The latest NWS forecast has a frost advisory for northwest Illinois and an extensive area with freeze warnings that cover KS, NE, SD, MN, IA, and WI.
A frost advisory is issued when the minimum temperature is forecasted to be 33 to 36 degrees on clear, calm nights during the growing season. They are issued in the fall until the end of the growing season (marked by the occurrence of that first widespread freeze). Tender plants can be damaged by frost and should be covered or moved indoors.
Air temperature is measured at a height of 5 feet. Colder, denser air near the ground can drop below freezing even when the measured air temperature at 5 feet is 33 to 36 degrees.
A freeze warning is issued when significant, widespread freezing temperatures are expected. They are issued in the fall until the end of the growing season (marked by the occurrence of that first widespread freeze). Continue reading “Jack Frost Getting Closer to Illinois”
Warm Start to October in Illinois, Midwest
Illinois and the Midwest are off to a warm start in October, as this temperature departure map shows. Temperatures across southern Illinois, as well as southern and western portions of the Midwest are running 4 to 6 degrees above normal. Meanwhile, central and northern Illinois, as well as the rest of the Midwest, are running 6 to 10 degrees above normal.
So far, October precipitation has been light across the southern half of Illinois and for much of the southern Corn Belt. A band of 1 to 3 inches of rain extends from KS/OK through MO, IL, IN, and up into Michigan and another band extends up into NE, IA, MN, and the eastern Dakotas. Meanwhile, eastern IA and much of WI saw little precipitation.
Trends in September, October in Illinois
Changes in the climate of Illinois can sometimes be seen in the monthly temperature and precipitation and sometimes not. Unlike the other three seasons, fall in Illinois tends to be non-trendy (like my wardrobe). Here are the time series of temperatures and precipitation for September and October for Illinois.
All four plots show a considerable amount of year to year variability. Some decades were more volatile than others. Some of the biggest swings in temperatures in September occurred in the 1920s and 1930s. On the other hand, if you take out the three really wet Octobers of 1919, 1941, and 2009, the October precipitation is fairly consistent from one year to the next and usually within 2 inches of the 1981-2010 normal.
There are no significant trends in temperature over the last century. September precipitation has a small downward trend of 0.5 inches over the last century while October precipitation shows a slight upward trend of 0.6 inches over the last century. As a result, they largely cancel each other out.
We will cover November trends in a separate post, but it’s fair to say that November is much more interesting. The horizontal line in each graph is the 1981-2010 average (aka normal).
Continue reading “Trends in September, October in Illinois”
Sixth Warmest September in Illinois
Temperature
[Update 10/6/2016] New numbers released by NCEI indicate that September was the 5th warmest on record for Illinois, instead of the 6th warmest. The statewide average temperature was 70.9 degrees, 4.7 degrees above normal. That was 0.2 degrees warmer than the preliminary number I provided at the end of the month. It is tied in 5th place with 1998. The warmest September on record was a tie between 1933 and 1925 with a statewide average temperature of 72.2 degrees.
The average statewide temperature for January through September of this year was 57.8 degrees, 2.1 degrees above normal and the 5th warmest January through September on record. Here is the month by month breakdown of statewide temperature departures for 2016. Every month, except May, has been warmer than the 1981-2010 normal.