     0.22     1.84    -1.62       12
Dev means Deviation From Normal, Percent means Percent of Normal

October Temperature Swings in Chicago

Like most sites in Illinois, Chicago has experienced large temperature swings in October. The month started with below-normal temperatures on October 2-5. The departures were as large as 8 degrees below normal on October 3 and 4.
This cold period was followed by a period of much above normal temperatures on October 6-12. The departures were as large as 16 degrees above normal on October 9 and 10. In fact, the high of 86 degrees reported at O’Hare on October 9 tied the record set in 1962.
Slightly above-normal temperatures prevailed on October 13-18. The early cold period and later warm periods resulted in an average of 58.7 degrees for the first 18 days in Chicago, 3.9 degrees above normal.

chicago daily data october 2010
Day by day temperature departures from normal for Chicago Illinois in October 2010.


Dry Conditions Persist in Illinois

Parts of southern and eastern Illinois have struggled with dry conditions since July/August. Those conditions have expanded in recent weeks across more of Illinois.  The latest U.S. Drought Monitor has slightly more than half the state in at least the “abnormally dry” category and 11 percent in “moderate drought”. Most of the impacts so far have been in agriculture and horticulture and not water supplies.
There is a strong La Niña occurring in the Pacific. Based on past events, Illinois is typically warmer and drier than normal during fall (September-November). By winter (December-February), the wetter than normal conditions typically appear in Illinois.

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.